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Assessment of Plasma Performance in a Magnetic Configuration with Reduced Poloidal Coils for a Helical DEMO Reactor FFHR-d1

Junichi MIYAZAWA, Takuya GOTO, Ryuichi SAKAMOTO, Gen MOTOJIMA, Chihiro SUZUKI, Tomohiro MORISAKI, Suguru MASUZAKI, Ichihiro YAMADA, Hiroshi YAMADA, Akio SAGARA and the FFHR Design Group

National Institute for Fusion Science, Toki, Gifu 509-5292, Japan

(Received 6 December 2011 / Accepted 2 March 2012 / Published 26 July 2012)

Abstract

The performance of high-density plasmas heated by neutral beam (NB) injection in a vertically elongated configuration using four poloidal coils has been investigated in LHD and shown to be better than that in the normal configuration using six poloidal coils. Reduction of poloidal coils is favorable in designing an LHD-type helical reactor FFHR-d1, from both points of view of cost reduction and realization of large maintenance ports. In the experiment, no clear difference between the two configurations was recognized in the relation between the central density and the central pressure. Meanwhile, a factor C_exp used in the direct profile extrapolation (DPE) method is smaller in the vertically elongated configuration, where C_exp is proportional to the reactor size, R_reactor, at a given reactor magnetic field, B_reactor, i.e., R_reactor ∝ C_expB_reactor^−4/3. The difference in C_exp between the two configurations is enhanced to > 10 % as the plasma beta increases. This might be due to the larger plasma volume and/or the mitigated Shafranov shift in the vertically elongated configuration.

Copyright (c) 2012 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

heliotron, LHD, FFHR-d1, energy confinement scaling, vertical elongation, reactor design

DOI: 10.1585/pfr.7.2402072

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This paper may be cited as follows:

Junichi MIYAZAWA, Takuya GOTO, Ryuichi SAKAMOTO, Gen MOTOJIMA, Chihiro SUZUKI, Tomohiro MORISAKI, Suguru MASUZAKI, Ichihiro YAMADA, Hiroshi YAMADA, Akio SAGARA and the FFHR Design Group, Plasma Fusion Res. 7, 2402072 (2012).