Heating of a theta pinch at low electric field

Experimental and numerical results on plasma heating in a theta pinch at low azimuthal electric fields, Eθ ≲ 200 V · cm−1, are presented. Energy losses due to partial ionization of the initial plasma, and impurities, are shown to govern the final temperatures obtained. In particular, partial ionization results in a critical value of Eθ below which no effective heating occurs. This effect can be overcome by the use of negative bias fields, which increase the initial ionization and allow additional dissipative heating. At larger values of Eθ the initial heating rate is found to scale with