Non-inductive plasma current sustainment with stochastic electron cyclotron in EXL-50 spherical torus

TL;DR

This paper demonstrates for the first time the start-up and sustainment of plasma current in a spherical torus using only electron cyclotron waves, showing insensitivity to injection angle and a linear relation with X-ray spectrum slope.

Contribution

It introduces a novel method of plasma current sustainment via stochastic electron cyclotron waves in a spherical torus, validated through experimental results.

Findings

Plasma current is insensitive to ECW injection angle.

Current correlates linearly with X-ray spectrum slope.

Maximum plasma current achieved is 150 kA with 140 kW ECW.

Abstract

The start-up and sustainment of a stochastic wave non-inductive current on a spherical torus was experimentally demonstrated for the first time using only electron cyclotron waves. The plasma current is insensitive to the injection angle of ECWs and approximately linearly correlated with the slope of the X-ray spectrum. Its direction is determined by the vertical magnetic field (BV). The temporal development in the number of X-ray bremsstrahlung photons with a specified energy is consistent with the stochastic heating model. Moreover, the ratio of Amps to Watts of the ECW is generally >1 kA/kW under normal conditions (maximum plasma current: 150 kA, ECW: 140 kW). The experimental results are explained using the stochastic heating model of the asymmetric electron velocity distribution in stochastic electromagnetic waves.