Measurement of the ion energy distribution resulting from the turbulent heating of a plasma

Measurements are reported of the ion energy spectrum of a turbulently-heated hydrogen plasma in the Cornell THM-2 experiment. The results show that the ion-heating mechanism simultaneously affects the entire length of the plasma column. Ion heating scales linearly with current, but the dependence on electric field strength is less than linear. The stored energy which drives the heating pulse is variable from 250 to 1000J. In all cases the ions account for approximately 10 percent of the total plasma energy. The efficiency of energy transfer to the plasma is approximately 4 percent, but for the most energetic condition the efficiency is found to be sensitive to the conductivity of the initially cold plasma. The H1+ energy spectrum sampled from the outer periphery of the plasma was measured during the first approximately 10 mu sec. During this time the energy spectrum is isotropic and well approximated by a two-temperature Maxwellian distribution. For the most energetic discharge the low energy component accounts for approximately 90 per cent of the ions and has Ti approximately=320 eV. The high energy component has Ti=1400 eV.