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(EXP4/10) Helicty Injection Current Drive of Spherical Tokamak & Spheromak Plasmas in HIST

   
M. Nagata , M. Haruoka , S. Kano , N. Yuasa , N. Fukumoto , T. Uyama 
 
Faculty of Engineering, Himeji Institute of Technology, Shosha, Himeji, Hyogo, Japan

Abstract
In the Helicity Injected Spherical Torus (HIST) device, spherical torus (ST) plasmas with 100 kA toroidal currents have been successfully sustained by coaxial helicity injection. Internal magnetic configurations with the closed poloidal flux of helicity-driven ST plasmas have been revealed by intensive internal magnetic measurements. As the configuration approaches a tokamak from a spheromak, the n = 1 mode being essential for current drive becomes less effective, resulting in the flux amplification level being decreased although the total toroidal current has increased. The transition from a hollow current profile to a peaked one in the tokamak operation has been observed for the first time during the helicity injection process. This may be explained by an Ohmic induction effect using the open flux column.

     

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IAEA 1999