R. Ishizaki et al.


MHD Simulation on Ablation Cloud in Tokamak and Heliotron

Date of publication:

Oct. 2006

Key words:

21 IAEA Fusion Energy Conference , TH/P3-6


It is well known that an ablation cloud drifts to the lower field side in tokamak plasmas, which leads to a good performance on fueling in tokamak. Such a good performance, however, has not been obtained yet in the planar axis heliotron; Large Helical Device (LHD) experiments, even if a pellet has been injected from the high field side. The purpose of the study is to clarify the difference on the cloud motion between tokamak and LHD plasmas by using the MHD simulation including ablation processes. It is found in tokamaks that the drift motion is induced by a tire tube force and 1/R force in the major radius direction, and that the pressure and density of the plasmoid have oscillation due to fast compressional Alfven wave. The first trial simulations on the motion of the plasmoid in a straight helical and LHD plasmas also show that the plasmoid drifts to the lower field side similarly to tokamaks. However, an plasmoid drifts inward or outward of the flux surfaces depending on the location along the magnetic field lines, since the plasmoid expands along the magnetic field with time, the magnetic field strength and the direction of the magnetic curvature change along the magnetic field lines due to both toroidicity and helicity of the helical coils, and the rotational transform is greater than that in tokamaks in the plasma periphery. Thus, it is suggested that the difference of the pellet injections between the high field and the low field sides is reduced in helical plasmas.

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