H{sub {alpha}} detector system for the Helically Symmetric Experiment

A system of absolutely calibrated H{sub {alpha}} detectors for neutral hydrogen monitoring has been designed and implemented for the Helically Symmetric eXperiment. An array of detectors at fixed poloidal angle but many toroidal angles yields a measurement of the toroidal asymmetry in H{sub {alpha}} emission and is used for monitoring hydrogen recycling. A multichord array at the toroidal angle of the gas puff allows an accurate determination of neutral gas penetration. Preliminary neutral gas modeling allows for the estimation of the density of atomic and molecular hydrogen from the H{sub {alpha}} emission, which are used for particle transport and flow damping studies.