Energetic electron trapping in magnetic islands in magnetized plasma*

We report on the experimental observation of 10MeV electron trapping in resonant magnetic perturbation (RMP) islands in DIII-D. We examine low density, inner-wall limited L-mode discharges where energetic electrons are commonly observed to form. RMP coils were used to grow magnetic islands at the n=1 rational surfaces, i.e., at safety factor ratios q=m/n, where n=1 and m is an integer. Electron cyclotron heating and current drive (ECH/ECCD) pulses were used to induce small perturbations of the electron distribution functions within locations inside and outside the islands. The perturbations were detected on several diagnostics including electron cyclotron emission, hard X-ray emission, and synchrotron emission. The data reveals the formation of 10MeV electrons at the beginning of the discharge, followed by electron trapping in the q=1 and q=2 islands once the RMP coils are turned on. The islands are then rotated to assess stability of the electron trapping. These results agree with spacecraft data suggesting that energetic electrons originate from magnetic islands in the Earth's magnetosphere during geomagnetic storms.