Design of a time-resolved laser-induced fluorescence diagnostic for measuring Kr-ion flows in novel thruster configurations

A laser-induced fluorescence diagnostic intended to measure time-resolved Kr-ion flow vectors in Hall thruster and inductive pulsed plasma thruster discharges is described. The design relies on a 'sample-hold' technique which employs a gated integrator to measure the integrated fluorescent light emission within a user-specified window relative to a given discharge's time-varying current while the pump wavelength is swept over a timescale encompassing several discharge cycles. The measurement is repeated once every discharge cycle within the user-specified window until the pump wavelength's scan is completed. In this way, an ion velocity distribution function (IVDF) of Kr ions can be measured to determine their flow either via fits to a Maxwellian or by taking the IVDF's first moment. 'Toy model' examples of the sample-hold technique and its use with a lock-in amplifier are provided alongside initial measurements from a Hall thruster discharge.