860 research outputs found
Comparison of runaway electron generation parameters in small, medium-sized and large tokamaks-A survey of experiments in COMPASS, TCV, ASDEX-Upgrade and JET
This paper presents a survey of the experiments on runaway electrons (RE) carried out
recently in frames of EUROFusion Consortium in different tokamaks: COMPASS, ASDEXUpgrade, TCV and JET. Massive gas injection (MGI) has been used in different scenarios for RE generation in small and medium-sized tokamaks to elaborate the most efficient and reliable ones for future RE experiments. New data on RE generated at disruptions in COMPASS
and ASDEX-Upgrade was collected and added to the JET database. Different accessible
parameters of disruptions, such as current quench rate, conversion rate of plasma current into runaways, etc have been analysed for each tokamak and compared to JET data. It was shown,
that tokamaks with larger geometrical sizes provide the wider limits for spatial and temporal
variation of plasma parameters during disruptions, thus extending the parameter space for
RE generation. The second part of experiments was dedicated to study of RE generation in
stationary discharges in COMPASS, TCV and JET. Injection of Ne/Ar have been used to
mock-up the JET MGI runaway suppression experiments. Secondary RE avalanching was
identified and quantified for the first time in the TCV tokamak in RE generating discharges
after massive Ne injection. Simulations of the primary RE generation and secondary
avalanching dynamics in stationary discharges has demonstrated that RE current fraction
created via avalanching could achieve up to 70–75% of the total plasma current in TCV.
Relaxations which are reminiscent the phenomena associated to the kinetic instability
driven by RE have been detected in RE discharges in TCV. Macroscopic parameters of RE
dominating discharges in TCV before and after onset of the instability fit well to the empirical
instability criterion, which was established in the early tokamaks and examined by results of
recent numerical simulations.EURATOM 633053Fundação para a Ciência e Tecnologia UID/FIS/50010/2013Ministry of Education and Science of the Russian Federation 14.619.21.0001, 15.08.2014, RFMEFI61914X000
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