Measurement of Wave Electric Fields in Plasmas by Electro-Optic Probe

TL;DR

This paper demonstrates a high-frequency electro-optic sensor for measuring wave electric fields in plasma environments, enabling precise comparison between experimental data and simulations, and revealing field enhancements in inhomogeneous plasmas.

Contribution

The study introduces a novel electro-optic sensor system for plasma electric field measurement that effectively separates electrostatic waves from magnetic fields and is suitable for in situ plasma diagnostics.

Findings

Measured wave electric fields agree with simulations in air.

Electric fields are enhanced in inhomogeneous plasma regions.

Potential antenna oscillations may explain field discrepancies.

Abstract

Electric field measurement in plasmas permits quantitative comparison between the experiment and the simulation in this study. An electro-optic (EO) sensor based on Pockels effect is demonstrated to measure wave electric fields in the laboratory magnetosphere of the RT-1 device with high frequency heating sources. This system gives the merits that electric field measurements can detect electrostatic waves separated clearly from wave magnetic fields, and that the sensor head is separated electrically from strong stray fields in circumference. The electromagnetic waves are excited at the double loop antenna for ion heating in electron cyclotron heated plasmas. In the air, the measured wave electric fields are in good absolute agreement with those predicted by the TASK/WF2 code. In inhomogeneous plasmas, the wave electric fields in the peripheral region are enhanced compared with the simulated electric fields. The potential oscillation of the antenna is one of the possible reason to explain the experimental results qualitatively.