RFX-mod2 (Reversed Field eXperiment)
originates from the results obtained by the RFX-mod
device that was in operation until 2016.
The experiment aims to study the physics of fusion plasmas and magnetic confinement in Reversed Field Pinch (RFP) configuration.
The challenge of this new machine is to be able to produce a plasma with much improved parameters compared to those of RFX-mod and to clarify whether the RFP configuration can represent a valid alternative to the tokamak design in the perspective of a future fusion reactor.
RFX-mod2 is a toroidal machine, i.e. in the shape of a doughnut, which uses the magnetic field to confine the plasma using the Reversed Field Pinch configuration, an alternative to the Tokamak, based on magnetic fields of lower intensity and only using the ohmic effect for heating the plasma.
Plasma is a very hot gas, brought to temperatures high enough that strip electrons from the gas atoms (usually Hydrogen or Deuterium atoms are used). The atoms that have lost electrons become ions, i.e. electrically charged atoms. Plasma is therefore a hot, rarefied and electrically charged gas that lends itself well to being confined by magnetic fields.
The new machine has a larger plasma volume which is also closer to the control systems. The sophisticated magnetic instability control system already installed on the RFX-mod experiment is one of the flagships of the laboratory, being the most advanced currently operating on fusion experiments. In RFX-mod2 it has been further improved. Thanks to these modifications, it is possible to more effectively control the energy losses connected to the interaction of the plasma with the chamber walls that contain it, obtaining more stationary Single Helicity states and warmer and better confined plasmas
The RFX-mod2 machine aims to complete the study of the properties of the RFP configuration in the plasma current regimes up to 2MA. To this end, modifications of some components of the machine are underway, in particular:
The purpose of these changes is twofold:
While the RFX and RFX-mod experiments were surrounded by a vacuum chamber characterized by a very high resistivity (Inconel 625), in RFX-mod2 a copper structure, of much lower resistivity, will be the conductive surface closest to the plasma. It will be protected by a wall made of graphite tiles, which is the first material surface seen by the plasma and built to withstand its power.
With this, several advantages are expected:
The improvement works were financed by the Veneto Region under the Por/Fesr research grants. The MIAIVO project, obtained in collaboration with the Industrial District of the upper Vicenza area, has brought in 2 million Euros of funding for research and development, slightly less than the half of the expected expense for completing all the upgrades.
| Maximum plasma current | 2 MA |
| Maximum plasma temperature | 20 M °C |
| Impulse duration | 0.5 s |
| Particles/m3 | ~ 5*1019 |
The magnetic confinement of fusion plasma is based on the fact that ions and electrons, charged particles, are forced to follow the magnetic field lines.
Several types of magnets are used to bring the RFX-mod2 experiment into an RFP configuration:
MAGNETIZING WINDINGS, which induce the poloidal field and plasma current
FIELD SHAPING (FS) WINDINGS, also called primary windings, which are meant to control the plasma equilibrium
TOROIDAL WINDINGS supply the toroidal component to the magnetic field
ACTIVE COIL SYSTEM, formed by 192 saddle coils positioned in 48 toroidal positions with 4 coils assigned to each position. This system provides a radial magnetic field.
The RFX-mod2 machine is formed by an ultra high vacuum support structure
(VTSS) which also includes the copper shell inside which the anisotropic graphite tiles are housed. These tiles form the first wall, the structure closest to the plasma, designed to support the high-power loads related to the interaction with the plasma. The VTSS provides mechanical support to the external coils and is equipped with 150 ports to allow access to the vacuum pump, gas supply and diagnostics system.
The vacuum chamber is housed in a support structure inside the experimental room of Consorzio RFX.
In order to study fusion plasmas, the RFX-mod2 experiment is equipped with an impressive diagnostic apparatus of which the main ones are:
