Feedback stabilization of a plasma instability by a remote modulated source at the electron cyclotron resonance frequency

It has been demonstrated that the ion-sound instability can be stabilized by a remote feedback technique. The instability was sensed by a photo-diode detector outside the plasma, and the suppressor element was an electron-cyclotron resonance (E.C.R.) structure remote from the plasma. Power from this causes local heating of the electrons, and feedback is effected by modulation of the E.C.R. power level, at the instability frequency. A theory is developed which predicts the variation of the instability amplitude and frequency in terms of the change in electron temperature Delta T, fractional modulation of The E.C.R. power f and phase change in the loop phi . Comparison between theory and experimental measurement show good agreement.