Trapped Particle Stability for the Kinetic Stabilizer

TL;DR

This paper investigates the stability conditions of a kinetically stabilized tandem mirror, focusing on MHD stability and trapped particle modes, revealing challenges in power constraints and electron connection requirements.

Contribution

It provides a detailed analysis of the stability criteria for the kinetic stabilizer in tandem mirrors, highlighting the constraints posed by trapped particle modes and power drain issues.

Findings

Trapped particle mode stability is more restrictive than MHD stability.

Achieving stability requires careful electron connection management.

Power drain from electron connection poses significant challenges.

Abstract

A kinetically stabilized axially symmetric tandem mirror (KSTM) uses the momentum flux of low-energy, unconfined particles that sample only the outer end-regions of the mirror plugs, where large favorable field-line curvature exists. The window of operation is determined for achieving MHD stability with tolerable energy drain from the kinetic stabilizer. Then MHD stable systems are analyzed for stability of the trapped particle mode. This mode is characterized by the detachment of the central-cell plasma from the kinetic stabilizer region without inducing field-line bending. Stability of the trapped particle mode is sensitive to the electron connection between the stabilizer and the end plug. It is found that the stability condition for the trapped particle mode is more constraining than the stability condition for the MHD mode, and it is challenging to satisfy the required power constraint. Furthermore a severe power drain may arise from the necessary connection of low-energy electrons in the kinetic stabilizer to the central region.