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

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.