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| 2. |
- Martin, P., et al.
(author)
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Overview of the RFX fusion science program
- 2011
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In: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 51:9, s. 094023-
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Journal article (peer-reviewed)abstract
- This paper summarizes the main achievements of the RFX fusion science program in the period between the 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is the largest reversed field pinch in the world, equipped with a system of 192 coils for active control of MHD stability. The discovery and understanding of helical states with electron internal transport barriers and core electron temperature >1.5 keV significantly advances the perspectives of the configuration. Optimized experiments with plasma current up to 1.8 MA have been realized, confirming positive scaling. The first evidence of edge transport barriers is presented. Progress has been made also in the control of first-wall properties and of density profiles, with initial first-wall lithization experiments. Micro-turbulence mechanisms such as ion temperature gradient and micro-tearing are discussed in the framework of understanding gradient-driven transport in low magnetic chaos helical regimes. Both tearing mode and resistive wall mode active control have been optimized and experimental data have been used to benchmark numerical codes. The RFX programme also provides important results for the fusion community and in particular for tokamaks and stellarators on feedback control of MHD stability and on three-dimensional physics. On the latter topic, the result of the application of stellarator codes to describe three-dimensional reversed field pinch physics will be presented.
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| 3. |
- Terranova, D., et al.
(author)
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A 3D approach to equilibrium, stability and transport studies in RFX-mod improved regimes
- 2010
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 52:12, s. 124023-
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Journal article (peer-reviewed)abstract
- The full three-dimensional (3D) approach is now becoming an important issue for all magnetic confinement configurations. It is a necessary condition for the stellarator but also the tokamak and the reversed field pinch (RFP) now cannot be completely described in an axisymmetric framework. For the RFP the observation of self-sustained helical configurations with improved plasma performances require a better description in order to assess a new view on this configuration. In this new framework plasma configuration studies for RFX-mod have been considered both with tools developed for the RFP as well as considering codes originally developed for the stellarator and adapted to the RFP. These helical states are reached through a transition to a very low/reversed shear configuration leading to internal electron transport barriers. These states are interrupted by MHD reconnection events and the large Te gradients at the barriers indicate that both current and pressure driven modes are to be considered. Furthermore the typically flat Te profiles in the helical core have raised the issue of the role of electrostatic and electromagnetic turbulence in these reduced chaos regions, so that a stability analysis in the correct 3D geometry is required to address an optimization of the plasma setup. In this viewtheVMECcode proved to be an effectiveway to obtain helical equilibria to be studied in terms of stability and transport with a suite of well tested codes. In this work, the equilibrium reconstruction technique as well as the experimental evidence of 3D effects and their first interpretation in terms of stability and transport are presented using both RFP and stellarator tools.
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| 4. |
- Papp, Gergely, 1985, et al.
(author)
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Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas
- 2015
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In: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 81:3, s. 475810503-
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Journal article (peer-reviewed)abstract
- The transport of energetic electrons is sensitive to magnetic perturbations. By using 3D numerical simulation of test particle drift orbits we show that the transport of untrapped electrons through an open region with magnetic perturbations cannot be described by a diffusive process. Based on our test particle simulations, we propose a model that leads to an exponential loss of particles.
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| 5. |
- Papp, Gergely, 1985, et al.
(author)
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Runaway electron dynamics and transport anisotropy due to resonant magnetic perturbations in ITER
- 2012
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In: Proceedings of the 24th IAEA Fusion Energy Conference. ; , s. TH/P4-05
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Conference paper (peer-reviewed)abstract
- In this paper the effect of resonant magnetic perturbations (RMP) on the net radial transport of runaway electrons (RE) is calculated by simulating the RE drift orbits in magnetostatic perturbed fields. Through the transport, RMP influences the time dynamics andpreferred loss directions of the REs. The distribution of the field mesh exit points of therunaway electrons become more localised compared to the unperturbed case, since the losspattern depends on the geometric properties of the RMP configuration such as periodicityor helicity. On the other hand, the loss patterns do not depend on the particle energiesand starting positions. The particle radial steps are correlated to the local radial magneticperturbation component, which makes the transport chaotic, but deterministic.
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| 6. |
- Papp, Gergely, 1985, et al.
(author)
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Runaway electron losses enhanced by resonant magnetic perturbations
- 2011
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In: Proceedings of 12th Technical Meeting on Energetic Particles in Magnetic Confinement Systems. ; , s. O.26-
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Conference paper (peer-reviewed)abstract
- Disruptions in large tokamaks can lead to the generation of a relativistic runaway electronbeam that may cause serious damage to the first wall. To suppress the runaway beam the applicationof resonant magnetic perturbations (RMP) has been suggested. In this work we investigate the effect ofresonant magnetic perturbations on the confinement of runaway electrons by simulating their drift orbitsin magnetostatic perturbed fields and calculating the transport and orbit losses for various initial energiesand different magnetic perturbation configurations. In the simulations we use model configurations withexisting (TEXTOR) and planned (ITER) RMP systems, and solve the relativistic, gyro-averaged driftequations for the runaway electrons including the electric field, radiation losses and collisions. The resultsindicate that runaway electrons are well confined in the core of the device, but the onset time of runawaylosses closer to the edge is dependent on the magnetic perturbation level, which can thereby affectthe maximum runaway current. Runaway electrons are rapidly lost from regions where the normalisedperturbation amplitude \delta B/B is larger than 0.1% in a properly chosen perturbation geometry. Thisapplies to the region outside the radius corresponding to the normalised flux \psi = 0.5 in ITER, when theELM mitigation coils are used at maximum current in their most favourable configuration.
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| 7. |
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| 8. |
- Papp, Gergely, 1985, et al.
(author)
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The effect of magnetic perturbations on runaway dynamics
- 2013
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In: Proceeding of the13th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems. ; , s. IAEA-F1-TM-44766 / I12-
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Conference paper (peer-reviewed)abstract
- Disruptions in large tokamaks can lead to the generation of a relativistic runaway (RE) electron beam that may cause serious damage to the first wall. To suppress the RE beamthe application of resonant magnetic perturbations (RMP) has been suggested. We investigate the effect of resonant magnetic perturbations by simulating the RE drift orbits inmagnetostatic perturbed fields and calculating the transport and orbit losses for various particle energies and different magnetic perturbation configurations. In the simulations we use model configurations with the planned ITER RMP system and solve the relativistic, gyro-averaged drift equations for the runaway electrons including radiation losses and collisions. The results indicate that runaway electrons are rapidly lost from regions where thenormalised perturbation amplitude δB/B is larger than ∼0.1% in a properly chosen perturbation geometry. This corresponds to the outer half of the confinement volume in ITER. We show that despite the chaotic magnetic topology the ensemble behaviour can only be approximated by a diffusion process.
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| 9. |
- Papp, Gergely, 1985, et al.
(author)
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The effect of resonant magnetic perturbations on runaway electron transport in ITER
- 2012
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 54:12, s. 125008-
-
Journal article (peer-reviewed)abstract
- In this paper the effect of resonant magnetic perturbations (RMPs) on the net radial transport of runaway electrons (REs) is calculated by simulating the RE drift orbits in magnetostatic perturbed fields. Through the transport, RMP influences the time dynamics and preferred loss directions of the REs, which are determined for different magnetic perturbation configurations. The distribution of the field mesh exit points of the REs become more localized compared with the unperturbed case, since the loss pattern depends on the geometric properties of the RMP configuration such as periodicity or helicity. On the other hand, the loss patterns do not depend on the particle energies and starting positions. The particle radial steps are correlated with the local radial magnetic perturbation component, which makes the transport chaotic, but deterministic.
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| 10. |
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