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Observation of Termination Process of Long Pulse Plasma Discharges Using Stereoscopic Fast Framing Cameras in the Large Helical Device

Mamoru SHOJI, Hiroshi KASAHARA, Hirohiko TANAKA, Takanori MURASE, Masahiko TOKITANI, Shigeru MORITA, Motoshi GOTO, Tetsutaro OISHI, Takashi MUTOH, Eduardo DE LA CAL¹⁾, Calros HIDALGO¹⁾ and the LHD Experiment Group

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan

1)

Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 40 Avenida Complutense, Madrid 28040, Spain

(Received 23 November 2015 / Accepted 11 March 2016 / Published 15 April 2016)

Abstract

Long pulse discharges in the Large Helical Device (LHD) were interrupted by the emission of large amounts of carbon dusts released from a closed helical divertor in the previous experimental campaign (FY2013). In order to control the dust emission, the configuration of the closed divertor near lower and upper ports was modified in the last experimental campaign (FY2014). While the modification of the divertor configuration has successfully controlled the release of dusts, long pulse discharges were often terminated with abrupt increase in iron ion emission. The termination process of a long pulse plasma discharge was observed with a stereoscopic fast framing camera which can identify the three-dimensional positions of dusts. It proved that the dusts penetrated into the main plasma through the plasma periphery, which could induce the radiation collapse in the plasma discharge.

Copyright (c) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

long pulse discharge, stereoscopic observation, dust, fast framing camera, LHD

DOI: 10.1585/pfr.11.2402056

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