Sensitivity of MSE measurements on the beam atomic level population

The effect of variation in atomic level population of a neutral beam on the Motional Stark Effect (MSE) measurements is investigated in the low density plasmas of HSX stellarator. A 30 KeV, 4 A, 3 ms hydrogen diagnostic neutral beam is injected into HSX plasmas of line averaged electron density ranging from 2 to 4 . 10(18) m(-3) at a magnetic field of 1 T. For this density range, the excited level population of the hydrogen neutral beam is expected to undergo variations. Doppler shifted and Stark split H-alpha and H-beta emissions from the beam are simultaneously measured using two cross-calibrated spectrometers. The emission spectrum is simulated and fit to the experimental measurements and the deviation from a statistically populated beam is investigated. Published by AIP Publishing.