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icc2011_paper.pdf2011-09-05 08:45:29Toru Ii
a0poster.pdf2011-08-26 21:53:42Toru Ii

Merging Formation of Oblate Field-Reversed Configurations with the Assistance of Neutral Beam Injection

Author: Toru Ii
Requested Type: Poster Only
Submitted: 2011-07-07 18:43:58

Co-authors: K.Gi, T.Umezawa, M.Inomoto,Y.Ono

Contact Info:
The University of Tokyo
2-11-16 Yayoi
Bunkyo-ku, Tokyo   113-003
Japan

Abstract Text:
The effect of energetic beam ions on oblate Field-Reversed Configurations (FRCs) has been studied experimentally in the TS-4 plasma merging device. An important question is whether plasma flows and large ion gyroradii generated by beam ions can stabilize the global modes essential to large size (R ~ 0.5 m) FRCs. In order to examine the kinetic effects, we developed an economical high-power pulsed Neutral Beam Injection (NBI) system by use of a washer gun plasma source, eliminating the conventional filaments and water cooling system. We obtained the maximum beam power up to 0.6 MW (15 kV, 40 A) and the pulse length over 0.5 ms, longer than the FRC lifetime in TS-4. The Monte Carlo simulation for the tangential co-current NB injection indicates that the beam ions are trapped between the magnetic axis and the separatrix. A new finding is that two merging high-s hydrogen spheromaks with opposite helicities relax into the large scale FRC with poloidal flux as high as 15 mWb under the assistance of the 0.6 MW NBI. Here, s is plasma size normalized by ion gyroradius. However, they did not relax to an FRC without the assistance of NBI. These facts suggest some ion kinetic effect such as toroidal ion flow is essential to FRC stability. Effect of high energy beam on parameter s of FRCs will be a key to solve the unknown FRC stability. Recently, two new NB sources with acceleration voltage and current of 15 kV and 20 A were installed on the TS-4 device on the midplane for tangential injection. We will start the upgraded FRC experiments with NBI power of 1 MW.

Characterization: A3,D6

Comments:

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