Effects of pellets and impurity injection on runaway control experiments on FTU

Introduction FTU is conducting an extensive program aimed at controlling and mitigating purposely generated runaway electron (RE) beams in natural and induced disruptions [1, 2]. During the latest experimental campaign different mitigation techniques have been tested, which involved injection of Laser Blow Off (LBO) metal impurities and of multiple Deuterium pellets (1÷2×1020 atoms). A large number of discharges has been analysed correlating various plasma signals to REs behaviour. The injections have been performed both during the plasma current flat top, with seed REs embedded in a hot plasma, and also after current quench (CQ), with current mainly carried by REs, in order to extrapolate information for ITER predictions. The main RE measurements used in this work were the following diagnostic systems: BF3 chambers, only sensitive to neutrons; NEU213 organic liquid scintillator, sensitive both to neutrons and hard X-rays (HXR); Gamma camera to measure HXR produced by the REs through bremsstrahlung in the plasma; Cherenkov probes to detect REs escaping the plasma [2,3].