Plasma and Fusion Research

Volume 15, 2402009 (2020)

Regular Articles

Langmuir Probe Measurements of Scrape-Off Layer Conditions in RF-Driven Plasmas in TST-2
James H.P. RICE, Naoto TSUJII, Yuichi TAKASE, Akira EJIRI, Osamu WATANABE, Hibiki YAMAZAKI, Yi PENG, Kotaro IWASAKI, Yuki AOI, Yongtae KO, Kyohei MATSUZAKI and Yuki OSAWA
The University of Tokyo, Kashiwa 277-8561, Japan
(Received 28 November 2019 / Accepted 20 February 2020 / Published 6 April 2020)

Abstract

A new Langmuir probe has been designed and installed in TST-2 for measurements of Scrape-Off Layer plasmas (SOL). Non-inductive current drive is considered essential for spherical tokamak reactors. It has previously been shown that a large amount of injected Lower Hybrid Wave (LHW) power is lost in the SOL [1]. A full density profile of SOL conditions is necessary to accurately simulate the propagation of LHW in TST-2. A new probe was designed for durability, larger signal and Mach probe measurements. The new probe has been installed in TST-2 and results have been obtained. Temperature measurements show Te = 30 - 50 eV during RF injection and < 10 eV otherwise. Density measurements show ne = 2.0 × 1015 m−3 and 1.5 × 1016 m−3 during flat-top RF power injection from Outboard- and Top-launch antennas, respectively. This is above the cut-off density for the 200 MHz LHW (5 × 1014 m−3) in TST-2, thus LHW can propagate through SOL plasma.

Keywords

Langmuir probe, Mach probe, lower-hybrid wave, spherical tokamak

DOI: 10.1585/pfr.15.2402009

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Publisher's Note

This article has an erratum: James H.P. RICE et al., Plasma Fusion Res. 15, 2902058 (2020).