Effects of equilibrium and stability of high beta RF heated plasmas in the URAGAN-3 torsatron

Systematic studies of currentless plasma produced in the URAGAN-3 torsatron by RF heating at ω < or approx. ωHi have led to the discovery of three types of discharge. The first type (called D-discharges) was encountered on working with bare, stainless steel, helical frame antennas. They were characterized by rather high densities (ne(0) ≤ 2x1013cm-3), moderate temperatures (Ti(0) ≤ 0.3 keV, Te(0) #<= # 0.23 keV) and a short pulse duration (Δt approx. = 3 to 4 ms) due to progressive degradation of the electron and ion temperatures. The second type (called Q-discharges) was obtained when the antenna was coated by TiN. These discharges were characterized by long pulse duration (Δt approx. = 50 ms), lower electron densities (ne(0) ≤ 4x1012cm-3) and higher temperatures (Ti ≤ 1.1 keV, Te ≤ 0.3 keV). The third type of discharge (called QR-discharges) was encountered when the magnetic configuration axis was shifted outwards by the transverse magnetic field. These discharges were characterized by relaxation oscillations of the plasma parameters, similar to those of the high-β S-regime of Heliotron E. (author)