LASER-INDUCED FLUORESCENCE STUDY OF A XENON HALL THRUSTER

Laser-induced fluorescence of the neutral-xenon 6s[3/2](2)(0) --> 6p[3 /2](2)(P-3(2) -- D-1(2)) transition at 823.2 nm and the xenon-ion 5d[3 ](7/2) --> 6p[2](5/2)(0) (D-4(7/2) -- P-4(5/2)) transition is used to measure plasma parameters in the plume of a laboratory-model xenon Hal l thruster. The Hall discharge operates nominally at 62 V, 4.2 A, and 3.2 mgs(-1) xenon flow with an overall thruster power of 320W. A tunab le semiconductor diode laser and an Ar+-pumped dye laser are used to p robe the respective excited-state transitions. Axial velocity measurem ents are made at a number of axial and radial locations up to 4.5 cm d ownstream of the thruster-exit plane and under a variety of thruster o perating conditions. Neutral velocities from 100 ms(-1) to 400 ms(-1) and ion velocities as high as 12 kms(-1) are calculated from measured Doppler shifts. The charge-exchange phenomenon evidently does not sign ificantly affect the xenon neutrals. The spectralline shapes of the io n indicate a spread in ion energies through a non-Maxwellian distribut ion of axial velocities. Neutral kinetic temperatures of 500(+/-200)K are observed under standard operating conditions. Zeeman and Stark eff ects on the spectral-line shapes, from the thruster's magnetic and ele ctric fields, are not substantial. The measured line center of the ion transition is 16521.23 (+/-0.02) cm(-1).