Stirring Unmagnetized Plasma

TL;DR

This paper demonstrates a novel method to induce rotation in unmagnetized plasma by using magnetized edges and biased cathodes, showing viscous coupling and solid-body rotation in experiments.

Contribution

It introduces an experimental technique for spinning unmagnetized plasma via edge-driven currents and torque, highlighting viscous coupling effects.

Findings

Core plasma rotates as a solid body

Viscous coupling transfers momentum from edge to core

Collisional viscosity overcomes ion-neutral drag

Abstract

A new concept for spinning unmagnetized plasma is demonstrated experimentally. Plasma is confined by an axisymmetric multi-cusp magnetic field and biased cathodes are used to drive currents and impart a torque in the magnetized edge. Measurements show that flow viscously couples momentum from the magnetized edge (where the plasma viscosity is small) into the unmagnetized core (where the viscosity is large) and that the core rotates as a solid body. To be effective, collisional viscosity must overcome the ion-neutral drag due to charge exchange collisions.