Ripple induced diffusion of fast ions in tokamaks with an elliptic cross-section

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Abstract
The diffusion of high energy ions caused by toroidal magnetic field ripple in a tokamak with flux surfaces of elliptical cross-section is studied. It is shown that the elongation of the cross-section increases the characteristic ripple value above which the collisionless motion of the trapped particles becomes stochastic. The elongation also results in a reduction of the diffusion coefficient, both in the regime of collisionless (intrinsic) stochasticity and in various collisional regimes. It is further shown that in an elliptical tokamak the energy range in which the weak collision regime is achieved is narrowed, and the range characterized by ripple-plateau diffusion is broadened. The distribution of the fast ion flux to the wall is also considered.