22 / 2021-04-09 01:09:12

3D magnetic fields/topology effects on MHD instability and turbulence transport

low frequency oscillation,tuebulence modulation,plasma flow modulation,megnetic island

Understanding of plasma transport is one of the most important issues in present magnetic confinement fusion researches. The transport beyond the well understood neoclassical mechanism is termed as anomalous and the turbulence is considered to be the major candidate underlying such a process. Previous studies show that the turbulent transport could be influenced by modulation of the turbulence and also the plasma flow with the presence of macro-scale MHD modes.  Therefore it is significant to investigate the potential physics of those kind of modulation and  so as to optimize the plasma performance.

Wendelstein 7-X (W7-X) is optimized for reduced neoclassical transport and it is suitable to investigate the turbulent transport. A 1-2kHz low frequency oscillation is frequently observed by multiple diagnostics during the island divertor operation of W7-X. In this work, this low frequency quasi-coherent electromagnetic oscillation is studied based on the plasma in the standard configuration (edge iota=1) via the measurements of poloidal correlation reflectometer (PCR) .  It is located outside the last closed flux surface and it contributes to both the turbulence modulation and velocity oscillation in the scrape-off layer (SOL) and island region.  Furthermore, the application of external control coils which will adjust the island size and position,  goes along with a significant modification of magnetic topology at the edge. Simultaneously, this low frequency oscillation undergoing corresponding evolution with different control coils currents.  It is interested to study the dynamics between those two phenomenons. The comparison of the low frequency oscillation behaviors under different control coils currents scan will be shown in detail.