Characterization of the SCR-1 Stellarator Physics: Investigating Plasma Discharge, MHD Equilibrium Calculations, and O-X-B Mode Conversion Feasibility

TL;DR

This study characterizes the SCR-1 stellarator's plasma behavior, magnetic equilibrium, and wave conversion feasibility, providing insights into plasma stability, heating mechanisms, and wave interactions in a low aspect ratio device.

Contribution

It offers new analysis of plasma profiles, magnetic flux surfaces, and wave conversion processes in SCR-1, including stability criteria and wave heating feasibility assessments.

Findings

Maximum O-X conversion efficiency reached 63% with reflection effects.

Magnetic well contributes to plasma stability in SCR-1.

Steep density gradients significantly affect wave conversion processes.

Abstract

The Stellarator de Costa Rica 1 (SCR-1) is a modular stellarator with a small aspect ratio that serves as a valuable research and training tool for plasma magnetic confinement. This study explored a new heating mechanism and the factors that influence it. The current state of the device and plasma discharge are initially presented. Subsequently, the measurement process was utilized to determine radial profiles of electron density and electron temperature using a single Langmuir probe, and the results were compared with theoretical predictions based on the particle and energy balance. Additionally, the VMEC code was employed to calculate magnetic flux surfaces with characteristics such as a low aspect ratio, low beta parameter, negative magnetic shear, and decreasing rotational transform along magnetic flux surfaces. The Mercier criterion was employed to conduct a linear stability analysis, which identified a magnetic well that played a crucial role in the linear stability of the majority of magnetic flux surfaces. Feasibility studies of electron Bernstein waves were conducted using the IPF-FMDC full-wave code, with input files generated from the device and known plasma characteristics. The results obtained from the IPF-FMDC full-wave code revealed that the O-X conversion percentage reached a maximum of 63 % when considering radiation reflection in the vacuum vessel. Significant effects of plasma curvature on the O-X wave conversion and normalized electron density scale length were observed, while the change in the SCR-1 heating position did not produce a significant impact. Three damping mechanisms affecting O-X conversion were studied, and one of the principal effects was the SX-FX conversion due to steep electron density gradient. Additionally, stochastic electron heating showed a low electron field amplitude, which is important for limiting the electron Bernstein wave propagation.