Simulation of runaway electron orbit loss in an ITER-like equilibrium

Matsuyama, Akinobu; Yagi, Masatoshi; Kagei, Yasuhiro*

Relativistic orbit-following code ETC-Rel is developed to study runaway electron dynamics in magnetic turbulence during tokamak disruptions. The code is applied to up-down asymmetric equilibrium like ITER, where relativistic drift equations are formulated on the basis of the Euler-Lagrange equations in Boozer coordinates especially taking into account loop voltage. For ITER-scale machines, since the ratio of poloidal gyroradius to the device size is much smaller than unity, the distortion of electron orbit with respect to the field-line trajectories is negligible. It indicates that enhancement of magnetic stochasticity due to overlapping of magnetic islands is essential for the degradation of runaway electron confinement. Simulations are used to calculate the mean-square displacement of test particles in magnetic turbulence, showing nondiffusive nature of the radial transport of runaway electrons.