Initial results of hard X-ray spectroscopy by LaBr3(Ce) detector for runaway electron study in Thailand Tokamak-1

Abstract

Thailand Tokamak-1 (TT-1) successfully achieved its first plasma operation in early 2023. Understanding the behavior of high-energy runaway electrons (RE) during plasma discharges is crucial in TT-1 due to the potential risk of significant damage to in-vessel components. To study the RE behavior and analyze its characteristics, the LaBr${}_3$(Ce) detector was employed for measuring hard X-ray emissions in TT-1. In this study, we first characterized the LaBr${}_3$(Ce) detector in the laboratory and then performed hard X-ray spectroscopy in TT-1. Calibration sources, including ¹³³Ba, ¹³⁷Cs, ²²Na, and ⁶⁰Co, with energies up to 1.33 MeV, were used in the laboratory. The detector was calibrated using biased high voltage of -1000 V. It was found to have an energy resolution of approximately 6.2% at an energy of 0.662 MeV. After calibration, the detector was installed at TT-1 to measure hard X-ray. We analyze the hard X-ray emission from discharge #2183 during a selected time interval. It is found that the high-energy hard X-ray emissions reach up to approximately 500 keV. Assuming a simple Maxwellian distribution of the RE population, their temperature is estimated to be $224\pm 5$ keV. These findings confirm the presence of high-energy runaway electrons during TT-1’s plasma discharges. However, to accurately derive the runaway electron energy spectrum from the hard X-ray energy spectrum, the unfolding technique is required. In future work, we plan to apply the unfolding method, conduct numerical simulations on the physics of runaway electrons, and employ Monte Carlo simulations on the hard X-ray emissions.