Installation and Commissioning of an Ion Temperature Diagnostic for Transport Studies on the Pegasus-III Spherical Tokamak

Pegasus-III is an ultra-low aspect ratio spherical tokamak focused on non-solenoidal startup techniques. Edge ion temperatures of non-solenoidal plasmas on Pegasus were measured via impurity ion measurements to be about 10 times larger than the electron species due to reconnection heating. This mechanism depends on charge and mass; thus, a compact neutral particle analyzer (CNPA) has been chosen for use on Pegasus-III due to its sensitivity to the majority ion temperature. This CNPA is a 25 channel E parallel to B analyzer with a helium stripping cell designed to resolve Maxwellian majority ion temperatures or non-Maxwellian features in the ion temperature distribution at a 20 kHz sampling frequency. For Pegasus-III installation, the CNPA is placed radially with an integrated line of sight allowing for toroidal averaging. Particles are detected based on their energy via channel electron multipliers. For Pegasus-III, only the majority ion species of deuterium is analyzed. This CNPA is calibrated to recover majority ion temperatures in the range of 0.1–2 keV sufficient for analysis of ions in the Pegasus-III experiment.