Results of the Excitation Test of the LHD Helical Coils Cooled by Subcooled Helium

S Imagawa,T Mito,S Hamaguchi,N Yanagi,H Sekiguchi,O Motojima,S Moriuchi,A Komori,K Ooba,T Okamura,T Obana

doi:10.1109/tasc.2008.921977

Abstract

Large helical device, the largest superconducting stellarator, has been operated for the research of fusion plasma since 1998. The toroidal field of almost 3 T is produced by a pair of pool-cooled helical coils, in the innermost layers of which a normal-zone had been induced several times at the bottom of the coil at higher currents than 11.0 kA. Since the field is not the highest there, the local cooling conditions are probably deteriorated by bubbles gathered by buoyancy. In order to improve the cryogenic stability by subcooling, an additional cooler with two-stage cold compressors was installed at the inlet of the coil in 2006. The inlet and outlet temperatures of the coils were successfully lowered to 3.2 K and 3.8 K, respectively, with a mass flow of 50 g/s. In spite of a half charging rate to reduce AC losses, a normal-zone was induced near the top of the coil at 11.45 kA. It propagated to one side and stopped near the inner equator, where the field is the highest. In comparison with the stability tests with a model coil, the local temperatures of the innermost layers near the top is considered to have been raised up to almost the saturated temperature of 4.4 K by charging. The excitation method was revised to waiting cool-down at 11.0 kA, and the excitations up to 11.5 kA have been attained.

Highlights

The present status of nonneutral plasma science is reviewed with a particular interest in the pursuit of a new frontier for plasma physicists engaged in basic researches
Leaving most of topics to the cited references, the author describes characteristic features of nonneutral plasmas appearing in distinct confinement properties, equilibria, transport, nonlinear evolution of Kelvin-Helmholtz instability, and fluid echo phenomena
These examples may convey the significance of nonneutral plasma science as one of newly-rising branches of plasma physics and as a potentially relevant channel through which plasma physics could explore new dimensions

Summary

Introduction

The present status of nonneutral plasma science is reviewed with a particular interest in the pursuit of a new frontier for plasma physicists engaged in basic researches. Leaving most of topics to the cited references, the author describes characteristic features of nonneutral plasmas appearing in distinct confinement properties, equilibria, transport, nonlinear evolution of Kelvin-Helmholtz instability, and fluid echo phenomena. の図書室で新着書欄に置かれた R.C. Davidson 著 Theory of Nonneutral Plasmas[1]を目にしたときであったと思

Results

Conclusion