Measurement of the non-thermal bremsstrahlung emission between 20 and 7000 keV in the HT-7 Tokamak

Hard X-ray (HXR) emission in the energy range of 20–7000 keV during lower hybrid current drive (LHCD) experiments in the HT-7 superconducting tokamak has been measured. A vertical multi-channel CdTe detector array is used to measure the fast electron bremsstrahlung (FEB) emission in the energy range 20–300 keV. Three tangentially arranged NaI detectors are used to measure the HXR emission in the energy range 500–7000 keV. In LHCD plasmas with non-zero loop voltage, the fast electron tail extends out to several hundreds keV. The energetic tail acts as seeds of runaways in high loop voltage environments. In this paper, the diagnostics system is described, and the dynamics of runaways in LHCD discharges is presented by the combination of FEB and energetic HXR measurements.