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

Abstract

A LaB 6 thermionic emitter of annular shape is used in the Large Plasma Device at the University of California, Los Angeles to create off-axis heating conditions for various transport studies. Since the emitter is biased relative to a distant anode, which is many collision lengths away, the entire magnetized plasma develops a self-consistent, potential structure that simultaneously generates transverse and axial flows with shear. This study uses swept Langmuir probe techniques and Mach probes to map the flow patterns and their dependence on bias and plasma parameters. By implementing additional biasing configurations, it is possible to control the magnitude of the flows and their shear strength. The experimental measurements, including the selfconsistent currents, are compared to predictions of a model that incorporates the boundary conditions associated with thermionic injection, combined with a Braginskii transport code for the electron temperature.

A necessary condition for perpendicular electric field control in magnetized plasmas

“…To avoid further complications, we focus here on end-electrodes biasing experiments in linear geometry. In addition, and despite the promising results shown by emissive electrodes for electric field and rotation control 45,52 , we further restrict our study to non-emissive electrodes, and consider a set of experiments surveyed in a previous study 21 . These experiments range from low density, low temperature plasmas used in the study of basic plasma phenomena 53,54 to high density, high temperature plasmas produced in magnetic confinement fusion devices 55,56 and thus offer the opportunity to test theoretical models across a wide range of plasma parameters.…”

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

“…Detailed results from transport experiments 18 conducted in the Large Plasma Device (LAPD) 19 at the University of California, Los Angeles (UCLA) and comparisons to the model are presented in a companion paper. 20 It is found that the model exhibits excellent quantitative agreement with the electron physics in the experiments; however, there are subtleties in the fieldaligned ion-flow which remain elusive.…”

“…Section V offers an extension of the model for a ring-shaped cathode, which corresponds to the configuration used in Ref. 20. Section VI further expands the model to include the selfconsistent calculation of the increase in plasma-temperature.…”

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.…”

“…Substitution of these variables into the continuity Eq. (19) and charge conservation Eq. (20), using the velocity in Eq.…”