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Direct Measurement of Reconnection Outflow Profile by Glass-Tube-Pair Type Doppler Probes in Tokamak Merging Experiments

Ryo SOMEYA, Luo JIAXIAO, Yunhan CAI, Tara AHMADI, Hiroshi TANABE, Yasushi ONO

Graduate School of Frontier Sciences, The University of Tokyo, Tokyo 113-0032, Japan

(Received 21 April 2025 / Accepted 20 June 2025 / Published 16 September 2025)

Abstract

The reconnection outflow velocity under high guide field was directly measured using the 1D array of ion Doppler probes and was compared with the E × B, gradient B, and curvature drift velocity calculated from 2D profile measurements of electric and magnetic fields for the first time. It was found that the measured ion velocity profile agrees well with the profile of E × B drift velocity which is much larger than the other drift velocities. The poloidal flux-line velocity is almost equal to the E × B drift and ion flow velocities, probably because magnetic flux is almost frozen into ions due to its large Lundquist number of 10².

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

merging tokamaks, magnetic reconnection, ion outflow, Doppler spectroscopy, ion drift velocity

DOI: 10.1585/pfr.20.1402041

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