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Description
The ITER fusion reactor will be heated by fast neutral beams generated by accelerating and neutralizing negative ions, produced in a RF inductively-coupled plasma and expanding through a region featuring a magnetic filter. Since the beginning of SPIDER operation in 2018, many issues have been solved, lessons learned and objectives reached, but fixing several major problems requires a long shutdown, started at the end of 2021, in which the whole plasma source and accelerator will be dismounted. In this phase additional modifications with respect to the original design will be introduced in order to improve the system performance, driven by the experience acquired in the last years. These include the addition of further sets of permanent magnets in the plasma source expansion chamber and around the RF drivers, with the aim of improving the plasma confinement and consequently its density and possibly its uniformity.
The present paper reports the results of numerical studies of the plasma parameters in SPIDER source with different types of modifications of SPIDER device including new permanent magnets configurations. Analysis are done by means of the numerical code FSFS2D in which a self-consistent two-dimensional fluid description of the source, including neutral gas flow, plasma chemistry, RF-plasma coupling in the driver and plasma transport through the magnetic filter has been implemented. The different particle species (electrons, H
In order to partially account for the 3D flow pattern within our 2D model, simulations are done in two geometrical situation, in the vertical plane with the magnetic filter being perpendicular to the integration domain and in the horizontal plane with the filter field in the integration surface. Preliminary results indicate, that the permanent magnets around the RF driver tends to increase the plasma density in the driver. The influence of the magnetic fields on the negative ion currents in the expansion zone is also investigated.
