Single Particle Modeling of Electron Diffusion in Magnetized Plasmas with Magnetic Islands

Recent DIII-D experiments demonstrated that magnetic islands can trap 10 MeV energetic electrons (EEs). Synchrotron emission camera data suggests that during the trapping, the emission from the EE cloud becomes brighter, which can result from increased density or acceleration of the EEs inside the island. To investigate these processes, a random kick algorithm is implemented in the TRIP3D-GPU field line tracing code. In this model, the motion of a test electron is assumed to be driven by the magnetic field line topology corresponding to the DIII-D experiments including the effects of radial magnetic perturbations, error fields, and error field corrections from the various DIII-D coil sets. To model a collision between the electron and a background ion, a random number is sampled from a Poisson distribution. To study the role of island topology, tracer electrons are launched from different starting points near island O-points and X-points. Then, the distribution of end locations (originating from the same starting point) is examined to assess the relative probability of the electron residence location at the end of the simulation. Initial comparison of the results against the experimental observations confirms increased probability for electron trapping near island O-points.