Krypton tagging velocimetry in the plume of a plasma hollow cathode

Abstract

Krypton tagging velocimetry (KTV) is an emerging flow diagnostic that investigates the bulk movement of high-speed, low-pressure gas flows. The present contribution expands the typical KTV method to the lower density (vacuum) conditions of interest in electric propulsion research. Our KTV scheme utilizes a two-photon (Write) excitation at 214.7 nm from a pulsed dye laser, followed by (Read) re-excitation of the ensuing metastable at 769.5 nm with an optical parametric oscillator. For the case of cold krypton gas expanding from a hollow cathode into vacuum, we find a bulk velocity of 452 ± 37 m/s and temperature of 20 ± 16 K. We also study the flow in the plume with the hollow cathode plasma operating for which we find bulk velocity of 1200 ± 130 m/s and temperature of 880 ± 370 K. Measurements are performed at background pressures down to ∼10−5 Torr.