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High Power Reconnection Heating of FRCs and STs in TS-3 and TS-4 Merging Experiments

Author: Yasushi Ono
Requested Type: Consider for Invited
Submitted: 2011-06-10 11:53:11

Co-authors: M. Inomoto, T. Yamada, H. Tanabe, P. Copinger, TS-Group

Contact Info:
University of Tokyo
7-3-1 Hongo
Bunkyo-ku, Tokyo   113-865
Japan

Abstract Text:
A series of reconnection heating have been demonstrated in TS-3, TS-4 and UTST experiments for the merging formation of Field-Reversed Configuration (FRC)[1,2] and Spherical Tokamak (ST)[3]. Cause and mechanism for the high-power reconnection heating are made clear by the new 2-D Doppler imaging measurement which is composed of three polychromators with ICCD cameras and 108 optical fibers. This 2-D ion temperature (Ti) measurement reveals two hot Ti spots in the downstream regions of reconnection. The bipolar reconnection outflow is observed to collide with the reconnected field lines surrounding the reconnection point. It forms steep jumps of electron density and magnetic field around the hot Ti spots, which satisfis the Rankin-Hugoniot relation. These facts indicate formation of fast the shock in the down-stream region similar to the solar flares[5]. The reconnection transforms a part of magnetic energy into the ion thermal energy probably due to the fast shock/ viscosity damping of reconnection outflow. The ion heating energy as well as the merging speed is observed to increase inversely with toroidal (guide) field component Bt. As Bt is decreased, ion gyroradius ρi increases and finally exceeds the sheet thickness δ during sheet compression by the CT/ ST merging. It causes a significant increase in effective resistivity of the current sheet[6], reconnection speed and outflow speed that directly determines the ion heating power of merging. These reconnection heating experiments are being upgraded to the ultra-high beta ST experiment: UTST with 1.2MW neutral beam (NB) and further to the largest ST merging experiment: MAST.

[1] Y. Ono, M. Yamada. et al., Phys. Rev. Lett. 76, 3328, (1996).
[2] E. Kawamori and Y. Ono, Phys. Rev. Lett 95, 085003, (2005).
[3] Y. Ono et al., Phys. Plasmas 7, 1863 (2001).
[4] Y. Ono et al., Nuclear Fusion, 43, 789, (2003).
[5] S. Masuda et al., Nature 371, 495 (1994).
[6] Y. Ono et al., Phys. Plasmas 4, 1953 (1997).

Characterization: A2,D6

Comments:
Characterization: A2, D6

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011