A Method for Propellant-Agnostic Laser Induced Fluorescence for Hall Thrusters

As prices of Xenon have increased and remained uncertain, many have considered changing to other propellants such as Krypton and Argon. Doing so provides challenges given that thrusters operate quite differently on these other propellants, due to the differences in ionization and instabilities in the plasma. This necessitates more investigation into the plasmas itself, however this can be a further challenge as much of the diagnostic architecture has been built to probe Xenon. This is particularly evident in laser induced fluorescence (LIF), which requires lasers and controllers for the specific wavelength of Xenon excitation. To perform LIF on Krypton plasmas would require purchasing a new laser and support equipment, which is both expensive and can take months to attain. An alternate method to use existing Xenon LIF setups to probe non-Xenon plasmas has been demonstrated at JPL on a Hall thruster operating on Krypton, which would enable rapid testing of propellants without changing the diagnostic setup. This is achieved by leaking miniscule amounts of Xenon through the thruster to serve as tracers. Experimental results of this method are shown, with results discussing how xenon flow fraction affects both signal to noise ratio of the LIF signal and the Krypton plasma.