Observation of helical structure by imaging diagnostics in a low-aspect-ratio reversed field pinch

Takumi Onchi, Ryuya Ikezoe, Kensuke Oki, Akio Sanpei, Haruhiko Himura, Sadao Masamune, Nobuhiro Nishino, Haruhisa Koguchi

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Abstract

Study of helical structure has been in progress in shallow reversal reversed field pinch (RFP) plasmas in a lowaspect- ratio machine RELAX (R=a = 0:5 m/0.25 m, A = 2) by using visible light and soft-X-ray (SXR) imaging diagnostics. Simple helix and its toroidal rotation have been observed in tangential visible light images taken by a highspeed camera. Similar simple filament structures have also been observed in tangential images obtained by a pin-hole SXR camera assembled with Image-intensified charged coupled device (ICCD). The SXR experimental images have been compared with calculated tangential images using model profiles for emissivity to identify the plausible SXR emissivity profile. It has been found that a model profile of helical core having SXR emissivity 2-4 times higher than the background provides 2D SXR images in reasonable agreement with the experimental results. Time evolution of the SXR emissivity profile measured with a photodiode array has shown that the emissivity is the highest in the core region with a quasi-periodic oscillation of the peak position.

Original languageEnglish
Article number114501
JournalJournal of the Physical Society of Japan
Volume80
Issue number11
DOIs
Publication statusPublished - Nov 2011
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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