First experimental results of runaway beam control in TCV

The first attempts of suppression of runaway electron (RE) beams in TCV are presented. Disruption-generated RE are obtained through small injections of high-Z impurities (Ar and Ne) in lowdensity inner limiter circular plasmas (Bt=1.43 T, Ip=200 kA). The gas injection is performed using the disruption mitigation valve system. A dedicated controller for RE suppression is implemented in the digital plasma control system. The current quench (CQ) and the RE plateau onset are detected by feeding Ip to an approximate derivative linear filter with specific logic. Once the RE plateau onset is detected, a new Ip reference, ramping-down to zero with a pre-selectable rate, replaces the standard reference. To improve the ramp-down tracking performance, a further logic block, implementing a novel double integrator scheme, is paired with the standard plasma current controller to select the appropriate voltage for the amplifiers powering the ohmic coils. The RE beam has a slow radial outward shift during the plateau phase of the order of 0.15 m, but the position control system is able to avoid RE interactions with the vessel before the RE final loss.