Speaker
Description
See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1015.pdf
The production of relativistic runaway electrons during disruptions can potentially compromise the integrity of plasma-facing-components in large tokamaks. In ITER up to 70% of the initial plasma current can be converted into relativistic runaway current. The energy content of such runaway electron beam can reach several tens of Megajoules. If untamed, a runaway electron beam colliding with the first wall can melt several kilograms of material in a single event, posing a significant threat to the machine [1]. Runaway electron production, control and mitigation is therefore currently one of the main topics studied in midsize and large-scale tokamaks.
A variety of diagnostic techniques are employed to characterize the runaway electron population. If the runaway electron beam remains well confined during the disruption, information on the runaway electron energy distribution can be extracted by measuring the bremsstrahlung radiation emitted by the interaction between the beam and the post disruption plasma. In order to do this, it is necessary to build a custom high counting rate (> 1MHz) gamma-ray spectrometer that can reliably measure the bremsstrahlung spectrum up to tens of MeV and a suitable deconvolution code that can retrieve the runway electron distribution from the measured spectrum.
In this work, we discuss the design of a new gamma-ray spectrometer optimized for runaway electrons bremsstrahlung emission. The detector is made of a LaBr3:Ce scintillator crystal coupled to a photomultiplier tube. An improved acquisition system allows for continuous data collection. This device was used to measure the gamma-ray emission during the 2019 runaway electron experiments at Asdex Upgrade. Results achieved are promising for inferring information on the high energy component of the runaway electron distribution in tokamaks.
[1] Hender TC, Wesley JC et al., Nuclear Fusion 47 (2007) S128-S202.
