We propose a novel scheme for monitoring the transition between deflagration and “detonation‐like” behavior of small‐scale explosive samples‐in‐vacuum subjected to short duration shock stimuli. Our approach relies on measuring the chemical identities and velocity distributions of the gaseous species produced by such samples; e.g. the relatively low velocity expansion‐quenched reaction intermediates produced by deflagration versus the hyperthermal thermodynamically stable molecules generated by the termination of a detonation wave at an explosive‐vacuum interface. We demonstrate our ability to detect such species by time‐of‐flight mass spectrometry (TOFMS) using fast Al atoms produced by laser ablation of aluminum metal. Extensive SIMION simulations of ion trajectories in our mass spectrometer lead to a semi‐quantitative model connecting the system operating parameters and the velocity‐dependent neutral species detection efficiency. We present a method for correcting our data for these detection biases, and for transforming them into neutral species velocity and kinetic energy distributions. We also present preliminary TOFMS data of hyperthermal organic molecular species produced by direct laser ablation/ignition of thin‐film nitrocellulose samples.
Using bismuth in place of gases such as xenon for Hall thruster propellant could potentially offer both physical and economical gains. As research continues to develop Hall thrusters that are fueled with bismuth, it will become advantageous to maintain one propellant supply rather than multiple supplies for the anode and cathode. The recent development of a bismuth Hall thruster at Michigan Tech, operated using a xenon LaB 6 cathode, provided a motive to explore the feasibility of developing an entire bismuth system. This paper provides a background on the development and operation of a bismuth vapor LaB 6 cathode. I. Introduction ISMUTH has many attributes that make it well suited for development as a Hall thruster propellant. Attractive physical characteristics follow from the atomic properties of bismuth. Bismuth, with an atomic mass of 209 amu, is significantly more massive than the more traditional xenon (131 amu). The large, heavy atoms thus have a lower neutral diffusion velocity and a larger electron-impact cross-section, resulting in a greater probability of ionization and increased propellant utilization. Not only is the ionization probability greater for Bi than Xe, but the energy cost-per-kg of mass flow to create a bismuth plasma is only 37% that of Xe: Bismuth's first ionization level is 7.3 eV, resulting in an ionization cost of 0.035 eV/amu, compared to xenon's
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