Investigation of Plasma Confirement of a Spherical Tokamak

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A spherical tokamak device named TST (the abbreviation of Tokyo Spherical Tokamak) had been constructed. It has been predicted theoretically that spherical tokamaks have the advantage of natural elongation, high beta, and MHD stability. We have gotten below-mentioned experimental results.1) A spherical tokamak device named TST had been constructed. A cylindrical vacuum vessel with 1.8m in diameter and 1.6m in height is employed. In the vessel, central core composed of ohmic coils and a part of toroidal coils is installed.2) A toroidal, ohmic and vertical coils had been designed and constructed. The toroidal field was 0.2 T in the center of the vacuum vessel and toroidal ripple was 2%. The flux swing of the ohmic coil was 15mVs.3) We got the plasma of 45 kA successfully. The value of plasma current is proportional to flux swing of ohmic coil and toroidal field.4) The time evolution of the shape of the plasma on a poloidal cross-section is investigated by the radiation measured with a PIN diode array. It was found that the aspect ratio reaches 1.3 at 70 mus from the start time of the discharge. The elongation was 1.8 at 90 mus from the start time of the discharge.5) We carried out a preliminary experiment on current drive due to electron gun. The electron beam of 1.7kA,1.5ms was gotten by the electron gun. It was found that the volt second consumption was reduced by factor 7.