Effects of lowering aspect ratio on magnetic fluctuations in RFP

• Main Authors: R. Ikezoe, T. Onchi, K. Murata, K. Oki, H. Shimazu, T. Yamashita, A. Sanpei, H. Himura, S. Masamune
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Magnetic Island; Single Island
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.575.7771; http://epsppd.epfl.ch/Hersonissos/pdf/P4_067.pdf

The reversed field pinch (RFP) is one of the magnetic confinement concept for compact high-beta plasmas. The quasi-single helicity (QSH) RFP state is a candidate for confinement improvement where the single dominant tearing mode grows significantly larger than the re-maining modes and the associated large magnetic island is immersed in otherwise stochastic core region[1, 2]. Within the large magnetic island of the dominant mode, favorable confine-ment has been realized. Recent equilibrium analysis have shown that by lowering the aspect ratio (A), mode rational surfaces are less densely spaced in the core region in the RFP. There-fore, the low-A RFP may expand the region to which the dominant single island can grow without interacting the neighboring islands and bring about simpler MHD dynamics. To explore the above-mentioned attractive low-A regime in RFP, we have been promoting a research program on RELAX (REversed field pinch of Low Aspect ratio eXperiment)[3]. RELAX is the low-A RFP machine, which has the world’s lowest aspect ratio of 2 (R = 0.5 m/a = 0.25 m) and uses 4-mm thick SS vacuum vessel with a field penetration time of ∼1.5 ms. It is operated without any other shell structure, and therefore, the vacuum vessel acts as a resistive shell.