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Measurements of Plasma Termination in ICRF Heated Long Pulse Discharges with Fast Framing Cameras in the Large Helical Device

Mamoru SHOJI, Hiroshi KASAHARA, Hirohiko TANAKA, Tetsuo SEKI, Kenji SAITO, Shuji KAMIO, Ryosuke SEKI, Takashi MUTOH, Masayuki TOKITANI, Shigeru MORITA, Motoshi GOTO, Tetsutaro OISHI, Eduardo DE LA CAL¹⁾, Carlos HIDALGO¹⁾, Hiroshi YAMADA 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 21 November 2014 / Accepted 5 March 2015 / Published 16 April 2015)

Abstract

The termination process of long pulse plasma discharges in the Large Helical Device (LHD) have been observed with fast framing cameras, which shows that the reason for the termination of the discharged has been changed with increased plasma heating power, improvements of plasma heating systems and change of the divertor configuration, etc. For long pulse discharges in FYs2010-2012, the main reason triggering the plasma termination was reduction of ICRF heating power with rise of iron ion emission due to electric breakdown in an ICRF antenna. In the experimental campaign in FY2013, the duration time of ICRF heated long pulse plasma discharges has been extended to about 48 minutes with a plasma heating power of ∼1.2 MW and a line-averaged electron density of ∼ 1.2 × 10¹⁹ m⁻³. The termination of the discharges was triggered by release of large amounts of carbon dusts from closed divertor regions, indicating that the control of dust formation in the divertor regions is indispensable for extending the duration time of long pulse discharges.

Copyright (c) 2015 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

long pulse discharge, ICRF heating, dust, closed divertor, LHD

DOI: 10.1585/pfr.10.3402040

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This paper may be cited as follows:

Mamoru SHOJI, Hiroshi KASAHARA, Hirohiko TANAKA, Tetsuo SEKI, Kenji SAITO, Shuji KAMIO, Ryosuke SEKI, Takashi MUTOH, Masayuki TOKITANI, Shigeru MORITA, Motoshi GOTO, Tetsutaro OISHI, Eduardo DE LA CAL, Carlos HIDALGO, Hiroshi YAMADA and the LHD Experiment Group, Plasma Fusion Res. 10, 3402040 (2015).