Hollow cathode modeling: I. A coupled plasma thermal two-dimensional model

Abstract

A two dimensional axisymmetric quasi-neutral fluid model of an emissive hollow cathode that includes neutral xenon, single charge ions and electrons has been developed. The gas discharge is coupled with a thermal model of the cathode into a self-consistent generic model applicable to any hollow cathode design. An exhaustive description of the model assumptions and governing equations is given. Boundary conditions for both the gas discharge and thermal model are clearly specified as well. A new emissive sheath model that is valid for any emissive material and in both space charge and thermionic emission limited regimes is introduced. Then, setting the emitter temperature to an experimentally measured profile, we compare simulation results of the plasma model to measurements available in the literature for NASA NSTAR barium oxide cathode. Qualitative discrepancies between simulation results and measurements are noted in the cathode plume regarding the simulated plasma potential. Motivated by experimental evidence supporting the occurrence of ion acoustic instabilities in the cathode plume, an enhanced model of electron transport in the plume is presented and its consequences analyzed. Using the obtained plasma model, simulated quantities in the plume are qualitatively comparable with measurements. Inside the cathode, the simulated plasma density agrees well with measurements and is within the ±50 % experimental uncertainty associated with these measurements. A comparison of simulation results of the full coupled cathode model for the NASA NSTAR cathode with experimental measurements is presented in a companion paper, as well as a physical analysis of the cathode behavior and a parametric study of the influence of the operating point and key design choices.

Transition characteristics of low-pressure discharges in a hollow cathode

“…Although this approach is not as accurate as the hybrid model, the fluid model for hollow cathode discharges can be useful to provide qualitative trends in many cases. 18,[40][41][42][43][44] Also, the transient evolution of the discharge toward steady state can be very time consuming in the hybrid model, and the fully fluid model can be first used to approach the steady state. The present fluid model is less computationally expensive and can successfully predict the existence of the transition characteristics of discharges in a hollow cathode.…”

Propagation of ion acoustic wave energy in the plume of a high-current LaB6 hollow cathode

“…[12] In an effort to replace these simple closure models, more recent efforts have focused on finding first-principles relations for the IAT that self-consistently account for its propagation in an unsaturated state. [8,9,13] The evolution of the IAT predicted in these works, while showing promising initial results, has yet to be validated with direct experimental measurements. In light of these limitations of previous studies and the outstanding questions they invite about the correct hierarchy to describe the IAT, the need is thus apparent for a systematic, experimental study of its propagation in the cathode plume.…”

“…The need to reduce risk in the design and qualification of these systems for flight has driven the demand for increasingly high-fidelity predictive codes. But while the level of sophistication of models is improving, it has been recognized [8][9][10] that in * bjorns@umich.edu order to fully self-consistently model these devices, it is necessary to account for the propagation of the IAT in the plume.…”

Hybrid-PIC Simulation of LaB₆ Hollow Cathode Self-Heating Characteristics

“…Therefore, we used the above precedent values. As to modeling the anomalous resistivity in cathodes, more advanced models have been proposed such as the self-consistent model derived from kinetic theory, 20,21) but the conventional model is currently used for simplicity. With Eq.…”