Model for the operation of an emissive cathode in a large magnetized-plasma

Abstract

A model for the steady-state operation of an emissive cathode is presented. The cathode, biased negative with respect to a cold anode, emits electrons thermionically and is embedded within a large magnetized-plasma column. The model provides formulas for the spatial shape of the global current system, the partition of potential across the plasma-sheath system, and the effective plasma resistance. The formation of a virtual cathode is explored, and an analytical expression for the critical operating conditions is derived. The model is further developed to include the self-consistent increase in plasma temperature which results from thermionic injection. In a companion paper [S. Jin et al., Phys. Plasmas 26, 022105 (2019)], results from transport experiments in the Large Plasma Device at the University of California Los Angeles are compared with this model, and excellent quantitative agreement is achieved.

Plasma flows generated by an annular thermionic cathode in a large magnetized plasma

“…An iterative procedure is used to calculate the spatial dependence of the plasma potential and plasma currents in terms of the externally applied bias and surface temperature of the emissive cathode-surface. This is done in two steps: first the potential is determined, 19 and second, this potential is used via a Braginskii transport code 25 to obtain the associated currents, resulting Ohmic heating term, and the electron temperature. The updated electron temperature and corresponding plasma conductivity feeds back into the calculation of the plasma potential.…”

“…A detailed description of the model used in this manuscript and additional supporting details are provided in a companion paper. 19 Here, only a brief summary of the important details is given. The model for the plasma potential is outlined in Sec.…”

“…This assumption of uniform plasma parameters, valid for the conditions considered here, allows the potential to be evaluated analytically. 19 Continuity of charge and quasi-neutrality yield an equation for the plasma potential…”

“…The experimental measurements are compared to predictions of a new model described in a separate, companion paper by Poulos. 19 The model calculates the spatial dependence of the plasma potential incorporating the boundary conditions associated with thermionic injection. The model is combined with a Braginskii transport code to calculate the electron temperature self-consistently.…”

Radial current and rotation profile tailoring in highly ionized linear plasma devices

“…Cross-field dynamics can turn out quite differently in plasmas with significant ion-neutral collisions, weak magnetization, or more complicated geometries. 7,19,20,24,[35][36][37][38][39][40] In the regime where this calculation does apply, it suggests some novel techniques with which the rotation profile might be controlled. Neutral beams, pellet injection, and electron injection can help shape the rotation profile by changing P and I.…”