Experimental and numerical characterization of ion-cyclotron heated protons on the Alcator C-Mod tokamak

Abstract

Energetic minority protons with -100 keV effective temperature are routinely created in Alcator C-Mod plasmas with the application of ICRF. A new multi-channel Compact Neutral Particle Analyzer is used to make measurements of these distributions in Alcator C-Mod's unique and reactor-relevant operating space via an active charge-exchange technique (CX). Using a detailed model that accounts for beam, halo, and impurity CX, core proton temperatures of 430-120 keV are directly measured for the first time in lower density (neo0 0.8 - 1.5 x 1020/m3) Alcator C-Mod plasmas using only 0.5 MW of ICRF power. The model found that the minority proton temperatures are peaked spatially away from r/a=O, even for an on-axis resonance. Additionally, noticeable phase-space anisotropy is seen as expected for ICRF heating. The measured effective temperatures scale approximately with the Stix parameter. The CNPA measurements are also compared with several leading simulation packages. Preliminary comparisons with results from the AORSA/CQL3D Full-wave/Fokker-Planck (FW/FP) code using a new synthetic diagnostic show good agreement and demonstrate that these complex codes are required to simulate Alcator C-Mod's energetic minority populations with accuracy. These FW/FP analyses represent the first comparison between predictions of such detailed codes and extensive minority ion experimental measurements.