Source for Production of Ion of Deuterium Extracted from Rf plasma
SPIDER: THE WORLDS MOST POWERFUL
NEGATIVE ION SOURCE
To heat the plasma of ITER and future fusion reactors, millions of watts of power can be input using neutral particle beam injection (NBI).
NBI is the real “workhorse” among ITER’s external heating systems.
Due to its extreme complexity, however, it requires an extensive research and development program, in particular on the most critical component: THE NEGATIVE ION SOURCE.
The research and development on physics and technology related to the ion source for ITER are developed in Padua on SPIDER, the first of the two test prototypes housed in the NBTF plant.
SPIDER is aimed at demonstrating that all the complex systems of which it is composed and which control the source and the particle extraction phase can operate synergistically.
Its peculiarity comes from the presence of sophisticated diagnostic systems that allow the measurement of the parameters of the generated beam, the study of its operation and its fine-tuning.
SPIDER is in operation since 2018
The SPIDER operation began on 11 June 2018 – when the Director-General of ITER pressed the button that started the ignition of the hydrogen plasma in the ion source for the first time, lighting up the SPIDER room for a few seconds.
In the following months, researchers focused on optimizing and controlling analogue plasmas to maximize power transfer on ionized gas through radio frequency generators.
The combined use of 8 antennas connected to the generators allowed the team to increase the power transmitted to the plasma by about 10 times the power achieved during the first plasma, reaching 320 kW. This was possible thanks to the progressive increase in the gas pressure profile, a greater understanding of the behavior of the radiofrequency generators and an overall improvement of the entire control system.
The experimental focus then shifted to the extraction and acceleration system.
The system consists of a series of three electrode grids, each with 1280 holes through which the negative particles generated in the plasma are extracted and accelerated using a potential difference applied to the grids of increasing intensity.
Towards the end of 2018, the second grid – called the Extraction Grid Power Supply (EGPS) – was used for the first time. Since then, a large stream of particles (mainly electrons) has been extracted from the plasma with a acceleration to a few kilovolts. The capacity of the high current holding system was checked in parallel with and the installation of diagnostic systems: the STRIKE calorimeter and spectroscopy lines for visible light.
The third and last electrode (gray) of the acceleration system was finally operated in spring 2019, at a potential of 30 kV compared to the second with the formation of a fast beam of negative hydrogen ion particles.
Lets see how the prototype of the negative ion source works, with a virtual voyage inside SPIDER
DESCRIPTION OF THE PARTICLES INVOLVED