Spectroscopic Measurement of Bismuth for Optical Diagnostics

Abstract

Bismuth has received considerable attention recently as a propellant option for more advanced, next-generation Hall thrusters. A bismuth-fueled Hall thruster would possess advantages over conventional xenon thrusters in terms of efficiency, power-handling, and simplicity of ground testing facilities. In developing such a thruster, there is a need for nonintrusive diagnostic methods for taking the necessary measurements to optimize the geometry and operating conditions. A previous paper discussed such optical diagnostic methods for analyzing the velocity, energy, and number densities of BiI and BiII in the plume. Additionally, candidate transitions for measurement were selected and their lineshapes modeled in terms of hyperfine splitting and broadening mechanisms. In this paper, after a brief summary of the previous work, the line selections will be revised for improved accessibility to commercial tunable diode lasers. A lineshape model that more closely relates to Hall thruster measurements will also be discussed. Finally, the development of laboratory systems for taking measurements on a Bi gas will be discussed, and measurements of the Bi spectrum will be presented.

On the level system of Bi II

“…These data are of interest not only for astrophysical investigations, but also for technical applications, as e.g. diagnosis for Hall-thrusters [20][21][22].…”

Measurements in Stationary Reference Bi Discharge Cell for Diagnostics of a Bismuth Hall Thruster

“…In order to measure these quantities via non-intrusive optical diagnostics, it is necessary first to select electronic transitions for measurement, and to analyze the structure of each transition so that data can be properly interpreted. The general spectroscopy necessary to begin this analysis for bismuth has been discussed in previous conference proceedings, 5,6,7 and will not be repeated here.…”

“…Previously, 5,6,7 several candidate Bi transitions were selected for analysis and discussed. The transition selected for ground state Bi I number density determination by atomic resonance absorption spectroscopy was the line at vacuum wavelength 306.86nm (6p The selection of the 680.9 nm transition provides several advantages.…”