| 1. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Effect of plasma elongation on current dynamics during tokamak disruptions
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- Plasma terminating disruptions in tokamaks may result in relativistic runaway electron beams with potentially serious consequences for future devices with large plasma currents. In this paper, we investigate the effect of plasma elongation on the coupled dynamics of runaway generation and resistive diffusion of the electric field. We find that elongated plasmas are less likely to produce large runaway currents, partly due to the lower induced electric fields associated with larger plasmas, and partly due to direct shaping effects, which mainly lead to a reduction in the runaway avalanche gain. © Cambridge University Press 2020.
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| 2. |
- Hoppe, Mathias, 1993, et al.
(författare)
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Runaway electron synchrotron radiation in a vertically translated plasma
- 2020
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 60:9
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Tidskriftsartikel (refereegranskat)abstract
- Synchrotron radiation observed from runaway electrons (REs) in tokamaks depends upon the position and size of the RE beam, the RE energy and pitch distributions, as well as the location of the observer. We show experimental synchrotron images of a vertically moving RE beam sweeping past the detector in the Tokamak a Configuration Variable (TCV) tokamak and compare it with predictions from the synthetic synchrotron diagnosticSoft. This experimental validation lends confidence to the theory underlying the synthetic diagnostics which are used for benchmarking theoretical models of and probing runaway dynamics. We present a comparison of synchrotron measurements in TCV with predictions of kinetic theory for runaway dynamics in uniform magnetic fields. We find that to explain the detected synchrotron emission, significant non-collisional pitch angle scattering as well as radial transport of REs would be needed. Such effects could be caused by the presence of magnetic perturbations, which should be further investigated in future TCV experiments.
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| 3. |
- Insulander Björk, Klara, 1982, et al.
(författare)
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Kinetic modelling of runaway electron generation in argon-induced disruptions in ASDEX Upgrade
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- Massive material injection has been proposed as a way to mitigate the formation of a beam of relativistic runaway electrons that may result from a disruption in tokamak plasmas. In this paper we analyse runaway generation observed in eleven ASDEX Upgrade discharges where disruption was triggered using massive gas injection. We present numerical simulations in scenarios characteristic of on-axis plasma conditions, constrained by experimental observations, using a description of the runaway dynamics with a self-consistent electric field and temperature evolution in two-dimensional momentum space and zero-dimensional real space. We describe the evolution of the electron distribution function during the disruption, and show that the runaway seed generation is dominated by hot-tail in all of the simulated discharges. We reproduce the observed dependence of the current dissipation rate on the amount of injected argon during the runaway plateau phase. Our simulations also indicate that above a threshold amount of injected argon, the current density after the current quench depends strongly on the argon densities. This trend is not observed in the experiments, which suggests that effects not captured by zero-dimensional kinetic modelling - such as runaway seed transport - are also important.
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| 4. |
- Särkimäki, Konsta, 1990, et al.
(författare)
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Assessing energy dependence of the transport of relativistic electrons in perturbed magnetic fields with orbit-following simulations
- 2020
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 60:12
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Tidskriftsartikel (refereegranskat)abstract
- Experimental observations, as well as theoretical predictions, indicate that the transport of energetic electrons decreases with energy. This reduction in transport is attributed to finite orbit width (FOW) effects. Using orbit-following simulations in perturbed tokamak magnetic fields that have an ideal homogeneous stochastic layer at the edge, we quantify the energy dependence of energetic electrons transport and confirm previous theoretical estimates. However, using magnetic configurations characteristic of JET disruptions, we find no reduction in runaway electron transport at higher energies, which we attribute to the mode widths being comparable to the minor radius, making the FOW effects negligible. Instead, the presence of islands and non-uniform magnetic perturbations are found to be more important. The diffusive-advective transport coefficients calculated in this work, based on simulations for electron energies 10 keV-100 MeV, can be used in integrated disruption modelling to account for the transport due to the magnetic field perturbations.
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| 5. |
- Vallhagen, Oskar, 1997, et al.
(författare)
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Runaway dynamics in the DT phase of ITER operations in the presence of massive material injection
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:4
-
Tidskriftsartikel (refereegranskat)abstract
- A runaway avalanche can result in a conversion of the initial plasma current into a relativistic electron beam in high-current tokamak disruptions. We investigate the effect of massive material injection of deuterium-noble gas mixtures on the coupled dynamics of runaway generation, resistive diffusion of the electric field and temperature evolution during disruptions in the deuterium-tritium phase of ITER operations. We explore the dynamics over a wide range of injected concentrations and find substantial runaway currents, unless the current quench time is intolerably long. The reason is that the cooling associated with the injected material leads to high induced electric fields that, in combination with a significant recombination of hydrogen isotopes, leads to a large avalanche generation. Balancing Ohmic heating and radiation losses provides qualitative insights into the dynamics; however, an accurate modelling of the temperature evolution based on energy balance appears crucial for quantitative predictions.
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