This paper reports on the experimental observation and numerical reconstruction of island-like structures in synchrotron imaging emitted by runaway electrons (REs) on Experimental Advanced Superconducting Tokamak. During low-density ohmic discharges with external resonant magnetic perturbations, island-like structures were observed in the synchrotron radiation emitted by REs. Through simulations based on relativistic guiding-center motion equations and a cone radiation model, it was found that these island-like structures in synchrotron imaging are related to the island-like spatial distribution of REs. The island-like spatial distribution might be caused by the sticky regions in the stochastic field. Appropriate projection is necessary for island-like structures in synchrotron imaging. The study provides insights into the behavior of REs in perturbation magnetic fields and offers a sign for the existence of sticky regions within stochastic fields. Besides, discrepancies between simulation and experimental results suggest that non-linear plasma response should be considered. This research improves our understanding of RE behavior in perturbed fields and has implications for the development of effective RE mitigation strategies in large-scale tokamaks.
This paper reports the observation and simulation of island-like structures in synchrotron radiation emitted by runaway electrons on the EAST tokamak. The island-like structures are related to the spatial distribution of runaway electrons, which may be caused by sticky regions in the stochastic magnetic field. The study provides insights into runaway electron behavior in perturbed fields and has implications for developing effective runaway electron mitigation strategies.