Local Stability of High Beta Low Aspect Ratio Tokamak with Negative Shear

概要

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Magnetohydrodynamic(MHD)equilibrium and local stability are studied for low aspect ratio tokamaks with an aspect ratio A=1.25. Particular interest is in equilibria with substantial negative shear region. Almost all MHD equilibria with negative shear region are paramagnetic for low aspect ratio tokamaks. Shafranov shift is reduced in case of the negative shear for the same q_min and it becomes difficult to produce a region with a closed |B|=const. surface, which is favorable for particle confinement under the effect of toroidal ripples, even for β(0)≃50%. Here q_min is the minimum value of safety factor and β(0)is a central beta value. Mercier criterion is checked for MHD equilibria obtained with the VMEC(Variational Moment Equilibrium Code)by changing ellipticity and triangularity. A low aspect ratio configuration with a moderate triangularity is proposed to obtain a high plasma current in a high beta plasma, which has an advantage to confine charged fusion products.
社団法人プラズマ・核融合学会の論文
1998-06-25