Reaction of turbulence at the edge and in the center of the plasma column to pulsed impurity injection caused by the sputtering of the wall coating in L-2M stellarator

Abstract

Impurity injection into plasma caused by the sputtering of the wall coating in the L-2M stellarator during auxiliary electron cyclotron resonance heating leads to a change in the level of plasma density fluctuations with frequencies above 0.25 MHz: suppression of long-wavelength (k ⊥ = 2 cm–1) density fluctuations in the edge plasma, intensification of short-wavelength (k ⊥ = 30 cm–1) and long-wavelength (k ⊥ = 1 cm–1) fluctuations at the midradius of the plasma column, and intensification of short-wavelength fluctuations (k ⊥ = 20 cm–1) in the plasma center (including the gyroresonance region). At the same time, the level of fluctuations with frequencies below 0.25 MHz remains unchanged. In the edge plasma, a decrease in the plasma potential and suppression of its fluctuations is observed during impurity injection, which also causes an increase in MHD activity.