Tesi di laurea presso il Consorzio RFX

Il Consorzio RFX propone a studenti di corsi di laurea triennale e magistrale in Fisica e Ingegneria, tesi di laurea su diversi argomenti di studio, nell’ambito della ricerca sulla fusione.
Le tesi si svolgono presso i nostri laboratori sotto la supervisione di ricercatori del Consorzio e docenti dell’Università di Padova.
La tesi può essere sperimentale, teorica, numerica o compilativa.

Fisica

Tesi Triennali
proposte dal Consorzio RFX

Categorizzazione di “segnali calcio” nelle piante in risposta a stimoli esterni.

Proponente/Relatore RFX: A. Rigoni-Garola, V. Antoni

Relatore accademico: G. Serianni

Capogruppo RFX: C. Taliercio

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Lo ione calcio svolge un ruolo di segnalazione chiave nelle piante ed è coinvolto in un’ampia gamma di processi fisiologici quali la crescita, lo sviluppo e la risposta allo stress. Studi recenti hanno dimostrato che il trattamento con acqua attivata dal plasma (PAW) può portare ad un aumento dei livelli di calcio intracellulare nelle piante, che a sua volta attiva varie vie di segnalazione coinvolte nella crescita delle piante e nella tolleranza allo stress. Obiettivo della tesi è organizzare in un unico database i segnali calcio espressi da individui diversi della stessa specie botanica esposti a diverse PAW.  In particolare le diverse PAW corrisponderanno all’esposizione a  due diverse sorgenti di plasma ( torcia e scarica a barriera dielettrica) e per diversi  tempi di attivazione. Il database così ottenuto verrà successivamente analizzato  mediante un algoritmo di tipo machine learning così da poter rilevare le caratteristiche medie dei segnali calcio  che emergono dalla risposta dei singoli individui. L’intero lavoro di tesi sarà svolto in ambiente python e jupyter, mentre gli strumenti utilizzati saranno Pandas per la creazione del database di dati e TensorFlow o Pytorch per la definizione del modello di ML.

Competenze necessarie per svolgere con successo la tesi: Sono consigliate la conoscenza del linguaggio di programmazione python e una certa dimestichezza con l’ambiente GNU-linux

Data della proposta: 31/03/2023

Design of a cut-off probe for SPIDER

Proponente/Relatore RFX: Carlo Poggi

Relatore accademico: M. Zuin

Capogruppo RFX: M. Zuin

Responsabile di Programma RFX:

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

SPIDER is the prototype of ITER heating neutral beams. It aims to produce up to 50A of negative hydrogen ions, divided in 1280 beamlets, and accelerate them up to 100keV. During its first years of operation, SPIDER plasma properties were characterized using spectroscopic measurements or electrostatic probes. However, none of these methods was able to directly measure the electron density. For this reason, the design of a cut-off probe is ongoing. This probe is made of two antennas, one acting as transmitter and one as receiver, with the transmitter sending signals over a wide range of frequencies. If a plasma is present between the two antennas, the signal measured by the receiver gets damped at the plasma frequency, which depends on the plasma density according to the relation

By measuring this damping frequency, it is therefore possible to directly measure the plasma density.
The aim of this thesis is the design of a cut-off probe for the use in SPIDER, using CST software for the electromagnetic simulations and testing the prototype probe in a small RF ion source.

Competenze necessarie per svolgere con successo la tesi: Fisica 2, Fondamenti di fisica dei plasmi

Data della proposta: 31/03/2023

Caratterizzazione del fenomeno dell’ebollizione sottoraffreddata mediante accelerometri FBG

Proponente/Relatore RFX: Carlo Poggi

Relatore accademico: E. Sartori

Capogruppo RFX: M. Zuin

Responsabile di Programma RFX:

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Il fenomeno dell’ebollizione sottoraffreddata (nucleate boiling) avviene quando la temperatura della superficie di un canale di raffreddamento è superiore alla temperatura di saturazione del fluido, portando alla formazione di piccole bolle alla parete e migliorando le proprietà di scambio termico tra la parete e il fluido. Queste bolle tendono a muoversi verso il centro del canale, dove incontrano una regione a temperatura minore e quindi a implodere (cavitazione), con conseguenze anche distruttive sulle strutture del canale.

Lo scopo della tesi è di caratterizzare lo spettro di frequenza tipico dell’ebollizione sottoraffreddata su un setup che simula i condotti di raffreddamento di un esperimento da fusione, utilizzando un accelerometro basato sul principio del Fiber Bragg Grating. Lo studente contribuirà alla messa in funzione dell’apparato sperimentale, alla raccolta dei dati sperimentali e alla loro analisi interpretativa.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Plasma velocity during magnetic reconnection

Proponente/Relatore RFX: M. Veranda

Relatore accademico: T. Bolzonella

Capogruppo RFX: S. Cappello

Responsabile di Programma RFX: L. Marrelli

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Magnetic reconnection is a ubiquitous phenomenon in nature, both in space and in laboratory hot plasmas, where it occurs continuously. It is the change of topology in magnetic field lines confining hot plasmas and, in experiments for the production of energy using nuclear fusion, it is associated with the presence of instabilities of the confining magnetic field, and with a rapid release of the plasma’s magnetic energy, which converts into the kinetic energy of its constituent particles.

This thesis deals with the main models to describe reconnection: the student learns the theory of reconnection using the magnetohydrodynamic model, and then focuses on the behavior of the velocity field. He will analyze the results of the model used to describe plasmas, and will deal with graphic visualization of the velocity field: this will help understanding better the dynamics of magnetic reconnection. The work will take place at the theory and advanced simulation group at Consorzio RFX.

Competenze necessarie per svolgere con successo la tesi: Basic knowledge of plasma physics

Data della proposta: 31/03/2022

Tesi Magistrali
proposte dal Consorzio RFX

A deep-learning approach for the analysis of calcium signal in the characterization of the biological response of plants to external stimuli

Proponente/Relatore RFX: A. Rigoni-Garola, V. Antoni

Relatore accademico: G. Serianni

Capogruppo RFX: C. Taliercio

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The calcium ion plays a key signaling role in plants and is involved in a wide range of physiological processes such as growth, development and response to stress. Recent studies have shown that plasma activated water (PAW) treatment can lead to increased intracellular calcium levels in plants, which in turn activates various signaling pathways involved in plant growth and stress tolerance. The aim of the thesis is to organize in a single database the calcium signals expressed by different individuals of the same botanical species exposed to different PAWs. In particular, the different PAWs will correspond to exposure to two different plasma sources (torch and dielectric barrier discharge) and for different activation times. The database thus obtained will be subsequently analyzed using a machine learning algorithm so as to be able to detect the average characteristics of the calcium signals that emerge from the response of single individuals.

The work plans to identify and evaluate various models suitable for signal analysis and classification; a non-supervised approach is proposed. Starting from the experimental data, a database will then be built, suitably recorded so that the signals are compatible with the input to the models and subsequently the database will be analyzed to extract the main characteristics by comparing them with the known characteristics. The entire thesis work will be carried out in a python and jupyter environment, while the tools used will be Pandas for the creation of the data database and TensorFlow or Pytorch for the definition of the ML model

Competenze necessarie per svolgere con successo la tesi: Knowledge of the python programming language and a certain familiarity with the GNU-linux environment are recommended

Data della proposta: 31/03/2023

Simulation of plasma parameters towards the optimization of first wall components by Glow-Discharge Cleaning

Proponente/Relatore RFX: S. Ciufo, R. Milazzo

Relatore accademico: M. Zuin

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: L. Marrelli

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The Glow-Discharge Cleaning (GDC) is one of the most important technique for wall conditioning in fusion experiments. It is usually employed by considering only the current required for sputtering on the first wall materials and with relatively high voltages. The purpose of this thesis is to adapt a Particle-In-Cell (PIC) code in order to simulate plasma-wall interactions from the perspective of the RFX facing Carbon tiles. In particular, energy distribution and impact angles are quantities that must be estimated, depending on boundary conditions, so to serve as input for modeling solid-state phenomena (sputtering, impurity retention/desorption, defect generation, etc.) that determine fusion performance in turn. The importance of this study lies in gaining understating of the physics ruling plasma-wall interactions and the correct application of boundary condition. In this way, GDC operations can be significantly optimized by reduction in the resources required for the operation and in the time required for execution. The candidate’s thesis will focus on adapting the PIC code to create a map enclosing energy and angles for different species contained in the plasma and with respect to the facing wall. Results will be analysed to describe plasmas and they will deal with graphic visualization of the abovementioned parameter space with final aim of better understanding the dynamics of plasma-wall interaction. The work will take place at Consorzio RFX.

Competenze necessarie per svolgere con successo la tesi: Basic knowledge of Plasma and Solid State Physics, basics of coding and analysing software

Data della proposta: 31/03/2023

Rotational and Vibrational Temperatures of H2 molecules in SPIDER negative ion source

Proponente/Relatore RFX: B. Zaniol, I. Mario

Relatore accademico: M. Agostini

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Spider is the prototype of negative ion source for ITER neutral beams, in development at Consorzio RFX, Padova. To help optimising the negative ion production, Spider is equipped with a full set of optical diagnostics that analyse the EM radiation spontaneously emitted by the plasma inside the source. Due to its large dimension, about 2 m x 1 m x 0.5 m, the measurements are carried out along more than 100 lines of sight, so to cover the entire plasma source. Part of the optical diagnostics are spectroscopy based and they produced wavelength resolved spectra in VUV-VIS range. From the analysis of Fulcher band emission between 600 nm and 640 nm, the rotational and vibrational temperatures of gas molecules can be obtained. Aim of the thesis is to derive these temperatures in the collected spectra and to study their dependence on the different experimental conditions of SPIDER source.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Spectroscopic characterisation of SPIDER negative ion source in UV-VIS range

Proponente/Relatore RFX: B. Zaniol, I. Mario

Relatore accademico: M. Agostini

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Spider is the prototype of negative ion source for ITER neutral beams, in development at Consorzio RFX, Padova. To help optimising the negative ion production, Spider is equipped with a full set of optical diagnostics that analyse the EM radiation spontaneously emitted by the plasma inside the source. Due to its large dimension, about 2 m x 1 m x 0.5 m, the measurements are carried out along more than 100 lines of sight, so to cover the entire plasma source. Part of the optical diagnostics are spectroscopy based and they produced wavelength resolved spectra in the range between 300 nm to 900 nm. By analysing these spectra, it possible to monitor the impurities content of the plasma, and with the help of emission models to gather information on the electron density and temperature. Aim of the thesis is to characterise SPIDER optical emission against the variation of the experimental condition, with particular attention to spatial non uniformities.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

A Thomson scattering diagnostic for measurements of Te and ne in the DTT divertor

Proponente/Relatore RFX: L. Giudicotti

Relatore accademico: L. Giudicotti

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Thomson scattering (TS) of laser light is a well known diagnostic technique for the measurement of electron temperature Te and electron density ne in fusion plasmas. For the new italian experiment DTT a TS system is under development for measurements in the divertor region. In this system, a laser pulse with time duration of ~10 ns ns is sent into the plasma and is observed side-on. The electron temperature Te and density ne are determined by the spectrum of the scattered radiation. The plasma conditions in the divertor region pose considerable challenges for the design of the experiment and require a careful optimization of the characteristics of the experimental apparatus. In the framework of this activity the student will first achieve a general knowledge in TS diagnostics, by developing advanced modelling techniques of the scattering process from the plasma in the DTT divertor. Then he/she will carry out the selection pf the detectors and  the optimization of the polychromators for the spectral analysis, through an estimate of the signals expected and their measurement errors.

Competenze necessarie per svolgere con successo la tesi: ‪Good aptitude to experimental work. Basic programming. Knowledge of laser and optics physics are welcome but not mandatory

Data della proposta: 31/03/2023

Diagnostic of DTT fusion plasmas by Thomson scattering of laser light

Proponente/Relatore RFX: L. Giudicotti

Relatore accademico: L. Giudicotti

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract

Thomson scattering (TS) of laser light is a well known diagnostic technique for the measurement of spatial profiles of electron temperature Te and electron density ne in fusion plasmas. For the new italian experiment DTT a TS system based on the LIDAR approach is being considered. In LIDAR TS, a laser pulse with time duration of ~150 ps (corresponding to a spatial extension of ~4.5 cm) is sent into the plasma and observed from the back. The spatial profile of Te and ne is determined measuring the time evolution of the backscattering light. This technique poses considerable experimental challenges and requires the most advanced solutions in terms of laser and optics technology. In the framework of this activity the student will first achieve a general knowledge in TS diagnostics, by developing advanced modelling techniques of LIDAR TS process and working on the integration of state-of-the art lasers, detectors and high speed digitizers in the diagnostic. In addition she/he will be involved in laboratory tests for the complete characterization of critical TS components such as very high speed MCP-PMT detectors, very high speed digitizers and filter polychromators.

Competenze necessarie per svolgere con successo la tesi:

‪Good aptitude to experimental work. Basic programming. Knowledge of laser and optics physics are welcome but not mandatory.

Data della proposta: 31/03/2023

Setting up of a spectroscopic measure on Minion negative ion source

Proponente/Relatore RFX: I. Mario, B. Zaniol

Relatore accademico: G. Serianni

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

To studying the coupling between an RF oscillator and a plasma source for negative ion production, a new test bed, Minion, is under construction at Consorzio RFX, Padova. Minion will be equipped with a full set of optical diagnostics that analyse the EM radiation spontaneously emitted by the plasma inside the source. One of the optical diagnostics has to provide wavelength resolved spectra in VUV-VIS range. While the spectrometer and the detector were already identified, the optical interfaces and other details, as the grating grooving, are still to be finalised. Aim of the thesis is to complete the diagnostic design, and then to proceed with its assembly, its testing and calibration, and finally its coupling with Minion.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Density limit in the RFXmod tokamak

Proponente/Relatore RFX: P. Zanca, F. Auriemma

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: L. Marrelli

Tipologia: SperimentaleTeorica, Numerica, Compilativa

Abstract:

In magnetic confinement fusion devices, it is important to operate at high plasma density, since the fusion reaction rate scales with the square of this quantity. However, a general feature of magnetic confinement devices is the existence of a limit in the possibility of raising the plasma density (density limit). Many mechanisms have been proposed to explain this phenomenon, but no consensus has been obtained so far. We propose to investigate the density operative space of RFXmod in the tokamak configuration. In particular, the dependence of the maximum attained densities on the main plasma parameters will be investigated, with the aim of characterizing an empirical scaling law for the density limit in the RFXmod tokamak. Then, a comparison with present different models of the density limit will be carried out.

Competenze necessarie per svolgere con successo la tesi: Fundamental notions of plasma physics

Data della proposta: 31/03/2023

PL Threshold studies in the JET tokamak

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Motivation: Radiation control in D, T, and DT baseline plasmas is being reviewed [L. Piron 2022 SOFT papers submitted]. The discharges last longer when the optimal gas-fueling recipe combined with the use of pellet injection (ELM control) have been used. However, the discharges in T and DT suffer from radiation issue in a faster time scale w.r.t. to D ones. Why?

Strategy:

Investigate PLH transition metrics in D,T,DT plasmas performed in 2021

Compare the results with real-time metrics

Design experiments for DTE3 campaign

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Stability analysis of SMART equilibria using MARS-F

Proponente/Relatore RFX: L. Piron, E. Viezzer (University of Sevilla)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The main goal of the SMART tokamak is to explore the prospects of Negative Triangularity shaped plasmas for a future fusion power plant (FPP) based on spherical tokamaks. Although NT plasmas offer some attractive features for a future FPP, they are also typically more prone to magnetohydrodynamic (MHD) fluctuations. In this work, the MHD code MARSF will be used to explore the stability of SMART plasmas with positive vs negative triangularity. This Thesis project can be performed within the ERASMUS+ program.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Resonant field amplification in JET high pressure scenarios

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In magnetic fusion devices to probe plasma stability, magnetic field perturbations induced by means of external coils are applied in high pressure regimes in the so-called resonant field amplification technique. Such a technique has been extensively applied in high-beta plasmas performed in the JET tokamak (Culham, Oxfordshire, UK). In this project, data from multiple diagnostics, such as magnetics, Thomson scattering, and equilibrium reconstructions will be analyzed to characterize the plasma amplification process.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Modeling and simulation of Alfvén instabilities and zonal structures in tokamak plasmas

Proponente/Relatore RFX: L. Piron, A. Biancalani (University of Paris)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Tokamak plasmas are an example of systems where the dynamics is intrinsically multiscale. Microscopic turbulence generated by the gradients of the plasma temperature coexists with meso-scale

zonal flows (nonlinearly generated by the turbulence, analogously to the latitudinal bands in Jupiter) and meso-scale / macro-scale Alfvén instabilities.

Understanding the dynamics of zonal structures is particularly important because they have a crucial role in decreasing the turbulence levels. Recently, it has been seen that zonal structures can also be excited by Alfvén instabilities. Consequently, this has been proposed as a possible new mechanism for explaining the reduction of turbulence observed in experiments (see for example [1]).

Starting date: March 2023.

Duration: 6 months.

This paid internship has a maximal length of 6 months, to start in March. The topic is developed in the framework of the Eurofusion projects TSVV10 and ATEP. In this internship, the student will study the Alfvén instabilities in experimentally relevant configurations and estimate the amplitude and spatial structure of the zonal structures nonlinearly driven by these Alfvén instabilities.

References:

[1] A. Biancalani, A. Bottino, A. Di Siena, O. Gurcan, T. Hayward-Schneider, F. Jenko, P. Lauber, A. Mishchenko, P. Morel, I. Novikau, F. Vannini, L. Villard, A. Zocco, “Gyrokinetic investigation of Alfven instabilities in the presence of turbulence”, Plasma Phys. Control. Fusion 63, 065009 (2021)

Competenze necessarie per svolgere con successo la tesi: The student who wishes to apply should be in the M2 year, and should have a good knowledge of plasma physics and programming languages (Matlab or Python).

Data della proposta: 31/03/2023

Magnetohydrodynamic stability analysis of the pedestals of ASDEX Upgrade plasmas

Proponente/Relatore RFX: C. Angioni (IPP)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The high confinement mode (H-mode) dramatically improves the confinement properties of present tokamak plasmas and is therefore the scenario envisioned for future fusion reactors. The main characteristic of this scenario is the formation of a pedestal at the edge of the plasma by means of a transport barrier. The height of the pedestal is limited by the onset of edge localized modes (ELMs), quasi-periodic explosive instabilities at the plasma edge which expel particles and energy on millisecond time-scales. While ELMs in present day machines pose no danger, when scaled to a fusion reactor device they are predicted to cause significant damage to the machine components. As such, the understanding and exploitation of alternative regimes with high confinement but without ELMs is of significant interest. The onset of an ELM can be described by magnetohydrodynamic (MHD) stability codes.

This project involves the automation of a workflow which runs codes to test the pedestal MHD stability (such as MISHKA) starting from a standardized set of experimental information. Once this workflow has been implemented it should be applied to a database of experimental data from the ASDEX Upgrade tokamak to study the properties of the pedestal in ELMing and different ELM-free regimes. It is particularly important to provide an estimate of the distance to the MHD stability boundary in the various ELM free regimes to understand how robust these regimes are and the margin a given regime has before a large ELM is triggered.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Integrated core scrape-off layer modelling of JET deuterium-tritium baseline plasmas

Proponente/Relatore RFX: L. Garzotti (UKAEA)

Relatore accademico: . Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

JET performed a deuterium-tritium (DT) campaign in 2021 producing record fusion power and a wealth of experimental data for analysis and interpretation. One of the most important aspects to be investigated is the combined dynamics of the core and the scrape-off layer of the plasmas produced in DT, which is responsible for their confinement properties, the interaction with the first wall, the fueling requirement and, ultimately the performance in terms of fusion power. The proposal for this thesis work is to model a limited set of JET DT plasmas with state-of-the art integrated modelling codes to investigate the physics of the phenomena above mentioned. Initially the work will be limited to one of the aspects of the plasma phenomenology to progressively include more of them if time allows it.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Diagnostic Data Integration Using Deep Neural Networks for Real-Time Plasma Analysis

Proponente/Relatore RFX: L. Piron, A. Rigoni Garola

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In this project, deep neural networks will be applied for diagnostic data integration in the complex scenario of the active control for magnetically confined fusion plasmas.

A database of 60000 signals acquired by the Soft-X-Ray diagnostic in the RFX-mod experiment will be analyzed to reconstruct plasma temperature profiles.

The network topology called variational auto encoder (D. P. Kingma and M. Welling, “Auto-encoding variational Bayes,” in Proc. 2nd Int. Conf. Learn. Represent. (ICLR), Banff, AB, Canada,Y. Bengio and Y. LeCun, Eds., Apr. 2014. http://arxiv.org/abs/1312.6114) will be adopted to add useful information to the reconstruction of the missing temperature points.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Development of a Wall Conditioning system for the SMART tokamak

Proponente/Relatore RFX: E. Viezzer

Relatore accademico: L. Piron

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Wall conditioning is key to improve the plasma performance in a magnetically confined fusion reactor as impurities released from the wall can cool down the plasma until its collapse. Several methods are typically used to condition the reactor wall, and, among others, in this work glow discharges and boronization will be explored as main wall conditioning methods for the SMART tokamak. The Thesis project can be performed within the ERASMUS+ program.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Characterization of magnetic field errors in MAST-U coil manufacturing

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Error fields are spurious magnetic field perturbations that can degrade the plasma performance in magnetic fusion devices through various mechanisms, such as rotation braking, fast particles losses and MHD instability onset. The identification of error field sources thus plays a vital role to guarantee safe and robust plasma operations. In this project, the validation of a 3D electro-magnetic modelling of poloidal field coils again experimental data will be carried to detect error field sources in the coil manufacturing process in the MAST-U device (Culham, Oxfordshire, UK).

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Assessment of the concept feasibility of spin-offs from magnetic fusion research

Proponente/Relatore RFX: L. Piron, P. Martin

Relatore accademico: L.Piron, P. Martin
Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Interest on magnetic fusion energy research has rapidly evolved over the years according to the need of developing new energy technologies able to fulfil the increase energy demand, while not impacting on the global climate change. The goal of harnessing the magnetic fusion energy indeed is to produce power for mankind which is virtually unlimited, intrinsically safe and completely free of any greenhouse gas emissions and radioactive waste.

Given its complex, multidisciplinary nature and tantalizing challenge posed, it should be no surprise that magnetic fusion energy research has driven numerous spin-offs, which are proposing to contribute on fusion research on the way to fusion electricity.

The aim of this project is to perform a concept feasibility study of magnetic fusion spin-offs, by reviewing the state of the art for spin-offs fusion applications.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Analysis of disruption paths in TCV via Machine Learning

Proponente/Relatore RFX: L. Piron, A. Pau (EPFL)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In the last years, data science methods from the fields of machine learning and artificial intelligence (ML/AI) have offered several opportunities for accelerating the progress towards the realization of fusion energy. The massive amount of data available from current operating tokamaks, together with the exponential growth of computing and cloud technologies, have enabled new scenarios in the framework of advanced data analysis and processing. The work proposed for this Master Thesis fits in different priority research opportunities in Fusion, where “Data-enhanced Physics Informed Prediction” is one of the emerging topics and deals with, among the other things, plasma state monitoring, exception handling, off-normal events, and disruptions.

Disruptions are a catastrophic loss of plasma thermal and magnetic energy potentially causing severe damage to the machine and they represent one of the main concerns for the exploitation of the tokamak concept in future fusion power plants. The proposed work will focus on the development of a hybrid framework (data-driven and physics-based) for predicting and reacting to the most common precursor of disruptive terminations in the TCV Tokamak, such as MHD instabilities and Vertical Displacement Events (VDE). The prediction of such events, combined with model-based approaches, can improve the response of the Plasma Control System, and help in designing and optimizing plasma termination schemes. The proposed activities have also a direct connection with the Task of the ITPA MHD, Disruptions and Control Topical Group dealing with the design of the trigger generation function and control logic for the ITER Disruption Mitigation System, and with the EUROfusion Work Package for Tokamak Exploitation (experiments on this specific topic are planned for 2023).

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Advanced locked mode detection in the TCV tokamak

Proponente/Relatore RFX: L. Piron, A. Pau (EPFL)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In the last years, the exponential growth of computing and cloud technologies, have enabled new scenarios in the framework of advanced data analysis and processing. A large amount of high-dimensional data is produced daily by many diagnostics systems measuring various plasma properties during the experiments. One of the most important systems in a Tokamak is the set of magnetic sensors used to monitor Magnetohydrodynamic (MHD) activity and detect onset and development of MHD instabilities potentially causing a disruption. Disruptions are a catastrophic loss of plasma thermal and magnetic energy potentially causing severe damage to the machine, and they represent a key research priority in the fusion roadmap. MHD instabilities are often seen as precursors to disruptions. The detection of these modes can be used to predict disruptions and is routinely used in different machines (such as in the JET tokamak) to trigger the disruption mitigation system.

MHD modes, often rotating, can stop rotating (mode locking) with respect to the plasma frame, leading eventually to disruption. The slowing down of the mode rotation velocity as well as the amplitude of the locked mode can be detected respectively by measuring the oscillating field perturbation in tangential field pick up coils or Mirnov coils, and the effective amplitude of the radial component of the mode based on saddle coils measurements.

The presence of vacuum field pickup, misalignment between sensors and axisymmetric coils, DC & AC coupling between coils and sensors can pollute the measured plasma 3D field, making MHD mode detection challenging. One of the objective of this thesis is to develop and implement real-time algorithms to remove unwanted component through AC and DC compensations (such as in https://aip.scitation.org/doi/pdf/10.1063/5.0101630) and derive a robust locked mode detector for the TCV Tokamak. An additional objective would be to compare the locked mode amplitude to trigger a disruption in TCV with the scaling proposed in https://iopscience.iop.org/article/10.1088/0029-5515/56/2/026007#references.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Laser-aided diagnostics on a negative ion source for fusion

Tutor RFX: R. Agnello, M. Barbisan

Academic supervisor: G. Serianni

Group leader: L. Carraro

Responsabile di Programma: Vanni Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Topic of thesis: negative ion sources, laser-plasma diagnostics

Abstract:

Laser-based diagnostics for plasmas are essential tools to characterize negative ion sources for fusion. In SPIDER, the full-scale source prototype for ITER, two techniques are routinely employed: the Cavity Ring-Down Spectroscopy (CRDS) and the Laser Absorption Spectroscopy (LAS).  CRDS is based on a high finesse optical trap in which a laser beam, travelling back and forth, photo-ionizes the negative ions (H-, D-) providing a measure of their line-integrated volumetric density. LAS measures the volumetric density of caesium atoms evaporated inside the source, one of the main ingredient required to optimize negative ion production. Both techniques require accurate calibration and constant monitoring due to their sensitivity and, especially, during the experimental campaigns, they are crucial to promptly provide the source operators with useful feedbacks to properly run the facility.

The careful monitoring of these techniques is therefore essential to guarantee a constant and reliable inflow of data to drive the experimental campaigns.

The thesis project is structured as follows:

  • Preliminary study/training
  • Literature research. Study of laser-plasma interaction. Laser safety course. Study of the results obtained in the previous experimental campaigns.
  • Detailed numerical studies. Model for Cavity Ring-Down Spectroscopy and Cs absorption spectroscopy.
  • Experimental activities
  • Calibration and alignment of optical diagnostics. Characterization of the signals in vacuum. Participation in the experimental campaign. Support in data analysis.
  • Comparison with other diagnostics. Possible application of the collisional radiative model for caesium.

Required skills: familiarity with laboratory equipment and any programming language.

Proposal date:  May 2023

Development of a mm-wave interferometric system for a negative ion source for fusion

Tutor RFX: R. Agnello

Academic supervisor: G. Serianni

Groupleader: R. Pasqualotto

Responsabile di Programma: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Topic of thesis: mm-wave interferometry, negative ion sources

Abstract:

Heating Neutral Beam (HNBs) injectors for fusion are complex and large devices featuring a plasma source for the production of negative ions, a multi-grid electrostatic accelerator and a gas neutralization system. At the Neutral Beam Test Facility (NBTF) located at Consorzio RFX, in Padova, research and development for the full-scale HNBs (SPIDER and MITICA experiments) for ITER has recently achieved significant milestones. In SPIDER, stable plasmas discharges are obtained by eight radiofrequency sources, called drivers, powered by RF generators. However, the overall properties of the resulting plasma depends not only by the single RF drivers but also on other factors such as the mutual electromagnetic interactions between the drivers, the presence of a magnetic field used to mitigate undesired electrons and the dynamic of the evaporated caesium used to increase source ion extraction performances.

To understand the multifaceted physics of these experiments, compact devices are also operated to investigate single phenomena.

Recently, to enhance the performance of a single driver in terms of plasma density and negative ion production, a novel negative radiofrequency named “Driver Plasma Experiment” (DPE) is currently under development in parallel to the leading experiments. The purpose of this small-scale device is twofold: verifying the effectiveness of a new electromagnetic configuration to improve SPIDER plasma confinement, and, in the long term, setting up a single-driver experimental facility equipped with a full suite of diagnostics.

Among the usual diagnostics such as electrostatic probes and emission spectroscopy, a mm-wave interferometer, envisaged for DPE, offers the advantage of being non perturbative, directly measuring the plasma density and exhibiting an excellent time-resolution accuracy. The implementation of this technique, however, requires dedicated numerical investigations, the experimental characterization of microwave components and wave field measurements.

The thesis project is structured as follows:

  • Preliminary studies/activities on
  • Theory of propagation of mm-wave beam. Quasi-optical propagation. Gaussian beams. Guided propagation of electromagnetic waves. Inductively coupled plasma generation. Negative ion production by volume and surface processes.
  • Propagation of wave in plasmas. Interferometry and reflectometry techniques.
  • Interferometry in basic plasma devices and fusion machines. Bibliography research on other fusion experiments (RFX and TCV).
  • Development of a conceptual design for DPE interferometer. Waveguide path and injection side. Compatibility with other diagnostics.
  • Modeling activities
  • Training in COMSOL and CST.
  • Modelling of mm-wave propagation in waveguides and source enviroment. Study of possible mode conversion. Study of antenna radiating pattern. Attenuation along the waveguide paths. Estimate of signal-to-noise ratio.
  • Study of possible focusing elements such as microwave lenses. Optimized horn antenna.
  • Experimental activities
  • Measurement of the radiative pattern with a radiometer. Test with different antennae. Comparison with numerical models.
  • Participation in the assembly of the experimental setup. Characterization of cavity modes. Performance test with a dielectric material.

Participation in the experimental campaign. Measurement in the plasma. Effect of parametric scans: magnetic filter field, RF power, scattering of waves by a displacing plasma. Comparison with numerical models and other plasma diagnostics.

Required skills: familiarity with laboratory equipment and any programming language.

Proposal date:  May 2023

Turbulence simulation of the plasma boundary of RFX-mod operating as tokamak and comparison to experimental data

RFX Supervisor: N. Vianello

Academic supervisor: M. Giacomin

Head of the RFX research group: M. Zuin

Leader of the RFX research program: T. Bolzonella

Tipologia: Modelling, Teorica, Numerica, Compilativa

Abstract:

RFX-mod is a toroidal device with minor radius a = 0.46 m and major radius0 = 2 m located at Consorzio RFX, Padua, which confines plasmas by means of magnetic fields.  Thanks to its flexibility, RFX-mod can operate as both reversed field pinch and tokamak. Experiments in RFX-mod convers a wide area of plasma physics, from basic plasma physics experiments to fusion applications. The external plasma region of tokamak, denoted as scrape-off layer (SOL), is characterized by intermittent and filamentary turbulent structures that propagate radially. A recent experimental work has detected and tracked turbulent filaments in the SOL of RFX-mod operating as tokamak from data measured with a 2D array of Langmuir probes (G. Grenfell et al, Nuclear Fusion 60 (2020) 126006). By leveraging these experimental results, the aim of this thesis project is to numerically investigate filamentary turbulence in the SOL of RFX-mod by using the GBS code (M. Giacomin et al, Journal of Computational Physics 463 (2022) 111294). GBS is a three-dimensional turbulent code that evolves two-fluid equations in the boundary region of magnetic fusion devices in arbitrary magnetic configuration. The thesis project is structured in three main parts. The first part consists in running GBS simulations in simplified geometry and in getting familiar with various numerical tools used to analyze plasma turbulence in the SOL. RFX-mod tokamak turbulence simulations will be performed and analyzed in the second part, which also involves some analytical work. The last part is dedicated to the comparison against existing experimental data. If time allows, the numerical analysis will be used to inform the design of future plasma boundary turbulence diagnostics to be used in the upcoming upgrade of RFX-mod.

Required skills: Basic knowledge of Matlab or Python

Proposal date: 26/08/2023

Particle transport characterization in helical RFX-mod2 plasmas

Proponente/Relatore RFX: M. Gobbin
Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: L. Marrelli

Tipologia: Modelling, Teorica, Numerica, Compilativa

Abstract:

The reversed field pinch experiment RFX-mod2 will be characterized by a modified
geometry and magnetic boundary with respect to the previous version (RFX-mod), in
operation up to 2015. The activity proposed in this thesis is to investigate by a numerical
approach the particle diffusion properties in the helical plasmas of RFX-mod2 with
appropriate assumptions on the expected magnetic topology and on the temperature
profiles. To this end, both experimental data analysis and numerical modeling will be part
of the planned work. In particular, the data collected in RFX-mod by several diagnostics
like magnetic probes, interferometer, soft-x-ray and Thomson Scattering are going to
provide the inputs for the Hamiltonian guiding center ORBIT which integrates the motion
of test particles (ions and electrons) in the magnetic configuration defined for the analysis
and allows to compute the relative diffusion coefficients. Such a study, from one side,
allows predicting transport and confinement properties in RFX-mod2, from the other side,
it is useful to set up part of the analysis/numerical tools required when the upgraded device
will start operation.

Proposal date:  04/09/2023

Reconstruction of the reversed field pinch magnetic perturbations in toroidal geometry by means of Deep Learning for real-time plasma control

RFX Supervisor: A. Rigoni/R. Cavazzana

Academic supervisor: A. Rigoni

Head of the RFX research group: C. Taliercio

Leader of the RFX research program: L. Marrelli

Tipologia: Modelling, Teorica, Numerica, Compilativa

Abstract:

In view of the forthcoming operation of RFX-mod2 in reversed field pinch configuration, a significant enhancement for the experiment’s real-time control system is transitioning from the conventional simplified cylindrical approximation to the correct toroidal reconstruction. Presently the toroidal reconstruction starting from the experimental measurements, requires lengthy calculations that are impractical in real-time. Given that the solution space is reasonably well-behaved, the solving algorithm can be substituted with a Deep Learning (DL) network that can be integrated into the real-time system. The thesis consists in finding a suitable DL method to be trained using the relevant measurements, extracted from the RFX-mod database and processed using the existing toroidal reconstruction code.

The developed network will be then adapted and optimized for a real-time environment built in FPGA components.

Previous experience: background in data analysis and machine learning, python and a DL related library tools (e.g. SciKit Learn, TensorFlow, Pytorch), familiarity with Linux environment.

Proposal date: 13-09-2023

Development of a reduced turbulent transport model for the tokamak core from a database of linear gyrokinetic simulations

RFX Supervisor: M. Giacomin

Academic supervisor: M. Giacomin

Head of the RFX research group: M. Zuin

Leader of the RFX research program: T. Bolzonella

Tipologia: Modelling, Teorica, Numerica, Compilativa

Abstract:

The design of future high-performance magnetic confinement fusion devices requires accurate predictions of the energy confinement time, which is the time taken by the stored energy to leave the confined plasma. This important quantity depends on turbulent transport, whose prediction often required complex and computationally expensive first-principles nonlinear gyrokinetic simulations, becoming prohibitively expensive when multiple scenarios need to be considered.

For this reason, reduced transport models, which include a simplified physics model and are therefore significantly faster than nonlinear gyrokinetic simulations, are commonly applied in scenario development. There is a hierarchy of reduced transport models depending on fidelity level: higher fidelity models are more accurate, but also more computationally expensive, than lower fidelity models. A recent reduced transport model has been derived to specifically address turbulent transport in highly shaped electromagnetic regimes in presence of equilibrium flow shear. The core of this model is described by a quasi-linear metric that is evaluated from first-principles linear gyrokinetic simulations (much cheaper than nonlinear simulations).

The thesis project aims to exploit and improve this newly derived reduced transport model by employing machine learning techniques in order to provide a faster way to compute the quasi-linear metric than performing linear gyrokinetic simulations. In fact, although the evaluation of the quasi-linear metric is at least two orders of magnitude faster than performing nonlinear gyrokinetic simulations, it still requires hundreds of core-hours, which limits its applicability in scenario development.

The project is divided in two main parts. In the first part, the validity of the reduced transport model will be investigated in various electrostatic and electromagnetic regimes by comparing quasi-linear to nonlinear turbulent flux predictions. The reduced transport model will then be validated against a few experimental scenarios by performing simulations where the pressure profile is evolved based on the quasi-linear turbulent transport: the measured and predicted pressure profiles will be compared. This validation includes tokamak scenarios from RFX-mod, which is the magnetic fusion device at Consorzio RFX in Padua. In the second part of the project, the reduced transport model will be further simplified. A large database of linear gyrokinetic simulations covering a multidimensional space of approximately ten features will be used to train a machine learning model, which will replace the need of linear gyrokinetic simulations to evaluate the quasi-linear metric. The predictions made from the modified reduced transport model will then be compared to experimental data.

Linear and nonlinear gyrokinetic simulations will be performed with the GS2 code (https://gyrokinetics.gitlab.io/gs2/page/index.html), while the profile evolution will be carried out by using the T3D python code (https://bitbucket.org/gyrokinetics/t3d/src/main/), where the reduced transport model is already implemented.

Previous experience: Basic knowledge of Python and machine learning
Date:
14/11/2023

Ricostruzioni dei profili radiali di temperatura elettronica in RFX-mod (nei regimi a confinamento migliorato) dalle misure di Thomson Scattering e SXR

Proponente/Relatore RFX: P. Franz

Relatore accademico: L. Giudicotti

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: L. Marrelli

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The temperature profiles of electrons in quasi-single helical (QSH) states in RFX-Mod present clear transport barriers. The study of these profiles is mainly conducted using Thomson scattering, which has a time resolution limited by laser pulse repetition frequency (100 Hz). A two-foil SXR spectrometer allowed this study to be extended. Temperature profiles can be measured up to a frequency of a few kHz, and the entire temporal evolution of the electron temperature during a QSH cycle can be determined. A mapping technique, originally developed for Thomson temperature profiles, has also been applied to profiles measured with SXR diagnostics. In particular, the temperature gradients linked to the presence of transport barriers are reconstructed and analyzed in a helical reference system, consistently with the equilibrium of the underlying plasma. A clear difference in the behavior of the temperature gradient is observed between the ascending phase of the QSH and the saturated (or flattop) phase.

The proposed thesis subject is the statistical application of the method to the available QSH database. More specifically, analysis of the greatest number of Te profiles during the QSH phases, choosing the cases in which both types of profiles are available (from the TS and the SXR), will be performed. The target is the establishment and characterization of three types of electron temperature profiles: MH (without transport barriers), DAx (transport barrier with two magnetic axes) and SHAx (transport barrier with a single magnetic axis). Moreover, the study will allow to “calibrate” the Te profile from the SXR to the TS profile, which is much more resolved in space. The work will then extend the Te from SXR data analysis to follow the temporal evolution of Te profiles and gradients with a resolution of a few kHz.

The adaptation/ development/optimization of the already available software tools, will be an important element of the proposed work.

Competenze necessarie per svolgere con successo la tesi:

Good aptitude to data analysis work. Knowledge of computer language programming (Python, IDL) required.

Date: 30/11/2023

Analysis of locked dynamics in MAST-Upgrade / AUG

Proponente/Relatore RFX: Lidia Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Locked modes are MHD instabilities which can be present in magnetic fusion devices and are responsible of rotation braking, particle and energy confinement degradation, and can lead to plasma disruptions. Because of these deleterious effects, the dynamics of locked mode (triggering and its evolution) needs to be deeply investigated.

In this Thesis work, experiments performed in Work Package Tokamak Exploitation (WPTE) devices, which suffer from the presence of locked modes, will be analyzed utilizing data from multiple plasma diagnostics.

Competenze necessarie per svolgere con successo la tesi:

Date: 30/11/2023

Caratterizzazione numerica (e sperimentale) dei forni del cesio per SPIDER

Proponente/Relatore RFX: Sartori (Fadone)

Relatore Accademico: G. Serianni

Capogruppo: A. Rizzolo

Responsabile di Programma: D. Marcuzzi

Tipologia: Sperimentale, Teorica, Modellistica, Compilativa

Abstract:

Gli iniettori di neutri sono riscaldamenti ausiliari fondamentali per le macchine da fusione nucleare: la formazione del fascio di ioni negativi, precursore del fascio di neutri, avviene estraendo ioni negativi da un plasma di idrogeno. Poiché in una scarica di idrogeno la densità di ioni negativi è molto bassa, va massimizzata grazie alla evaporazione di cesio, che ricoprendo le superfici metalliche affacciate al plasma, ne riduce la funzione lavoro; pertanto, atomi di idrogeno che impattano sulla superficie possono estrarre un elettrone dalla superficie e venire riemessi come ioni negativi.

Dato il ruolo fondamentale del cesio nella produzione di ioni negativi, l’uniformità del fascio risultante dipende dalla uniformità della copertura di cesio, specialmente alle superfici vicine ai fori da cui il fascio viene estratto. L’esperimento “CATS” è equipaggiato con varie diagnostiche dedicate alla caratterizzazione della quantità di cesio evaporato, della distribuzione angolare della emissione dal forno, della probabilità di deposizione (sticking) e della funzione lavoro delle superfici esposte al vapore di cesio.

Lo studio proposto consiste 1) nella misura tramite un detector mobile Langmuir-Taylor della distribuzione spaziale del cesio emesso, e 2) della quantità evaporata al variare della temperatura del forno; 3) nella stima dello sticking del cesio alle superfici della camera, sfruttando la microbilancia e le altre diagnostiche 4) nel confronto con modelli numerici dei risultati del nuovo ugello di evaporazione all’interno della camera da vuoto di CATS.

E’ possibile adattare il progetto di tesi a seconda del tempo a disposizione e delle preferenze dello studente, anche includendo attività sperimentale sulla sorgente SPIDER.

Competenze richieste (se necessarie):

Data della proposta: 01/12/2023

Developement of the Light Impurity Tomography diagnostic for RFX-mod2 experment

Proponente: M. Agostini, M. Ugoletti

Relatore Accademico: M. Agostini

Capogruppo: L. Carraro

Tipologia: Sperimentale, Teorica, Modellistica, Compilativa

Abstract:

The Light Impurity Tomography (LIT) is a spectroscopic diagnostic for measuring the poloidal distribution of the emissivity of low Z impurities in RFX-mod2 experiment. It will observe the emission along the poloidal angle of neutral hydrogen or of other low Z impurities that are present in the edge region.

The diagnostic consists of 7 cameras, installed in 7 different portholes around the poloidal direction, with changeable interference filters. The 7 cameras observe line-integrated signals, and the 2D map of the emissivity of the specific ion species selected by the interferential filter is obtained with a tomographic inversion.

The goal of the thesis is to optimize the position of the cameras for obtaining the best reconstruction of the emissivity. Simulation of the emissivity has to be performed, together with the synthetic data of the cameras. A tomographic algorithm will be developed to obtain the poloidal emissivity to be compared to the simulated one. By minimizing the errors between the simulation and the reconstruction, the best spatial position and orientation of the 7 cameras are determined.

Competenze richieste (se necessarie): Programmazione di base
Data della proposta: 12/01/2024

Ingegneria

Tesi Triennali
proposte dal Consorzio RFX

Design of a cut-off probe for SPIDER

Proponente/Relatore RFX: C. Poggi

Relatore accademico: M. Zuin

Capogruppo RFX: M. Zuin

Responsabile di Programma RFX:

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

SPIDER is the prototype of ITER heating neutral beams. It aims to produce up to 50A of negative hydrogen ions, divided in 1280 beamlets, and accelerate them up to 100keV. During its first years of operation, SPIDER plasma properties were characterized using spectroscopic measurements or electrostatic probes. However, none of these methods was able to directly measure the electron density. For this reason, the design of a cut-off probe is ongoing. This probe is made of two antennas, one acting as transmitter and one as receiver, with the transmitter sending signals over a wide range of frequencies. If a plasma is present between the two antennas, the signal measured by the receiver gets damped at the plasma frequency, which depends on the plasma density according to the relation

By measuring this damping frequency, it is therefore possible to directly measure the plasma density. The aim of this thesis is the design of a cut-off probe for the use in SPIDER, using CST software for the electromagnetic simulations and testing the prototype probe in a small RF ion source.

Competenze necessarie per svolgere con successo la tesi:
Fisica 2, Fondamenti di fisica dei plasmi

Data della proposta: 31/03/2023

Caratterizzazione del fenomeno dell’ebollizione sottoraffreddata mediante accelerometri FBG

Proponente/Relatore RFX: C. Poggi

Relatore accademico: E. Sartori
Capogruppo RFX: M. Zuin

Responsabile di Programma RFX:

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Il fenomeno dell’ebollizione sottoraffreddata (nucleate boiling) avviene quando la temperatura della superficie di un canale di raffreddamento è superiore alla temperatura di saturazione del fluido, portando alla formazione di piccole bolle alla parete e migliorando le proprietà di scambio termico tra la parete e il fluido. Queste bolle tendono a muoversi verso il centro del canale, dove incontrano una regione a temperatura minore e quindi a implodere (cavitazione), con conseguenze anche distruttive sulle strutture del canale.

Lo scopo della tesi è di caratterizzare lo spettro di frequenza tipico dell’ebollizione sottoraffreddata su un setup che simula i condotti di raffreddamento di un esperimento da fusione, utilizzando un accelerometro basato sul principio del Fiber Bragg Grating. Lo studente contribuirà alla messa in funzione dell’apparato sperimentale, alla raccolta dei dati sperimentali e alla loro analisi interpretativa.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Ottimizzazione della emissione angolare del forno del cesio per SPIDER

Proponente/Relatore RFX: E. Sartori (Fadone, Pouradier)

Relatore Accademico: E. Sartori
Capogruppo: A. Rizzolo

Responsabile di Programma RFX: V. Toigo, D. Marcuzzi

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Gli iniettori di neutri sono riscaldamenti ausiliari fondamentali per le macchine da fusione nucleare: la formazione del fascio di ioni negativi, precursore del fascio di neutri, avviene estraendo ioni negativi da un plasma di idrogeno. Poiché in una scarica di idrogeno la densità di ioni negativi è molto bassa, va massimizzata grazie alla evaporazione di cesio, che ricoprendo le superfici metalliche affacciate al plasma, ne riduce la funzione lavoro; pertanto, atomi di idrogeno che impattano sulla superficie possono estrarre un elettrone dalla superficie e venire riemessi come ioni negativi.

Dato il ruolo fondamentale del cesio nella produzione di ioni negativi, l’uniformità del fascio risultante dipende dalla uniformità della copertura di cesio, specialmente alle superfici vicine ai fori da cui il fascio viene estratto.

Lo studio proposto consiste 1) nello studio del sistema di evaporazione usato nelle recenti campagne sperimentali di SPIDER, e dei risultati in termini di uniformità del fascio 2) nella riprogettazione e ottimizzazione degli ugelli dei forni del cesio, per cercare di ottimizzarne la emissione.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Design of in vessel pick up coils for DTT fusion experiment

Proponente/Relatore RFX: DTT DIAG-MAG team

Relatore accademico: N. Marconato
Capogruppo RFX: M. Brombin

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract: (Max 2000 caratteri, inclusa la bibliografia se presente)

The student will work for the development of an in vessel pick up coil for magnetic measurements in DTT, optimizing its design starting from the present proposal. The sensor must be carefully studied to withstand the harsh environmental conditions inside the vacuum vessel of DTT: high temperature, non-negligible neutron radiation, EM noises and vacuum compatibility. A preliminary investigation based on numerical models has to be carried out. Some tests on proposed material will be performed. The manufacturing of a prototype will allow testing the performances of the investigated design.

Competenze necessarie per svolgere con successo la tesi: Basic concepts of electrical engineering. Electronics and FEM knowledges are welcome

Data della proposta: 31/03/2023

Tesi Magistrali
proposte dal Consorzio RFX

High-frequency modelling of the Acceleration Grid Power Supply of SPIDER experiment

RFX Supervisor: A. Ferro

Academic supervisor: P. Bettini

Tipologia: Modelling, Teorica, Numerica, Compilativa

Abstract:

SPIDER is the test-bed of the negative ion beam source of the ITER Heating Neutral Beam Injectors (NBI). The Acceleration Grid Power Supply (AGPS)provides negative dc voltages up to-96 kV to the SPIDER acceleration grids, and dc currents up to 75 A. Frequent arc breakdowns occur between the acceleration grids, due to the short gap required by the beam optics. They represent short-circuits at the AGPS output, which cause voltage collapse and high frequency voltage and current oscillations, which stress the AGPS and the other items connected at the same potential. A thesis is proposed, aiming at studying the propagation of these voltage transients along the AGPS output cable, and the voltage fluctuations occurring on the AGPS. The work includes the development of a high-frequency model of the AGPS components, considering the stray inductances and capacitances, estimated analytically, from test reports or through measurements on the field. The results of the model will be compared with the available measurements to provide a first validation, and will give useful inputs to define possible improvements of the plant.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Analysis of the performance of the Toroidal Power Supply of RFX-mod2 after the upgrade

Proponente/Relatore RFX: F. Santoro

Relatore accademico: P. Bettini

Capogruppo RFX: E. Gaio

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The Toroidal Power Supply system of RFX-mod is composed of an ac/dc thyristor converter, rated for 3 kV and 16 kA, which feeds 12 identical sectors, divided into 2 groups. Each sector has a dc capacitor bank that feeds an IGCT-based four-quadrant converter, rated for 3 kV and 6 kA. The power supply proved to be reliable and flexible, but in the past experimentation of RFX-mod it resulted the need of more stringent performance in terms of latency, precision of the controlled current and synchronism between the two power supply groups of the two sectors, which were initially not foreseen.

In view of the upgraded RFX-mod2, is under design an enhancement of the Toroidal Power Supply, which consists in a reconfiguration of the circuit that could allow overcoming the problems of synchronism between groups and improving precision of the control system.

After the modification, the Toroidal Power Supply will be tested in order to assess the effective improvement of the performances in comparison with the previous configuration. Aim of the thesis will be to contribute to the preparation and conduction of the tests, analyzing the results also with the aid of circuit simulations and comparing them with measurements from the past shots.

Competenze necessarie per svolgere con successo la tesi: Basic concepts of electrical engineering, MATLAB or Python, Simulink.

Data della proposta: 31/03/2023

Study of High voltage Power Supply systems of ECRH system for DEMO project.

RFX Supervisor: Marco De Nardi, Mauro Recchia

Academic supervisor: P. Bettini (TBC)
Head of the RFX research group: E. Gaio

Leader of the RFX research program: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa, modelling

Abstract:

The Electron Cyclotron Resonance Heating (ECRH) is presently selected as the reference Heating and Current-Drives (HCD) system for DEMO, the first power plant to demonstrate the feasibility of the electricity production with fusion energy.

The ECRH system design is based on gyrotrons, microwave generating vacuum tubes exploiting the interaction of a high energy electron beam with dc magnetic field in a resonant cavity. For the DEMO application the target microwave power of each gyrotron is 2MW and several tens of gyrotrons will be employed in ECRH system.

The gyrotron is characterized by different electrodes to accelerate the beam which are properly dc polarized by a dedicated High Voltage Power Supply (HVPS) system.

The HVPS is a modular system; the basic unit is the so-called  HVPS set,  which supplies a couple of gyrotrons. Each HVPS set is composed of:

  • one Main High Voltage Power Supply (MHVPS), a high power dc PS which provides the main power and the high voltage for the acceleration of the electron beam to the couple of gyrotrons;
  • two Body Power Supply (BPS), one for each gyrotron, low power high voltage dc PS which enhances the acceleration of the electron beam and provides control of the gyrotron output power

The analysis of the actual DEMO ECRH system operational scenario pointed out highly demanding active power profile on the ac network which does not fully respect the limits imposed for the interface with the Power Transmission Grid (PTG). In this regard in 2022 studies on the possibility to meet the PTG requirement by exploiting a suitable Energy Storage System (ESS) to smooth the power demand have been started.

The proposed activities foresee the study of the ECRH HVPS system of DEMO, the development of a circuital model of individual MHVPS and BPS and the simulation of their combined operation on an equivalent load representing the gyrotron.

The model will be extended to the HVPS set and numerically simulated to reproduce the current and voltage waveforms on the ac side, calculate the relevant absorbed power and harmonic content and extrapolate these results to the overall DEMO ECRH system.

On the basis of the results, preliminary studies on provisions to minimize the impact on the PTG will be performed.

Previous experience: Electrical engineering, analysis of linear circuits, basic knowledge of programming tools (Matlab or Python, Simulink, Psim)

Data della proposta: 31/03/2023

A deep-learning approach for the analysis of calcium signal in the characterization of the biological response of plants to external stimuli

Proponente/Relatore RFX: A. Rigoni-Garola, V. Antoni

Relatore accademico: G. Serianni

Capogruppo RFX: C. Taliercio

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The calcium ion plays a key signaling role in plants and is involved in a wide range of physiological processes such as growth, development and response to stress. Recent studies have shown that plasma activated water (PAW) treatment can lead to increased intracellular calcium levels in plants, which in turn activates various signaling pathways involved in plant growth and stress tolerance. The aim of the thesis is to organize in a single database the calcium signals expressed by different individuals of the same botanical species exposed to different PAWs. In particular, the different PAWs will correspond to exposure to two different plasma sources (torch and dielectric barrier discharge) and for different activation times. The database thus obtained will be subsequently analyzed using a machine learning algorithm so as to be able to detect the average characteristics of the calcium signals that emerge from the response of single individuals.

The work plans to identify and evaluate various models suitable for signal analysis and classification; a non-supervised approach is proposed. Starting from the experimental data, a database will then be built, suitably recorded so that the signals are compatible with the input to the models and subsequently the database will be analyzed to extract the main characteristics by comparing them with the known characteristics. The entire thesis work will be carried out in a python and jupyter environment, while the tools used will be Pandas for the creation of the data database and TensorFlow or Pytorch for the definition of the ML model

Competenze necessarie per svolgere con successo la tesi: Knowledge of the python programming language and a certain familiarity with the GNU-linux environment are recommended

Data della proposta: 31/03/2023

Simulation of plasma parameters towards the optimization of first wall components by Glow-Discharge Cleaning

Proponente/Relatore RFX: S. Ciufo, R. Milazzo

Relatore accademico: M. Zuin

Capogruppo RFX: L. Carraro

Responsabile di Programma RFX: L. Marrelli

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The Glow-Discharge Cleaning (GDC) is one of the most important technique for wall conditioning in fusion experiments. It is usually employed by considering only the current required for sputtering on the first wall materials and with relatively high voltages. The purpose of this thesis is to adapt a Particle-In-Cell (PIC) code in order to simulate plasma-wall interactions from the perspective of the RFX facing Carbon tiles. In particular, energy distribution and impact angles are quantities that must be estimated, depending on boundary conditions, so to serve as input for modeling solid-state phenomena (sputtering, impurity retention/desorption, defect generation, etc.) that determine fusion performance in turn. The importance of this study lies in gaining understating of the physics ruling plasma-wall interactions and the correct application of boundary condition. In this way, GDC operations can be significantly optimized by reduction in the resources required for the operation and in the time required for execution. The candidate’s thesis will focus on adapting the PIC code to create a map enclosing energy and angles for different species contained in the plasma and with respect to the facing wall. Results will be analysed to describe plasmas and they will deal with graphic visualization of the abovementioned parameter space with final aim of better understanding the dynamics of plasma-wall interaction. The work will take place at Consorzio RFX.

Competenze necessarie per svolgere con successo la tesi: Basic knowledge of Plasma and Solid State Physics, basics of coding and analysing software

Data della proposta: 31/03/2023

PL Threshold studies in the JET tokamak

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Motivation: Radiation control in D, T, and DT baseline plasmas is being reviewed [L. Piron 2022 SOFT papers submitted]. The discharges last longer when the optimal gas-fueling recipe combined with the use of pellet injection (ELM control) have been used. However, the discharges in T and DT suffer from radiation issue in a faster time scale w.r.t. to D ones. Why?

Strategy:

Investigate PLH transition metrics in D,T,DT plasmas performed in 2021

Compare the results with real-time metrics

Design experiments for DTE3 campaign

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Stability analysis of SMART equilibria using MARS-F

Proponente/Relatore RFX: L. Piron, E. Viezzer (University of Sevilla)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The main goal of the SMART tokamak is to explore the prospects of Negative Triangularity shaped plasmas for a future fusion power plant (FPP) based on spherical tokamaks. Although NT plasmas offer some attractive features for a future FPP, they are also typically more prone to magnetohydrodynamic (MHD) fluctuations. In this work, the MHD code MARSF will be used to explore the stability of SMART plasmas with positive vs negative triangularity. This Thesis project can be performed within the ERASMUS+ program.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Resonant field amplification in JET high pressure scenarios

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In magnetic fusion devices to probe plasma stability, magnetic field perturbations induced by means of external coils are applied in high pressure regimes in the so-called resonant field amplification technique. Such a technique has been extensively applied in high-beta plasmas performed in the JET tokamak (Culham, Oxfordshire, UK). In this project, data from multiple diagnostics, such as magnetics, Thomson scattering, and equilibrium reconstructions will be analyzed to characterize the plasma amplification process.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Modeling and simulation of Alfvén instabilities and zonal structures in tokamak plasmas

Proponente/Relatore RFX: L. Piron, A. Biancalani (University of Paris)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Tokamak plasmas are an example of systems where the dynamics is intrinsically multiscale. Microscopic turbulence generated by the gradients of the plasma temperature coexists with meso-scale

zonal flows (nonlinearly generated by the turbulence, analogously to the latitudinal bands in Jupiter) and meso-scale / macro-scale Alfvén instabilities.

Understanding the dynamics of zonal structures is particularly important because they have a crucial role in decreasing the turbulence levels. Recently, it has been seen that zonal structures can also be excited by Alfvén instabilities. Consequently, this has been proposed as a possible new mechanism for explaining the reduction of turbulence observed in experiments (see for example [1]).

Starting date: March 2023.

Duration: 6 months.

This paid internship has a maximal length of 6 months, to start in March. The topic is developed in the framework of the Eurofusion projects TSVV10 and ATEP. In this internship, the student will study the Alfvén instabilities in experimentally relevant configurations and estimate the amplitude and spatial structure of the zonal structures nonlinearly driven by these Alfvén instabilities.

References:

[1] A. Biancalani, A. Bottino, A. Di Siena, O. Gurcan, T. Hayward-Schneider, F. Jenko, P. Lauber, A. Mishchenko, P. Morel, I. Novikau, F. Vannini, L. Villard, A. Zocco, “Gyrokinetic investigation of Alfven instabilities in the presence of turbulence”, Plasma Phys. Control. Fusion 63, 065009 (2021)

Competenze necessarie per svolgere con successo la tesi: The student who wishes to apply should be in the M2 year, and should have a good knowledge of plasma physics and programming languages (Matlab or Python).

Data della proposta: 31/03/2023

Magnetohydrodynamic stability analysis of the pedestals of ASDEX Upgrade plasmas

Proponente/Relatore RFX: C. Angioni (IPP)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The high confinement mode (H-mode) dramatically improves the confinement properties of present tokamak plasmas and is therefore the scenario envisioned for future fusion reactors. The main characteristic of this scenario is the formation of a pedestal at the edge of the plasma by means of a transport barrier. The height of the pedestal is limited by the onset of edge localized modes (ELMs), quasi-periodic explosive instabilities at the plasma edge which expel particles and energy on millisecond time-scales. While ELMs in present day machines pose no danger, when scaled to a fusion reactor device they are predicted to cause significant damage to the machine components. As such, the understanding and exploitation of alternative regimes with high confinement but without ELMs is of significant interest. The onset of an ELM can be described by magnetohydrodynamic (MHD) stability codes.

This project involves the automation of a workflow which runs codes to test the pedestal MHD stability (such as MISHKA) starting from a standardized set of experimental information. Once this workflow has been implemented it should be applied to a database of experimental data from the ASDEX Upgrade tokamak to study the properties of the pedestal in ELMing and different ELM-free regimes. It is particularly important to provide an estimate of the distance to the MHD stability boundary in the various ELM free regimes to understand how robust these regimes are and the margin a given regime has before a large ELM is triggered.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Integrated core scrape-off layer modelling of JET deuterium-tritium baseline plasmas

Proponente/Relatore RFX: L. Garzotti (UKAEA)

Relatore accademico: . Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

JET performed a deuterium-tritium (DT) campaign in 2021 producing record fusion power and a wealth of experimental data for analysis and interpretation. One of the most important aspects to be investigated is the combined dynamics of the core and the scrape-off layer of the plasmas produced in DT, which is responsible for their confinement properties, the interaction with the first wall, the fueling requirement and, ultimately the performance in terms of fusion power. The proposal for this thesis work is to model a limited set of JET DT plasmas with state-of-the art integrated modelling codes to investigate the physics of the phenomena above mentioned. Initially the work will be limited to one of the aspects of the plasma phenomenology to progressively include more of them if time allows it.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Diagnostic Data Integration Using Deep Neural Networks for Real-Time Plasma Analysis

Proponente/Relatore RFX: L. Piron, A. Rigoni Garola

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In this project, deep neural networks will be applied for diagnostic data integration in the complex scenario of the active control for magnetically confined fusion plasmas.

A database of 60000 signals acquired by the Soft-X-Ray diagnostic in the RFX-mod experiment will be analyzed to reconstruct plasma temperature profiles.

The network topology called variational auto encoder (D. P. Kingma and M. Welling, “Auto-encoding variational Bayes,” in Proc. 2nd Int. Conf. Learn. Represent. (ICLR), Banff, AB, Canada,Y. Bengio and Y. LeCun, Eds., Apr. 2014. http://arxiv.org/abs/1312.6114) will be adopted to add useful information to the reconstruction of the missing temperature points.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Development of a Wall Conditioning system for the SMART tokamak

Proponente/Relatore RFX: E. Viezzer

Relatore accademico: L. Piron

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Wall conditioning is key to improve the plasma performance in a magnetically confined fusion reactor as impurities released from the wall can cool down the plasma until its collapse. Several methods are typically used to condition the reactor wall, and, among others, in this work glow discharges and boronization will be explored as main wall conditioning methods for the SMART tokamak. The Thesis project can be performed within the ERASMUS+ program.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Characterization of magnetic field errors in MAST-U coil manufacturing

Proponente/Relatore RFX: L. Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Error fields are spurious magnetic field perturbations that can degrade the plasma performance in magnetic fusion devices through various mechanisms, such as rotation braking, fast particles losses and MHD instability onset. The identification of error field sources thus plays a vital role to guarantee safe and robust plasma operations. In this project, the validation of a 3D electro-magnetic modelling of poloidal field coils again experimental data will be carried to detect error field sources in the coil manufacturing process in the MAST-U device (Culham, Oxfordshire, UK).

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Assessment of the concept feasibility of spin-offs from magnetic fusion research

Proponente/Relatore RFX: L. Piron, P. Martin

Relatore accademico: L.Piron, P. Martin
Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Interest on magnetic fusion energy research has rapidly evolved over the years according to the need of developing new energy technologies able to fulfil the increase energy demand, while not impacting on the global climate change. The goal of harnessing the magnetic fusion energy indeed is to produce power for mankind which is virtually unlimited, intrinsically safe and completely free of any greenhouse gas emissions and radioactive waste.

Given its complex, multidisciplinary nature and tantalizing challenge posed, it should be no surprise that magnetic fusion energy research has driven numerous spin-offs, which are proposing to contribute on fusion research on the way to fusion electricity.

The aim of this project is to perform a concept feasibility study of magnetic fusion spin-offs, by reviewing the state of the art for spin-offs fusion applications.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Analysis of locked dynamics in MAST-Upgrade / JET / AUG

Proponente/Relatore RFX: Lidia Piron

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Locked modes are MHD instabilities which can be present in magnetic fusion devices and are responsible of rotation braking, particle and energy confinement degradation, and can lead to plasma disruptions. Because of these deleterious effects, the dynamics of locked mode (triggering and its evolution) needs to be deeply investigated.

In this Thesis work, experiments performed in Work Package Tokamak Exploitation (WPTE) devices, which suffer from the presence of locked modes, will be analyzed utilizing data from multiple plasma diagnostics.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Analysis of disruption paths in TCV via Machine Learning

Proponente/Relatore RFX: L. Piron, A. Pau (EPFL)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In the last years, data science methods from the fields of machine learning and artificial intelligence (ML/AI) have offered several opportunities for accelerating the progress towards the realization of fusion energy. The massive amount of data available from current operating tokamaks, together with the exponential growth of computing and cloud technologies, have enabled new scenarios in the framework of advanced data analysis and processing. The work proposed for this Master Thesis fits in different priority research opportunities in Fusion, where “Data-enhanced Physics Informed Prediction” is one of the emerging topics and deals with, among the other things, plasma state monitoring, exception handling, off-normal events, and disruptions.

Disruptions are a catastrophic loss of plasma thermal and magnetic energy potentially causing severe damage to the machine and they represent one of the main concerns for the exploitation of the tokamak concept in future fusion power plants. The proposed work will focus on the development of a hybrid framework (data-driven and physics-based) for predicting and reacting to the most common precursor of disruptive terminations in the TCV Tokamak, such as MHD instabilities and Vertical Displacement Events (VDE). The prediction of such events, combined with model-based approaches, can improve the response of the Plasma Control System, and help in designing and optimizing plasma termination schemes. The proposed activities have also a direct connection with the Task of the ITPA MHD, Disruptions and Control Topical Group dealing with the design of the trigger generation function and control logic for the ITER Disruption Mitigation System, and with the EUROfusion Work Package for Tokamak Exploitation (experiments on this specific topic are planned for 2023).

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Advanced locked mode detection in the TCV tokamak

Proponente/Relatore RFX: L. Piron, A. Pau (EPFL)

Relatore accademico: L. Piron

Capogruppo RFX: D. Terranova

Responsabile di Programma RFX: T. Bolzonella

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

In the last years, the exponential growth of computing and cloud technologies, have enabled new scenarios in the framework of advanced data analysis and processing. A large amount of high-dimensional data is produced daily by many diagnostics systems measuring various plasma properties during the experiments. One of the most important systems in a Tokamak is the set of magnetic sensors used to monitor Magnetohydrodynamic (MHD) activity and detect onset and development of MHD instabilities potentially causing a disruption. Disruptions are a catastrophic loss of plasma thermal and magnetic energy potentially causing severe damage to the machine, and they represent a key research priority in the fusion roadmap. MHD instabilities are often seen as precursors to disruptions. The detection of these modes can be used to predict disruptions and is routinely used in different machines (such as in the JET tokamak) to trigger the disruption mitigation system.

MHD modes, often rotating, can stop rotating (mode locking) with respect to the plasma frame, leading eventually to disruption. The slowing down of the mode rotation velocity as well as the amplitude of the locked mode can be detected respectively by measuring the oscillating field perturbation in tangential field pick up coils or Mirnov coils, and the effective amplitude of the radial component of the mode based on saddle coils measurements.

The presence of vacuum field pickup, misalignment between sensors and axisymmetric coils, DC & AC coupling between coils and sensors can pollute the measured plasma 3D field, making MHD mode detection challenging. One of the objective of this thesis is to develop and implement real-time algorithms to remove unwanted component through AC and DC compensations (such as in https://aip.scitation.org/doi/pdf/10.1063/5.0101630) and derive a robust locked mode detector for the TCV Tokamak. An additional objective would be to compare the locked mode amplitude to trigger a disruption in TCV with the scaling proposed in https://iopscience.iop.org/article/10.1088/0029-5515/56/2/026007#references.

Competenze necessarie per svolgere con successo la tesi:

Data della proposta: 31/03/2023

Optimization of the magnetic field in a RF plasma source experiment in support of SPIDER operation.

Proponente/Relatore RFX: N. Marconato, A. Pimazzoni

Relatore accademico: N. Marconato
Capogruppo RFX: M. Brombin

Responsabile di Programma RFX: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The student will work for the numerical optimization of the shape of a particular coil winding. The aim is to reproduce the magnetic field of the SPIDER experiment in a new small scale experiment for test on the Radio Frequency (RF) driver operation. Of primary importance is indeed testing the effect of the magnetic field on the efficient operation of the RF driver. Therefore, flexibility in the generation of magnetic field topology would also be adviced.

The design optimization will be carried out with electric and magnetic model in the commercial FEM software Comsol. Mechanical analyses will be also required for estimating the actual mechanical stress to be withstood.

Competenze necessarie per svolgere con successo la tesi: Basic concepts of electrical engineering. FEM knowledge is welcome.

Data della proposta: 31/03/2023

Design of a test-bed for High Voltage tests of gas insulted components.

Proponente/Relatore RFX: N. Marconato

Relatore accademico: N. Marconato
Capogruppo RFX: M. Brombin

Responsabile di Programma RFX: S. Peruzzo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

The student will work for the numerical optimization of the shape of electrodes and the insulator of a mock-up system used for experimental tests on High Voltage (HV) gas insulated components. This activity is part of the R&D for the design of a HV transmission line feeding the Neutral Beam Injector (NBI) of the DTT fusion experiment.

The design optimization will be carried out with a sophisticated FEM model specifically implemented in Comsol. Comparisons with simpler models will also be required for validation.

Competenze necessarie per svolgere con successo la tesi: Basic concepts of electrical engineering. FEM knowledge is welcome

Data della proposta: 31/03/2023

Design of in vessel pick up coils for DTT fusion experiment

Proponente/Relatore RFX: N.Marconato, T. Patton

Relatore accademico: N. Marconato
Capogruppo RFX: M. Brombin

Responsabile di Programma RFX: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

L’esperimento SPIDER (https://www.igi.cnr.it/ricerca/negative-ion-neutral-beam-injection/spider/i-componenti-di-spider/) è in shut-down fino a dicembre 2022 per le riparazioni, le modifiche e i miglioramenti derivanti dall’esperienza fatta nei primi anni di funzionamento dal 2018 ad oggi.

Tra questi upgrades è prevista l’installazione della diagnostica detta “Beamlet Group Current Monitor” (BGCM) per la misura della corrente del fascio di particelle relativa a ciascuno dei 16 gruppi di aperture (beamlet groups) delle griglie di accelerazione. È necessario pertanto progettare un sensore di corrente in grado di misurare la corrente del fascio in uscita dalla griglia di terra per ciascuno dei 16 bealmlet groups. I 16 segnali di corrente derivanti da ciascun sensore daranno la misura della totale corrente di fascio, permettendo inoltre una valutazione dell’uniformità dello stesso.

Principali requisiti del sensore di corrente sono i seguenti:

•  Misura sia della componente DC, sia della componente ad alta frequenza (decine di kHz);

•   Operazione in alto vuoto (10-6 mbar);

•   Resistenza a carichi termici non trascurabili;

•    Elevata risoluzione e precisione in un range di correnti compreso tra 100 mA e 3 A;

•    Immunità a campi magnetici DC esterni;

•    Immunità alla componente a radiofrequenza di 1MHz della corrente del fascio;

•    Immunità a breakdown elettrici

•    Compatibilità meccanica con gli spazi disponibili davanti a ciascun beamlet group.

La tecnologia dei cosiddetti Direct Current Current Transformer (DCCT) è ritenuta essere la più promettente per questo tipo di sensori di corrente, da un punto di vista di sensibilità, robustezza ed immunità ai disturbi. La tesi proposta si pone all’interno delle attività necessarie allo sviluppo di un sensore che adotti questa tecnologia per il caso specifico di SPIDER.

Allo studente è richiesto il supporto per l’ottimizzazione di modelli numerici, sia circuitali che agli elementi finiti tridimensionali, sulla base di dati sperimentali ottenuti su primi prototipi del sensore. L’attività è utile da una parte per un’avanzata comprensione dell’effetto delle non idealità nel segnale ottenibile dal sensore e dall’altra per una precisa modellazione del sensore finale, sia da un punto di vista della sua struttura fisica, sia per quanto riguarda l’elettronica di pilotaggio e readout. L’attività è molto urgente.

Competenze necessarie per svolgere con successo la tesi: Basic concepts of electrical engineering. Fair knowledge of the English language Electronics and FEM knowledge is welcome

Data della proposta: 31/03/2023

Commissioning and first measurements of a new ICP discharge experiment at the Neutral Beam Test Facility

Proponente/Relatore RFX: I. Mario

Relatore Accademico: E. Sartori

Capogruppo: A. Rizzolo

Responsabile di Programma: V. Toigo

Tipologia: Sperimentale, Teorica, Numerica, Compilativa

Abstract:

Neutral Beam Injectors for fusion applications require the production and acceleration of negative ions. Negative ion sources are based on the inductive coupling of electromagnetic waves to a hydrogen plasma (ICP discharge). To optimise the design of such sources, and particularly of the RF driver (the region where the plasma is generated), the MINION experiment is under design at Consorzio RFX and will start operations in 2023.

The first experimental phase will be devoted to plasma ignition itself and will require commissioning and testing of the various plants (vacuum, cooling, power supplies). The main outcome should be the identification and optimization of a reliable start-up process for the plasma.

The student will improve his/her knowledge of the behaviour of ICP plasmas including ignition and plasma characterization.

Measurements of the plasma properties with optical system and Langmuir probes will be performed, aiming at characterize the spatial distribution of the plasma parameters in the ion source, as well as electrical measurements at the RF circuit to derive the coupling efficiency and to compare different confinement configurations realised by arrays of permanent magnets.

Depending on the student preferences and on the experimental needs, the student may perform numerical simulations of the plasma discharge, or design activities aiming at the improvement of the device, (e.g. development of an electric circuit to produce a uniform filter field).

Data della proposta: 01/07/2023

Caratterizzazione numerica (e sperimentale) dei forni del cesio per SPIDER

Proponente/Relatore RFX: Sartori (Fadone)

Relatore Accademico: E. Sartori
Capogruppo: A. Rizzolo

Responsabile di Programma: D. Marcuzzi

Tipologia: Sperimentale, Teorica, Modellistica, Compilativa

Abstract:

Gli iniettori di neutri sono riscaldamenti ausiliari fondamentali per le macchine da fusione nucleare: la formazione del fascio di ioni negativi, precursore del fascio di neutri, avviene estraendo ioni negativi da un plasma di idrogeno. Poiché in una scarica di idrogeno la densità di ioni negativi è molto bassa, va massimizzata grazie alla evaporazione di cesio, che ricoprendo le superfici metalliche affacciate al plasma, ne riduce la funzione lavoro; pertanto, atomi di idrogeno che impattano sulla superficie possono estrarre un elettrone dalla superficie e venire riemessi come ioni negativi.

Dato il ruolo fondamentale del cesio nella produzione di ioni negativi, l’uniformità del fascio risultante dipende dalla uniformità della copertura di cesio, specialmente alle superfici vicine ai fori da cui il fascio viene estratto. L’esperimento “CATS” è equipaggiato con varie diagnostiche dedicate alla caratterizzazione della quantità di cesio evaporato, della distribuzione angolare della emissione dal forno, della probabilità di deposizione (sticking) e della funzione lavoro delle superfici esposte al vapore di cesio.

Lo studio proposto consiste 1) nella misura tramite un detector mobile Langmuir-Taylor della distribuzione spaziale del cesio emesso, e 2) della quantità evaporata al variare della temperatura del forno; 3) nella stima dello sticking del cesio alle superfici della camera, sfruttando la microbilancia e le altre diagnostiche 4) nel confronto con modelli numerici dei risultati del nuovo ugello di evaporazione all’interno della camera da vuoto di CATS.

E’ possibile adattare il progetto di tesi a seconda del tempo a disposizione e delle preferenze dello studente, anche includendo attività sperimentale sulla sorgente SPIDER.Competenze richieste (se necessarie):

Data della proposta: 01/12/2023

Contatti per richieste e informazioni

Gli studenti interessati ad una delle tesi disponibili possono contattare
il coordinatore delle attività di tesi Prof. Leonardo Giudicotti (leonardo.giudicotti@unipd.it).

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