Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
Regular Articles
Abrupt Flushing of High-Density Core in Internal Diffusion Barrier Plasmas and its Suppression by Plasma Shape Control in LHD
Junichi MIYAZAWARyuichi SAKAMOTOSatoshi OHDACHIMasahiro KOBAYASHISuguru MASUZAKITomohiko MORISAKISatoru SAKAKIBARAMotoshi GOTOShigeru MORITAIchihiro YAMADAKazumichi NARIHARAHisamichi FUNABAKenji TANAKAClive A. MICHAELYasuhiro SUZUKIKiyomasa WATANABENobuyoshi OHYABUHiroshi YAMADAAkio KOMORIOsamu MOTOJIMAthe LHD experimental group
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2008 Volume 3 Pages S1047

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Abstract

Abrupt flushing of central density occurs in internal diffusion barrier (IDB) plasmas in the Large Helical Device (LHD), where a super dense core (SDC) of the order of 1020 m-3 is formed inside; this event is called “core density collapse (CDC).” CDC must be suppressed as further increase of the central pressure is inhibited. Since CDC is always accompanied by a large Shafranov shift of the plasma center, it has been supposed that mitigation of the Shafranov shift might affect CDC. Vertical elongation of the plasma shape (κ > 1) is effective in mitigating the Shafranov shift, and κ can be controlled with the quadrupole magnetic field BQ. To examine the impact of plasma shape control on CDC, BQ scan experiment has been performed in the LHD. The large Shafranov shift in IDB plasmas is mitigated by increasing κ. As a result, CDC is suppressed and high central β values of approximately 7% have been achieved in vertically elongated plasmas. The optimum κ varies with the magnetic configuration. Beta gradients greater than those at CDC in the κ = 1 configuration are observed without CDC in vertically elongated plasmas.

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© 2008 by The Japan Society of Plasma Science and Nuclear Fusion Research
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