Abrupt Flushing of High-Density Core in Internal Diffusion Barrier Plasmas and its Suppression by Plasma Shape Control in LHD

Junichi MIYAZAWA, Ryuichi SAKAMOTO, Satoshi OHDACHI, Masahiro KOBAYASHI, Suguru MASUZAKI, Tomohiko MORISAKI, Satoru SAKAKIBARA, Motoshi GOTO, Shigeru MORITA, Ichihiro YAMADA, Kazumichi NARIHARA, Hisamichi FUNABA (+9 others)
2008 Plasma and Fusion Research  
Received day month year / Accepted day month year should be centered 10-point type) A super-dense core of the order of 10 20 m -3 is formed inside the internal diffusion barrier (IDB) during the reheat phase of the central pressure after pellet injection in LHD. Large Shafranov shift of the plasma center is observed in IDB plasmas and it reaches roughly 50 % of the plasma minor radius. In some cases, abrupt flushing of the central density takes place and this event is called as "core density
more » ... lapse (CDC)". CDC must be suppressed since it inhibits further increase of the central pressure. CDC is always accompanied by large Shafranov shift of the plasma center exceeding a critical position. Theoretically, it is predicted that vertical elongation of the plasma shape (κ > 1) is effective to mitigate the Shafranov shift and the κ is controllable with the quadrupole magnetic field, B Q . According to this prediction, B Q scan experiment has been performed in LHD. Shafranov shift is indeed mitigated by increasing κ. As a result, CDC is suppressed and high central β values reaching ~ 7 % have been achieved in vertically elongated plasmas.
doi:10.1585/pfr.3.s1047 fatcat:swgwmhj5czhhdotis3kjucovoe