Generation and dissipation of runaway electrons in ASDEX Upgrade experiments

Abstract

The paper describes under which plasma and machine conditions runaway electrons (REs) are generated during ASDEX Upgrade plasma disruptions. The REs are created by argon injection to investigate methods of current and energy dissipation. The RE beams are stable and last up to a few hundred milliseconds. The experimental findings are described and made available for the validation of theoretical models. In the following, a simple 0D fluid model is used to simulate the observed RE current magnitude and time behavior. In spite of its simplicity, the model is consistent with the measured RE current. The injection of heavy gases into the RE beam is then discussed in some detail: the injected gas penetrates into the low density background plasma and through the beam without ionizing significantly. Therefore its effect on the REs can be tested directly and it is found to be consistent with the known Coulomb collisional theory.