Simulation of discharge initiation with runaway electrons in DIII-D

The fluid code STREAM [1] is validated using plasma startup experiments with a generation of runaway electrons (REs) on DIII-D. There is a high probability to produce REs during discharge initiation in ITER due to its limitations on the prefill pressure and breakdown electric field. This can lead to a range of negative outcomes, from a failed burn-through to a discharge where runaway current overcomes the ohmic current. To support an ITER Joint Activity on the discharge initiation scenario development, low-density ohmic plasma startup with generation of REs was studied on DIII-D. Effects of the prefill pressure, current ramp-up rate, electron density, and electron cyclotron heating were documented [2]. In this work, these experimental results are used to validate simulations by STREAM, a 0D code which self-consistently evolves the plasma density, temperature, and electric field, while accounting for the generation and loss of REs. The modeled RE current is compared with experimental estimations derived from MeV range gamma ray bremsstrahlung measurements. This result will be used to improve predictive tools for ITER and increase confidence in its operating scenario.



Work supported by US DOE under the Science Undergraduate Laboratory Internship (SULI) program, DE-SC0019003, and DE-FC02-04ER54698.



[1] M. Hoppe et al. J. Plasma Phys. (2022), vol. 88, 905880317

[2] See presentation by R. Xie, this meeting