Hard X-ray Bremsstrahlung of relativistic Runaway Electrons in JET

Abstract

One of the main requirements to the Disruption Mitigation System (DMS) in International Thermonuclear Experimental Reactor (ITER) is a reliable capability to avoid/suppress a detrimental runaway electron (RE) generation during disruptions. An understanding of the physics of RE is a key factor for design of ITER DMS with necessary properties on RE suppression. RE interacting with plasma particles and hitting the plasma-facing components (PFCs) produce a bremsstrahlung in MeV energy range (hard X-rays (HXR) and γ-rays) and photo-neutrons. Measurements of produced HXR/γ-rays and photo-neutrons provide detailed information on RE generation and serve as a main tool for runaway physics study in JET. This report presents recent progress in development of the JET diagnostic techniques for registering of the HXR/γ-rays emission and improvement of HXR data analysis methods for RE studies. The HXR spectra have been measured with the sets of HXR spectrometers. This data was numerically processed using special de-convolution procedure allowing a study of evolution of the RE Distribution Function (REDF). Maximal and mean energies of RE populations have been calculated. As well, the detection of spatial distribution of HXR sources in JET plasmas with the JET neutron/γ-rays profile monitor allowed the mapping of RE beams spatial evolution during RE plateaus. In order to increase the HXR/γ-rays diagnostic performance in future JET experiments, the vertical slow spectrometers will be replaced by high-speed LaBr3(Ce) spectrometers allowing measurements with counting rate up to 5*106 sec−1. Also spectrometer with tangential LoS will be replaced by a couple of LaBr3(Ce) and CeBr3 spectrometers. CsI(Tl) detectors in γ-cameras will be substituted by LaBr3(Ce) and CeBr3 crystals coupled with up-to-date SiPM light detectors, which allowed increasing the counting rate of the γ-camera detectors by an order of 10.