EDGE PLASMA PROPERTIES OF OHMIC DISCHARGES WITH RESONANT MAGNETIC PERTURBATIONS IN THE STOR-M TOKAMAK

Abstract

Understanding and controlling cross-field transport caused by turbulence is a major challenge towards achieving the plasma confinement necessary to operate a thermonuclear fusion reactor. Measuring fluctuations of plasma density and potential in the edge of a toroidally confined plasma is important to characterize the turbulent transport and suppression mechanisms for turbulence. A 16 pin rake probe is installed on the Saskatchewan Torus-Modified tokamak to measure density and potential with high temporal resolution. The array consists of 8 by 2 single Langmuir probes, which allow good radially and limited poloidally resolved measurements. Profiles of various plasma parameters were constructed for the edge and scrape off layer (SOL) to investigate different discharge scenarios. The Resonant Magnetic Perturbations altered the plasma transport in the edge and SOL region, leading to a higher density pedestal and a potential drop in some cases. During an enhanced confinement phase, it was possible to identify a region where intermittent transport events are created and leave behind holes of lower density. The existence of the high-frequency branch of zonal flows, the geodesic acoustic mode, could not be verified conclusively. Increased coherence and amplitude of floating potential fluctuations in the frequency range of f ≈ 20 kHz were found, but coherent Magnetohydrodynamic (MHD) oscillations indicated a substantial connection to the floating potential fluctuations in this frequency band, while MHD oscillations at higher frequency showed no connection.