Active feedback stabilization of flute instability in a mirror trap

Summary form only given. Axi-symmetric mirror machines are the simplest magnetic confinement devices, and as such could be attractive for fusion machines, ions separation, and more. However, mirror machines suffer from particle loss due to the violent flute instability. We demonstrates for the first time the stabilization of fast growing, slowly rotating flute instability by multi-input, multi-output active feedback system.The feedback system consists of six optical probes, digital signal processor, and six needle electrodes. Step response and MHD spectroscopy indicates a non-linear response of the plasma to the electrodes due to the sheath-limited electrodes' current. This makes the feedback unstable at short time scales, but stable on longer times. Using local feedback algorithm, we demonstrates a large suppression of m=1 mode and significant simultaneous suppression of m=1,2 modes. Higher spatial and temporal components of the flute instability are slightly enhanced by the feedback, but are passively stable due to finite Larmor radius effect.