Experiments of Plasma Current Start-Up in Tokamak-Helical Hybrid Device TOKASTAR-2

概要

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The small device named TOKASTAR-2 has tokamak-helical hybrid coils to generate both configurations independently. We produced pre-ionized plasma with simple toroidal field in this TOKASTAR-2, and the spatial profiles of electron temperature and density were measured, which suggests both fundamental ECR heating process and other heating mechanisms. Within the limitation of static vertical field, around 0.1 kA plasma current was induced with strongly inward shifted configuration observed by the fast camera measurement, which is verified by the TOSCA equilibrium analysis. It was found that the eddy currents on the vacuum chamber prevent the plasma current build-up. The preliminary application of outer helical field was tried and the plasma current reduction was observed. For the optimization of tokamak operation to drive 1 kA plasma current, time-varying vertical field coil currents and eddy currents were evaluated by the TOSCA code, and the necessity of in-vessel vertical field coils was clarified. The pure current-less TOKASTAR configuration will be demonstrated by installing additional helical coils in the future.