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Evaluation of time evolution of 3-D Structure in Low-Aspect-Ratio RFP RELAX with SXR Imaging Technique

Author: Akio Sanpei
Requested Type: Poster Only
Submitted: 2014-05-30 08:57:27

Co-authors: S.Masamune, G.Ishii, R.Kodera, R.Ueba, Y.Aoki, H.Himura, S.Ohdachi, N.Mizuguchi, T.Akiyama

Contact Info:
Kyoto Institute of Technology
Goshokaido-cho, Matsugasaki, S
Kyoto, Kyoto   606-858
Japan

Abstract Text:
In a low-aspect-ratio (low-A) RFP machine RELAX (R = 0.51 m/a = 0.25 m (A = 2)), a quasi-periodic transition to quasi-single helicity (QSH) state has been observed. During the QSH state, the fluctuation power concentrates in the dominant m=1 mode, and a toroidally rotating three dimensional (3-D) helical structure has been observed with radial array of magnetic probes. We have applied a high-speed (10 micro sec time resolution) soft X-ray (SXR) imaging diagnostic system for the QSH studies in RELAX, with success to identify the characteristic helical SXR structures which suggest hot or dense helical core. The high-speed SXR imaging system has been extended to take the images from tangential and vertical directions simultaneously to deduce 3-D dynamic structures of the SXR emissivity.
The magnetic field topology for the QSH RFP phase in RELAX plasmas are calculated from obtained dual SXR images and results of external magnetic measurements. The calculated magnetic configuration suggests existence of a large magnetic island in shallow reversal discharge. Assuming rigid rotation, the Computed Tomography with Fourie-Bessel method from vertical SXR images also suggests that large magnetic island appears in QSH state in RELAX.
Recently, we have developed a two-dimensional electron temperature diagnostic system for thermal structure studies. The system consists of a SXR camera with two pin-holes for two-kinds of absorber foils, combined with a high-speed camera. We have succeeded in distinguishing Te image in QSH from that in multi-helicity (MH) RFP states.
The most recent results using above techniques will be presented, together with discussion on possible reconstruction methods from 3-D imaging.

Characterization: 1.2,3.0

Comments:
I will not be able to join the workshop on August 8.
If you could, please arrange my presentation on August 5-7.

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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