Computation of Neutral Gas Flow From a Hall Thruster Into a Vacuum Chamber

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. Abstract. The finite pressure present in vacuum chamber testing of space propulsion systems such as Hall thrusters can have a number of undesirable effects. For example, the thrust generated by the thruster is higher and the plume divergence angle larger in ground tests in comparison to space operation. To try to quantify these effects, the direct simulation Monte Carlo method is applied to model a cold flow of xenon gas expanding from a Hall thruster into a vacuum chamber. The simulations are performed for the P5 Hall thruster operating in a large vacuum tank at the University of Michigan. Comparison of the simulation results is made with experimental measurements of pressure obtained with a series of ion gauges. The mass flow rate through the thruster and the total pumping speed of the vacuum chamber are varied. A key physical parameter in the simulations concerns the probability that a xenon atom incident on a cryogenic pumping panel actually sticks to the panel. For a reasonable range of values for the sticking coefficient, excellent agreement between simulation and experiment is obtained for several different conditions. REPORT DATE (DD-MM-YYYY) REPORT TYPE Technical Papers DATES COVERED

A kinetic Fokker–Planck approach to model hard-sphere gas mixtures

“…The evolution of distribution functions is described by kinetic models, such as the set of Boltzmann equations (1). Of particular interest is the behavior of kinetic models in the continuum limit.…”

“…Many applications of aerodynamics, for example, the modeling of gas flows in vacuum systems 1 or reentry flows, 2 require the modeling of a wide range of rarefaction and nonequilibrium effects. The magnitude of non-equilibrium is often characterized by the Knudsen number Kn = λ/l, where λ denotes the particle mean free path and l is a characteristic length scale of the regarded problem.…”

“…Hence, the modeling of gas mixtures is an essential task for the treatment of a number of aerodynamic problems such as reentry flows, 2 expansion flows, 3 or flows in vacuum facilities. 1 In continuum theory, the treatment of mixtures is usually simplified by several assumptions, such as the postulation of an equalized temperature for all particle species. 4 However, in strong non-equilibrium flows, these simplifications lose their validity.…”

Propellant Flow Analysis within Electric Propulsion Test Facility

“…As described in this paper, the analytical thruster parameters are determined by referring to the general hall-effect thruster and the 600 mN Hall-effect thruster (HET), which is expected to be developed in Japan in the near future. [1][2][3][4][5][6][7]13,14) Table 1 presents the specifications. For generalization of the results, the propellant is assumed to be uniformly diffuse with its thermal velocity with the diffusion angle.…”

“…Because the propellant around the thruster, especially the near downstream region, affects the plasma generation and acceleration, thruster performance and durability differ between that in the ground test and in the space operation. [1][2][3][4][5][6][7] This difference produces an estimation error. It is conceivable that an unnecessary increase in weight (e.g., overloading of a propellant or increase in the weight of a power supply system) or a mission failure can occur in a shorter time than the period assumed for durability.…”