Global Confinement, Sawtooth Mixing, and Stochastic Diffusion Ripple Loss of Fast ICRF-driven H+ Minority Ions in TFTR

Abstract

This paper presents studies of ICRF-driven H + minority ions in TFTR deuterium plasmas using primarily passive H o flux detection in the energy range of 0.2-1.0 MeV with some corroborating active (Li pellet charge exchange) measurements. It is shown that in the passive mode the main donors for the neutralization of H + ions in this energy range are C 5+ ions. The measured effective H + tail temperatures range from 0.15 MeV at an ICRF power of 2 MW to 0.35 MeV at 6 MW. Analysis of the ICRF-driven H + ion energy balance has been performed on the basis of the dependence of effective H + temperatures on the plasma parameters. The analysis showed that H + confinement times are comparable with their slowing down times and tended to decrease with increasing ICRF power. Radial redistribution of ICRF-driven H + ions was detected when giant sawtooth crashes occurred during the ICRF heating. The redistribution affected ions with energy below 0.7-0.8 MeV. The sawtooth crashes displace H + ions outward along the plasma major radius into the stochastic ripple diffusion domain were those ions are lost in ~ 10 milliseconds. These observations are consistent with the model of the redistribution of energetic particles developed previously to explain the results of DT alpha particle redistribution due to sawteeth observed in TFTR. The experimental data are also consistent with ORBIT code simulations of H + stochastic ripple diffusion losses.