Assessment of plasma performance in a magnetic configuration with reduced poloidal coils for a helical DEMO reactor FFHR-d1

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 Cexp used in the direct profile extrapolation (DPE) method is smaller in the vertically elongated configuration, where Cexp is proportional to the reactor size, Rreactor, at a given reactor magnetic field, Breactor, i.e., Rreactor ∝ CexpBreactor-4/3. The difference in Cexp 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. © 2012 The Japan Society of Plasma Science and Nuclear Fusion Research.