| 1. |
- Stahl, Adam, 1985, et al.
(author)
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Kinetic modelling of runaway electrons in dynamic scenarios
- 2016
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 56:11, s. 112009-
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Journal article (peer-reviewed)abstract
- Improved understanding of runaway-electron formation and decay processes are of prime interest for the safe operation of large tokamaks, and the dynamics of the runaway electrons during dynamical scenarios such as disruptions are of particular concern. In this paper, we present kinetic modelling of scenarios with time-dependent plasma parameters; in particular, we investigate hot-tail runaway generation during a rapid drop in plasma temperature. With the goal of studying runaway-electron generation with a self-consistent electric-field evolution, we also discuss the implementation of a conservative collision operator and demonstrate its properties. An operator for avalanche runaway-electron generation, which takes the energy dependence of the scattering cross section and the runaway distribution into account, is investigated. We show that the simpler avalanche model of Rosenbluth & Putvinskii [Nucl. Fusion 37, 1355 (1997)] can give very inaccurate results for the avalanche growth rate (either lower or higher) for many parameters, especially when the average runaway energy is modest, such as during the initial phase of the avalanche multiplication. The developments presented pave the way for an improved modelling of runaway-electron dynamics during disruptions or other dynamic events.
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| 2. |
- Stahl, Adam, 1985, et al.
(author)
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Runaway-electron formation and electron slide-away in an ITER post-disruption scenario
- 2016
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 775:1
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Conference paper (peer-reviewed)abstract
- Mitigation of runaway electrons is one of the outstanding issues for a reliable operation of ITER and other large tokamaks, and accurate estimates for the expected runaway- electron energies and current are needed. Previously, linearized tools, assuming the runaway population to be small, have been used to study the runaway dynamics, but these tools are not valid in the cases of most interest, i.e. when the runaway population becomes substantial. We study runaway-electron formation in a post-disruption ITER plasma using the newly developed non-linear code NORSE , and nd that the entire electron population is converted to runaways in the scenario considered. A new non-linear feedback mechanism is also described, by which a transition to electron slide-away can be induced at eld strengths signi cantly lower than previously expected. We nd the exact time to the transition to be highly dependent on the details of the mechanisms removing heat from the thermal electron population.
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| 3. |
- Wilkie, George, 1983, et al.
(author)
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Transport and deceleration of fusion products in microturbulence
- 2016
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In: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:6, s. 060703-
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Journal article (peer-reviewed)abstract
- The velocity-space distribution of alpha particles born in fusion devices is subject to modification at moderateenergies due to turbulent transport. Therefore, one must calculate the evolution of an equilibrium distributionwhose functional form is not known a priori. Using a novel technique, applicable to any trace impurity, wehave made this calculation for fully nonlinear gyrokinetic simulations not only possible, but particularlyefficient. We demonstrate a microturbulence-induced departure from the local slowing-down distribution, aninversion of the energy distribution, and associated modifications to the alpha heating and pressure profilesin an ITER-like scenario.
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