Efficient lasing in mixtures of helium and fluorine in diffuse discharges formed by runaway electrons

2020 ◽  
Vol 50 (10) ◽  
pp. 900-903
Author(s):  
V F Tarasenko ◽  
A N Panchenko ◽  
V V Kozhevnikov
Keyword(s):  
Runaway Electrons ◽  
Efficient Lasing

scholarly journals Spatiotemporal analysis of the runaway distribution function from synchrotron images in an ASDEX Upgrade disruption

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
M. Hoppe ◽  
L. Hesslow ◽  
O. Embreus ◽  
L. Unnerfelt ◽  
G. Papp ◽  
...  
Keyword(s):  
Radial Profile ◽  
Spatiotemporal Analysis ◽  
High Energy ◽  
Synchrotron Emission ◽  
Analytic Model ◽  
Runaway Electrons ◽  
Radial Density ◽  
Radial Density Profile ◽  
Argon Injection ◽  
Seed Population

Synchrotron radiation images from runaway electrons (REs) in an ASDEX Upgrade discharge disrupted by argon injection are analysed using the synchrotron diagnostic tool Soft and coupled fluid-kinetic simulations. We show that the evolution of the runaway distribution is well described by an initial hot-tail seed population, which is accelerated to energies between 25–50 MeV during the current quench, together with an avalanche runaway tail which has an exponentially decreasing energy spectrum. We find that, although the avalanche component carries the vast majority of the current, it is the high-energy seed remnant that dominates synchrotron emission. With insights from the fluid-kinetic simulations, an analytic model for the evolution of the runaway seed component is developed and used to reconstruct the radial density profile of the RE beam. The analysis shows that the observed change of the synchrotron pattern from circular to crescent shape is caused by a rapid redistribution of the radial profile of the runaway density.

scholarly journals Effects of magnetic perturbations and radiation on the runaway avalanche

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
P. Svensson ◽  
O. Embreus ◽  
S. L. Newton ◽  
K. Särkimäki ◽  
O. Vallhagen ◽  
...  
Keyword(s):  
Growth Rate ◽  
Runaway Electrons ◽  
Plasma Parameters ◽  
Perturbative Approach ◽  
Efficient Simulation ◽  
Strong Current ◽  
Magnetic Perturbations ◽  
Space Dynamics ◽  
Stochastic Magnetic Fields ◽  
Mitigation Methods

The electron runaway phenomenon in plasmas depends sensitively on the momentum- space dynamics. However, efficient simulation of the global evolution of systems involving runaway electrons typically requires a reduced fluid description. This is needed, for example, in the design of essential runaway mitigation methods for tokamaks. In this paper, we present a method to include the effect of momentum-dependent spatial transport in the runaway avalanche growth rate. We quantify the reduction of the growth rate in the presence of electron diffusion in stochastic magnetic fields and show that the spatial transport can raise the effective critical electric field. Using a perturbative approach, we derive a set of equations that allows treatment of the effect of spatial transport on runaway dynamics in the presence of radial variation in plasma parameters. This is then used to demonstrate the effect of spatial transport in current quench simulations for ITER-like plasmas with massive material injection. We find that in scenarios with sufficiently slow current quench, owing to moderate impurity and deuterium injection, the presence of magnetic perturbations reduces the final runaway current considerably. Perturbations localised at the edge are not effective in suppressing the runaways, unless the runaway generation is off-axis, in which case they may lead to formation of strong current sheets at the interface of the confined and perturbed regions.

Development of a hard X-ray detector for measuring continuous spectra generated by runaway electrons in VEST

2021 ◽  
Vol 170 ◽  
pp. 112522
Author(s):  
Soobin Lim ◽  
Jonggab Jo ◽  
Changwook Koo ◽  
Sung-Joon Ye ◽  
Kyoung-Jae Chung ◽  
...  
Keyword(s):  
Runaway Electrons ◽  
X Ray

Suppression of runaway electron generation by massive helium injection after induced disruptions on TEXTOR

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
A. Lvovskiy ◽  
H. R. Koslowski ◽  
L. Zeng ◽  
Keyword(s):  
Time Delay ◽  
Runaway Electron ◽  
Critical Density ◽  
Runaway Electrons ◽  
Electron Generation ◽  
Disruption Mitigation ◽  
Order Of Magnitude ◽  
Short Time ◽  
Short Time Delay

Disruptions with runaway electron generation have been deliberately induced by injection of argon using a disruption mitigation valve. A second disruption mitigation valve has been utilised to inject varying amounts of helium after a short time delay. No generation of runaway electrons has been observed when more than a critical amount of helium has been injected no later than 5 ms after the triggering of the first valve. The required amount of helium for suppression of runaway electron generation is up to one order of magnitude lower than the critical density according to Connor & Hastie (1975) and Rosenbluth & Putvinski (1997).

High pressure gas injection for suppression of runaway electrons in disruptions

2011 ◽  
Author(s):  
L.E. Zakharov ◽  
S. Putvinski ◽  
A.S. Kukushkin ◽  
R.A. Pitts ◽  
M. Sugihara ◽  
...  
Keyword(s):  
High Pressure ◽  
Gas Injection ◽  
Runaway Electrons

Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field

2012 ◽  
Vol 109 (8) ◽  
Author(s):  
A. V. Gurevich ◽  
G. A. Mesyats ◽  
K. P. Zybin ◽  
M. I. Yalandin ◽  
A. G. Reutova ◽  
...  
Keyword(s):  
Electric Field ◽  
Strong Electric Field ◽  
Runaway Electrons
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