| 1. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Kinetic modelling of runaways in fusion plasmas
- 2016
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Ingår i: Proceedings of 26th IAEA Fusion Energy Conference, Kyoto, Japan. ; , s. TH/P4-1
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mitigation of runaway electrons is one of the outstanding issues for a reliable operationof ITER and other large tokamaks. To achieve this, quantitatively accurate estimatesfor the expected runaway electron energies and current are needed. In this work we de-scribe an accurate theoretical framework for studying the effects of collisional nonlinear-ities, bremsstrahlung and synchrotron radiation emission, and knock-on collisions on therunaway electron distribution. We outline the identification of significant features of run-away electron behaviour enabled by this framework and their potential to affect the growthof a runaway population.
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| 2. |
- Pusztai, Istvan, 1983, et al.
(författare)
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Turbulent transport of MeV range cyclotron heated minorities as compared to alpha particles
- 2016
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 58:10, s. 105001-
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Tidskriftsartikel (refereegranskat)abstract
- We study the turbulent transport of an ion cyclotron resonance heated (ICRH), MeV range minority ion species in tokamak plasmas. Such highly energetic minorities, which can be produced in the three ion minority heating scheme (Kazakov et al (2015) Nucl. Fusion 55 032001), have been proposed to be used to experimentally study the confinement properties of fast ions without the generation of fusion alphas. We compare the turbulent transport properties of ICRH ions with that of fusion born alpha particles. Our theoretical predictions indicate that care must be taken when conclusions are drawn from experimental results: while the effect of turbulence on these particles is similar in terms of transport coefficients, differences in their distribution functions — ultimately their generation processes — make the resulting turbulent fluxes different.
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| 3. |
- Paz-Soldan, C, et al.
(författare)
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Synchrotron and collisional damping effects on runaway electron distributions
- 2016
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Ingår i: 58th Annual Meeting of the APS Division of Plasma Physics. ; 61:18, s. CO4.00010 -
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Validated models of runaway electron (RE) dissipation are required to confidently approve safe ITER Q=10 operation. DIII-D experiments using quiescent REs are exploring the importance of synchrotron and collisional damping terms to RE dissipation. New time and energy-resolved measurements of RE bremsstrahlung hard X-ray (HXR) emission reveal stark differences between high and low energy REs as damping terms are varied. Previously reported anomalously high RE dissipation only applies to low energy REs. At high energy (where synchrotron effects are strongest) low synchrotron damping cases reach higher peak RE energy despite weaker particle confinement. Low-energy RE decay is observed concurrently with high-energy RE growth. RE dissipation models predict bump-on-tail distributions whose properties depend on the damping terms. Measured HXR spectra are very broad, as expected for bump-on-tail distributions.
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| 4. |
- Wilkie, George, 1983, et al.
(författare)
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Fundamental form of the electrostatic δf-PIC algorithm and discovery of a converged numerical instability
- 2016
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:5, s. 052111-
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Tidskriftsartikel (refereegranskat)abstract
- The δf particle-in-cell algorithm has been a useful tool in studying the physics of plasmas, particularly turbulent magnetized plasmas in the context of gyrokinetics. The reduction in noise due to not having to resolve the full distribution function indicates an efficiency advantage over the standard (“full-f”) particle-in-cell. Despite its successes, the algorithm behaves strangely in some circumstances. In this work, we document a fully resolved numerical instability that occurs in the simplest of multiple-species test cases: the electrostatic ΩH mode. There is also a poorly understood numerical instability that occurs when one is under-resolved in particle number, which may require a prohibitively large number of particles to stabilize. Both of these are independent of the time-stepping scheme, and we conclude that they exist if the time advancement were exact. The exact analytic form of the algorithm is presented, and several schemes for mitigating these instabilities are also presented.
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| 5. |
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| 6. |
- Wilkie, George, 1983, et al.
(författare)
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Transport and deceleration of fusion products in microturbulence
- 2016
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:6, s. 060703-
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Tidskriftsartikel (refereegranskat)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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