LOW FREQUENCY OSCILLATIONS IN U-2M CONDITIONING RF DISCHARGES

MHD oscillations were studied in low magnetic field (B-0 = 0.01 T) radio frequency discharges of the URAGAN-2M (U-2M) stellarator. Coherent oscillations are observed by bolometers, triple Langmuir probe microwave interferometer (140 GHz) and magnetic pick-up coils in different toroidal cross-sections of U-2M. Modified diagnostics show, that the plasma beta (beta= nT/(mu B-0(2))) is rather high in these discharges in spite of the low temperature (T-e = 10...50 eV) and density (n(e) = (0.5...1).10(12)cm(-3)) due to very low magnetic field. Variation of the magnetic configuration of U-2M substantially modifies fluctuations amplitude, oscillating modes type and frequency. Rotated m = 2 mode is transformed into the Sawtooth-like oscillations in different magnetic configurations. Strong dependence on the magnetic configuration indicates that observed in U-2M phenomena can have similar nature as in stellarator high temperature plasmas.