EQUILIBRIUM IN HIGH BETA LOW MAGNETIC FIELD DISCHARGES OF URAGAN-2M

It has been shown that the plasma beta (β = nT/(μ0∙B2)) is relatively high in low magnetic field (BT ≈ 0.01 T) radio frequency discharges of the URAGAN-2M (U-2M) stellarator. This high beta is achieved in the low temperature (Tₑ = (10…50) eV) and density (nₑ = (0.5…1)∙10¹² cm-3) due to the very low magnetic field. In this work, we calculate the plasma equilibrium in these discharges using the VMEC code, with experimental density, temperature and plasma current values. The radio-frequency current drive can compensate the bootstrap current if the current directions are opposite, according to our calculations. This current drive can partially compensate U-2M equilibrium deterioration due to plasma beta effects. This effect may explain the experimentally observed dependence of the achieved plasma beta on the magnetic field direction in U-2M.