Electron-cyclotron plasma startup in the GDT experiment

TL;DR

This paper introduces a novel plasma startup method in the GDT device using electron cyclotron resonance to generate seed plasma, enabling efficient neutral beam injection without traditional plasma sources.

Contribution

It presents the first experimental demonstration and theoretical modeling of ECR-based seed plasma generation in a large-scale magnetic mirror device.

Findings

ECR heating successfully ionizes neutral gas to form seed plasma.

The seed plasma evolution depends on microwave power, magnetic configuration, and gas pressure.

The new startup scenario produces comparable plasma conditions to conventional methods.

Abstract

The paper reports on a new plasma startup scenario in the Gas Dynamic Trap (GDT) magnetic mirror device. The primary 5 MW neutral beam injection (NBI) plasma heating system fires into a sufficiently dense plasma target ("seed plasma"), which is commonly supplied by an arc plasma generator. In the reported experiments, a different approach to seed plasma generation is explored. One of the channels of the electron cyclotron resonance (ECR) heating system is used to ionize the neutral gas and build up the density of plasma to a level suitable for NBI capture. After a short transition (about 1 ms) the discharge becomes essentially similar to a standard one initiated by the plasma gun. The paper presents the discharge scenario and experimental data on the seed plasma evolution during ECR heating, along with the dependencies on incident microwave power, magnetic configuration and pressure of a neutral gas. The characteristics of consequent high-power NBI discharge are studied and differences to the conventional scenario are discussed. A theoretical model describing the ECR breakdown and the seed plasma accumulation in a large scale mirror trap is developed on the basis of the GDT experiment.