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Report No.

Nonlinear variational method for predicting fast collisionless magnetic reconnection

Hirota, Makoto; Morrison, P. J.*; Ishii, Yasutomo; Yagi, Masatoshi; Aiba, Nobuyuki

A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges. Explosive growth of the tearing mode driven by electron inertia is analytically estimated by using an energy principle with a nonlinear displacement map. Decrease of the potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in accelerated reconnection. Release of free energy by such ideal fluid motion leads to unsteady and strong convective flow, which is not deterred by the small dissipation effects in high-temperature tokamak plasmas. Direct numerical simulation in slab geometry substantiates the theoretical prediction of the nonlinear growth.



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Category:Physics, Fluids & Plasmas



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