Development of high-frequency magnetic probe for plasma diagnostics of XuanLong-50

TL;DR

This paper reports the design and testing of a high-frequency magnetic probe for plasma diagnostics on the XuanLong-50 spherical torus, capable of detecting high-frequency magnetic fluctuations and instabilities.

Contribution

A novel high-frequency magnetic probe was developed and validated for plasma diagnostics, enabling detection of high-frequency fluctuations and instabilities in spherical torus plasmas.

Findings

Probe operates within 1-180 MHz frequency range.

Detected high-frequency instabilities and frequency chirping.

Results align with Berk-Breizman bump on tail instability model.

Abstract

A high-frequency magnetic probe has been designed and developed on XuanLong-50 (EXL-50) spherical torus to measure high-frequency magnetic field fluctuations caused by energetic ions and electrons in the plasma. The magnetic loop, radio filters, radio-frequency (RF) limiter, and data acquisition system of the probe are described in detail. The results of the preliminary test show that the probe can have a frequency response within the 1- 180 MHz range. The fluctuation data from the EXL-50 plasma were analyzed in the time-frequency domain using fast Fourier transforms. Using this diagnostic system, distinct high-frequency instabilities were detected. In particular, significant frequency chirping was observed, which is consistent with the bump on tail drive instability predicted by the Berk-Breizman model.