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Measurement of the Local Current Density Inside a Current Sheet Using a Rogowski Coil Array on UTST Merging Plasmas

Hibiki YAMAZAKI, Hirokazu FURUI, Kotaro YAMASAKI¹⁾, Tomohiko USHIKI, Akira EJIRI, Michiaki INOMOTO, Yuichi TAKASE, Yasushi ONO, Naoto TSUJII, UTST group and TST-2 group

The University of Tokyo, Kashiwa 277-8561, Japan

1)

Kyushu University, Fukuoka 819-0395, Japan

(Received 9 April 2018 / Accepted 5 June 2018 / Published 26 July 2018)

Abstract

Plasma merging is a unique method of plasma start-up, and magnetic reconnection is a key process for plasma heating in this method. On the University of Tokyo Spherical Tokamak (UTST), we use a pickup coil array to obtain the macroscopic behavior of magnetic reconnection, but direct measurement of the localized current is still necessary to study the details of the magnetic reconnection process. A small Rogowski coil is a useful tool for measuring small scale currents, and we used five such coils to measure the radial structure near the X-points of merging plasmas on UTST. As a result, we have found current densities up to 1.5 MA/m², with a typical time scale of several micro seconds. The current density increases with the plasma current, and the average radial width is about 30 mm.

Copyright (c) 2018 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

spherical tokamak, start-up, plasma merging, magnetic reconnection, Rogowski coil

DOI: 10.1585/pfr.13.1202093

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