Effect of the transverse magnetic field on turbulence and parameters of a plasma column in the L-2M stellarator

The influence of magnetic configurations with magnetic hills or wells on th e parameters of a plasma column acid turbulence characteristics were studie d in experiments in which the plasma was created and heated by a microwave beam at the second harmonic of the electron cyclotron frequency. Calculatio ns show that, for [beta] = (1.5-2) x 10(-3), a configuration with a magneti c well takes place and the Mercier criterion for stability of the ideal MHD modes is satisfied. It is shown that the compensation of the Shafranov shi ft of the plasma column by a transverse (vertical) field (B-v/B-0 = 5 x 10( -3)) leads to a configuration with a magnetic hill in which the Mercier sta bility criterion is violated in the central region of the plasma column. It is experimentally shown that the stored plasma energy in the magnetic-hill configuration is reduced by one-half in comparison with the magnetic-well configuration. in the case of a magnetic hill, the energy of fluctuations i ncreases both in the plasma core and near the separatrix, and the quasi-reg ular components of the wavelet spectra grow. When the Shafranov shift is co mpensated only partially (B-v/B-0 similar to 3 x 10(-3)) and the system is near the instability threshold, the stored plasma energy and the central el ectron temperature are somewhat higher, and the radiation power of fast ele ctrons from non-Maxwellian tails at the second harmonic of the electron gyr ofrequency decreases. It is found that the wavelet spectra of fluctuations change, the coherence coefficient for spectral components increases, and th e radial electric field near the separatrix decreases. (C) 2000 MAIK ''Nauk a/Interperiodica".