Plasma edge turbulence probing and feedback control and stabilization experiments

Abstract

Experiments in modifying plasma edge turbulence were carried out on the Texas Experimental Tokamak (TEXT) by launching waves using two electrostatic probes in the shadow of the limiter. Measurements indicate that the wave, launched with a typical frequency range of 15 to 50 kHz from the edge of the machine top, is received by sensing probes located halfway around the torus. The detected signal strength depends weakly on the frequency of the wave and on the phasing of the applied AC signal between the launching probes. Modifications to the spectrum of the edge potential fluctuations are observed at the launching frequency. These experiments have been extended to the control of the edge plasma fluctuation level using feedback. The launcher is driven by the floating potential of the fluctuating plasma at the location of the launching probes. Edge fluctuations are reduced or excited, depending on the phasing between the launching probes, both locally and at the downstream sensing probes. The fluctuation induced particle flux as well as the local plasma parameters are affected by feedback phasing