Feedback experiments on a high-energy plasma in the Phoenix mirror machine

Abstract

Experiments using a single feedback loop, in which electrostatic signals from a plasma were amplified and fed back as potentials to the plasma boundary, have been carried out in the PHOENIX-II mirror machine working as a simple mirror. The effect of the feedback system on plasma losses caused by the flute instability has been studied and a correlation between plasma losses and the amplitude and frequency of the instability has been obtained. It is concluded that plasma losses can be controlled, to a certain extent, by a simple feedback system.

Research on open traps in the Soviet Union

“…Nevertheless, complete stabilization is attainable if the right spatial structure is accorded to the feedback and the transfer coefficient of the electronic circuit has a specially synthesized amplitude-phase frequency characteristic. Significant results were achieved in this manner [8,9]: in particular, stability was obtained nature proved to be even more inventive than the imagination of theoreticians, and the second reliably discovered kinetic instability came as a surprise to them. We are referring here to the so-called modified negative-mass instability (MNMI) which appeared in PR-5 [13] and DCX-II (Oak Ridge) [14] in the form of powerful oscillations, exerting a very strong effect on the plasma and not explained by any of the existing theories.…”

Measuring drift velocity and electric field in mirror machine by fast photography

“…The first study of active feedback control of plasma instability [1] considered the use of many electrodes at the plasma's outer diameter to reverse the positive feedback. Early works applied active feedback to mirror traps with a major improvement of plasma density [2,3]. These experiments used electrodes to sense the plasma's electric field and other electrodes as actuators to feed back an external field.…”

Active feedback stabilization of the flute instability in a mirror machine using field-aligned coils

“…However, all these works used an analytical approach, assuming infinitesimal perturbation amplitudes, de-coupling of the various modes, and other simplifying assumptions. Few experimental efforts [5,6] demonstrated the possibility of active feedback control in mirror machines, but employed only electrostatic control, on an extremely lowdensity plasma. While progress in feedback stabilization of mirror traps has been very slow, active feedback has become a major tool for tokamaks and other toroidal traps.…”