Power supplies for the stabilisation of plasma vertical position: recent upgrades and future development

The authors report on the improvement of the radial field amplifier (RFA) and on its subsequent positive effect on the plasma vertical stabilization. It is noted that the work carried out on the RFA has enabled an increase in reliability and performance. Full output voltage swings no longer lead to large circulating current excursions and subsequently to trips of the amplifier with loss of plasma vertical control. For small output voltage variations (amplitude <10% of the full range), the frequency bandwidth has been extended from 100 to 300 Hz and is still of 245 Hz for output voltage variations of 25% of the full range. As a result, the vertical stabilization of quiescent plasmas has been significantly improved and it was possible to obtain plasmas with increased X-point/wall gap as desired for the experimental program. However, extended capabilities of the amplifier are still required to avoid the saturation of the plasma vertical position feedback loop in some cases of highly elongated plasmas in the X-point configuration. A fast RFA having these extended capabilities is being designed