Characterization and Mitigation of Runaway Electrons in the Compact Toroidal Hybrid Experiment

The Compact Torodial Hybrid Experiment (CTH) at Auburn University has historically generated high X-ray dosages in the surrounding facility. The radiation profile has been characterized by correlation experiments using a pair of scintillators, which have measured X-ray energies in the range of 500 KeV to 10 MeV. It was determined that the X-rays are produced by runaway electrons which emit radiation from relativistic bremsstrahlung while trapped in confining magnetic fields at the end of the plasma discharge. The runaway electron populations and X-ray emissions have been studied across a range of CTH magnetic configurations with varying rotational transforms and field strengths. Variations in the magnetic configuration have been found to have a strong impact on runaway generation and the emission structure. Emission mitigation strategies have been developed and tested which minimize the runaway electron source, and have demonstrated that the X-ray production can be reduced over 90% by altering the magnetic surfaces and neutral gas feed post discharge. In addition, a method was developed which used the observed emission spectrum to model the performance of radiation shielding and inform shielding installation in the facility. Finally, a real-time X-ray monitoring system was installed to record and report future emissions.