Measurements of Fast Ion Distribution in ICRF Heated Plasmas

Alcator C-Mod uses ICRF for the bulk auxiliary heating and relies primarily on hydrogen minority heating scenarios. Measuring the resulting hydrogen ion distribution provides an opportunity to validate ICRF upgraded simulation capability that includes non-Maxwellian ions. The Compact Neutral Particle Analyzer (CNPA) is a diagnostic employed on Alcator C-Mod to measure this fast ion distribution function. The diagnostic consists of silicon diode detectors that have a direct view of the plasma from the top of the vessel. Hydrogen particles neutralize, exit the plasma and impinge on the detector producing pulses proportional to their energy. Analysis of the pulse height distribution can provide the energy distribution of the fast ion tail, serving as a benchmark for simulation results and allowing for an assessment of the simulation algorithm and physics kernel. In this poster, we will present results from the detector in the most recent campaigns. We will also describe the calibration of the detector and lastly we will provide plans for expanding the detector in the upcoming campaign.