Vacuum Ultraviolet Absorption Measurements of Ground State Xenon in the Near Field of a Low Power Hall Thruster

Measurements are presented for the density of ground-state neutral xenon atoms in the near field of a 200W co-axial Hall thruster. The diagnostic strategy employed is a variation of a classical absorption technique, using retro-reflected intrinsic line emission from the resonance 147 nm vacuum ultraviolet (VUV) transition in atomic xenon as a source for absorption. In this way the technique has, in principal, the sensitivity of narrow-band absorption methods. Preliminary values for the near field number density (10 – 10m) are within range of those expected. The limitation in sensitivity and accuracy is due largely to a weak reflected emission beam, resulting primarily from losses in the optical components. Future experiments will make use of fully reflective optics, which provides easier alignment in the visible, and improved optical throughput in the 147 nm region studied.