Global stability study of the ultralow aspect ratio tokamak, ULART

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Abstract
By introducing a slender current carrying conductor through the geometric centre axis of the TS-3 device at Tokyo University, ultralow aspect ratio tokamak (ULART) configurations have been generated with aspect ratios as low as 1.1. In this extreme limit the transition of the spheromak (qedge=0, Itf=0) to an ULART plasma (qedge=2-20) is studied. The global MHD characteristics of ULART are investigated by comparing the theoretical results with the experimental data obtained. A small current (compared with the plasma current) in the centre conductor is found to improve significantly the global MHD stability characteristics of the plasmas formed by effectively stabilizing the global tilt/shift mode. Theoretical calculations of the threshold toroidal field current required for stability and the growth rates of the tilt/shift modes agree well with the TS-3 data