| 1. |
- Berger, Esmée, 1998, et al.
(författare)
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Runaway dynamics in reactor-scale spherical tokamak disruptions
- 2022
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 88:6
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Tidskriftsartikel (refereegranskat)abstract
- Understanding generation and mitigation of runaway electrons in disruptions is important for the safe operation of future tokamaks. In this paper we investigate the runaway dynamics in reactor-scale spherical tokamaks, focusing on a compact nominal design with a plasma current of 21 megaamperes (MA), 1.8 T magnetic field on axis and major radius of approximately 3 m. We study both the severity of runaway generation during unmitigated disruptions, and the effect that typical mitigation schemes based on massive material injection have on runaway production. The study is conducted using the numerical framework DREAM (Disruption Runaway Electron Analysis Model). We find that, in many cases, mitigation strategies are necessary to prevent the runaway current from reaching multi-MA levels. Our results indicate that, with a suitably chosen deuterium–neon mixture for mitigation, it is possible to achieve a tolerable runaway current and ohmic current evolution. However, this does not account for the runaway source due to wall activation, which has been found to severely limit successful mitigation at conventional aspect ratios, but whose definition requires a more complete wall specification. Furthermore, the majority of the thermal energy loss is found to happen through radial transport rather than radiation, which poses a risk of unacceptable localised heat loads.
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| 2. |
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| 3. |
- Buller, Stefan, 1991, et al.
(författare)
-
Neoclassical flows in deuterium-helium plasma density pedestals
- 2017
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 59:5, s. 055019-
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Tidskriftsartikel (refereegranskat)abstract
- In tokamak transport barriers, the radial scale of profile variations can be comparable to a typical ion orbit width, which makes the coupling of the distribution function across flux surfaces important in the collisional dynamics. We use the radially global steady-state neoclassical delta f code PERFECT [Landreman et al 2014 Plasma Phys. Control. Fusion 56 045005] to calculate poloidal and toroidal flows, and radial fluxes, in the pedestal. In particular, we have studied the changes in these quantities as the plasma composition is changed from a deuterium bulk species with a helium impurity to a helium bulk with a deuterium impurity, under specific profile similarity assumptions. In the presence of sharp profile variations, the poloidally resolved radial fluxes are important for the total fluxes to be divergence-free, which leads to the appearance of poloidal return-flows. These flows exhibit a complex radial–poloidal structure that extends several orbit widths into the core and is sensitive to abrupt radial changes in the ion temperature gradient. We find that a sizable neoclassical toroidal angular momentum transport can arise in the radially global theory, in contrast to the local.
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| 4. |
- Buller, Stefan, 1991, et al.
(författare)
-
Neoclassical study of the isotope effect in density pedestals
- 2017
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Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017. - 9781510849303 ; part 2, s. 841- 844
-
Konferensbidrag (refereegranskat)abstract
- The isotope mass scaling of the energy confinement time in tokamak plasmas typically differs from gyro-Bohm estimates. This phenomenon – known as the isotope effect – remains an open issue in plasma physics, with important implications for the extrapolation from present day, mostly deuterium (D), fusion experiments to future deuterium-tritium (D-T) reactors. Differences in mass scaling in L-mode and various H-mode regimes suggest that the isotope effect may, in large part, originate from the pedestal. In the pedestal, sharp gradients render local diffusive estimates invalid, and global effects due to orbit-width scale profile variations have to be taken into account, potentially leading to mass scalings different from gyro-Bohm. We calculate cross-field fluxes from a radially-global linearized drift-kinetic equation using the PERFECT code, to study isotope composition effects in density pedestals. We define dimensionless parameters from the ratios of density length scale, pedestal width and orbit width, and study global effects in terms of these parameters for different pedestal profiles and bulk species. Quantifying global effects by the relative difference between peak heat-flux values in global and local simulations, we find that this quantity saturates at an isotope-dependent value, but the dimensionless parameters do not capture all the isotope dependencies. We also consider D-T and H-D mixtures, and compare the calculated heat fluxes to fluxes calculated from single species simulations with artificial "DT" and "HD" species.
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| 5. |
- Buller, Stefan, 1991, et al.
(författare)
-
Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 59:6
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Tidskriftsartikel (refereegranskat)abstract
- Avoiding impurity accumulation is a requirement for steady-state stellarator operation. The accumulation of impurities can be heavily affected by variations in their density on the flux-surface. Using recently derived semi-analytic expressions for the transport of a collisional impurity species with high-Z and flux-surface density-variation in the presence of a low-collisionality bulk ion species, we numerically optimize the impurity density-variation on the flux-surface to minimize the radial peaking factor of the impurities. These optimized density-variations can reduce the core impurity density by 0.75^Z (with Z the impurity charge number) in the large helical device case considered here, and by 0.89^Z in a Wendelstein 7-X standard configuration case. On the other hand, when the same procedure is used to find density-variations that maximize the peaking factor, it is notably increased compared to the case with no density-variation. This highlights the potential importance of measuring and controlling these variations in experiments.
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| 6. |
- Embréus, Ola, 1991, et al.
(författare)
-
Numerical calculation of ion runaway distributions
- 2015
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Ingår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015.
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Konferensbidrag (refereegranskat)abstract
- Numerical solver of the 2D ion Fokker-Planck equation has been presented, and its usefulness demonstrated in investigating the conditions required for ion runaway in cold and hot tokamak plasmas. It is shown that Alfvénic activity observed in disruption experiments are unlikely to be explained by the runaway mechanism alone.
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| 7. |
- Embréus, Ola, 1991, et al.
(författare)
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Numerical calculation of ion runaway distributions
- 2015
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 22:5, s. 052122-
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Tidskriftsartikel (refereegranskat)abstract
- Ions accelerated by electric fields (so-called runaway ions) in plasmas may explain observations in solar flares and fusion experiments; however, limitations of previous analytic work have prevented definite conclusions. In this work, we describe a numerical solver of the 2D non-relativistic linearized Fokker-Planck equation for ions. It solves the initial value problem in velocity space with a spectral-Eulerian discretization scheme, allowing arbitrary plasma composition and time-varying electric fields and background plasma parameters. The numerical ion distribution function is then used to consider the conditions for runaway ion acceleration in solar flares and tokamak plasmas. Typical time scales and electric fields required for ion acceleration are determined for various plasma compositions, ion species, and temperatures, and the potential for excitation of toroidal Alfvén eigenmodes during tokamak disruptions is considered.
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| 8. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Alfvénic instabilities driven by runaways in fusion plasmas
- 2014
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 21:8, s. 080702-
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Tidskriftsartikel (refereegranskat)abstract
- Runaway particles can be produced in plasmas with large electric fields. Here, we address the possibility that such runaway ions and electrons excite Alfvénic instabilities. The magnetic perturbation induced by these modes can enhance the loss of runaways. This may have important implications for the runaway electron beam formation in tokamak disruptions.
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| 9. |
- 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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| 10. |
- Harrison, J.R., et al.
(författare)
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Overview of new MAST physics in anticipation of first results from MAST Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 ∼ 1.3) with similar poloidal cross-section to other medium-size tokamaks. The physics programme concentrates on addressing key physics issues for the operation of ITER, design of DEMO and future spherical tokamaks by utilising high resolution diagnostic measurements closely coupled with theory and modelling to significantly advance our understanding. An empirical scaling of the energy confinement time that favours higher power, lower collisionality devices is consistent with gyrokinetic modelling of electron scale turbulence. Measurements of ion scale turbulence with beam emission spectroscopy and gyrokinetic modelling in up-down symmetric plasmas find that the symmetry of the turbulence is broken by flow shear. Near the non-linear stability threshold, flow shear tilts the density fluctuation correlation function and skews the fluctuation amplitude distribution. Results from fast particle physics studies include the observation that sawteeth are found to redistribute passing and trapped fast particles injected from neutral beam injectors in equal measure, suggesting that resonances between the m = 1 perturbation and the fast ion orbits may be playing a dominant role in the fast ion transport. Measured D-D fusion products from a neutron camera and a charged fusion product detector are 40% lower than predictions from TRANSP/NUBEAM, highlighting possible deficiencies in the guiding centre approximation. Modelling of fast ion losses in the presence of resonant magnetic perturbations (RMPs) can reproduce trends observed in experiments when the plasma response and charge-exchange losses are accounted for. Measurements with a neutral particle analyser during merging-compression start-up indicate the acceleration of ions and electrons. Transport at the plasma edge has been improved through reciprocating probe measurements that have characterised a geodesic acoustic mode at the edge of an ohmic L-mode plasma and particle-in-cell modelling has improved the interpretation of plasma potential estimates from ball-pen probes. The application of RMPs leads to a reduction in particle confinement in L-mode and H-mode and an increase in the core ionization source. The ejection of secondary filaments following type-I ELMs correlates with interactions with surfaces near the X-point. Simulations of the interaction between pairs of filaments in the scrape-off layer suggest this results in modest changes to their velocity, and in most cases can be treated as moving independently. A stochastic model of scrape-off layer profile formation based on the superposition of non-interacting filaments is in good agreement with measured time-average profiles. Transport in the divertor has been improved through fast camera imaging, indicating the presence of a quiescent region devoid of filament near the X-point, extending from the separatrix to ψ n ∼ 1.02. Simulations of turbulent transport in the divertor show that the angle between the divertor leg on the curvature vector strongly influences transport into the private flux region via the interchange mechanism. Coherence imaging measurements show counter-streaming flows of impurities due to gas puffing increasing the pressure on field lines where the gas is ionised. MAST Upgrade is based on the original MAST device, with substantially improved capabilities to operate with a Super-X divertor to test extended divertor leg concepts. SOLPS-ITER modelling predicts the detachment threshold will be reduced by more than a factor of 2, in terms of upstream density, in the Super-X compared with a conventional configuration and that the radiation front movement is passively stabilised before it reaches the X-point. 1D fluid modelling reveals the key role of momentum and power loss mechanisms in governing detachment onset and evolution. Analytic modelling indicates that long legs placed at large major radius, or equivalently low at the target compared with the X-point are more amenable to external control. With MAST Upgrade experiments expected in 2019, a thorough characterisation of the sources of the intrinsic error field has been carried out and a mitigation strategy developed.
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| 11. |
- Helander, P., et al.
(författare)
-
Impurity Transport in a Mixed-Collisionality Stellarator Plasma
- 2017
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:15, s. 155002 -
-
Tidskriftsartikel (refereegranskat)abstract
- A potential threat to the performance of magnetically confined fusion plasmas is the problem of impurity accumulation, which causes the concentration of highly charged impurity ions to rise uncontrollably in the center of the plasma and spoil the energy confinement by excessive radiation. It has long been thought that the collisional transport of impurities in stellarators always leads to such an accumulation (if the electric field points inwards, which is usually the case), whereas tokamaks, being axisymmetric, can benefit from "temperature screening," i.e., an outward flux of impurities driven by the temperature gradient. Here it is shown, using analytical techniques supported by results from a new numerical code, that such screening can arise in stellarator plasmas, too, and indeed does so in one of the most relevant operating regimes, where the impurities are highly collisional while the bulk plasma is at low collisionality.
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| 12. |
- Helander, Per, 1967, et al.
(författare)
-
Stellarator bootstrap current and plasma flow velocity at low collisionality
- 2017
-
Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 83:2
-
Tidskriftsartikel (refereegranskat)abstract
- The bootstrap current and flow velocity of a low-collisionality stellarator plasma are calculated. As far as possible, the analysis is carried out in a uniform way across all low-collisionality regimes in general stellarator geometry, assuming only that the confinement is good enough that the plasma is approximately in local thermodynamic equilibrium. It is found that conventional expressions for the ion flow speed and bootstrap current in the low-collisionality limit are accurate only in the 1/nu -collisionality regime and need to be modified in the root-nu-regime. The correction due to finite collisionality is also discussed and is found to scale as nu^2/5
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| 13. |
- Hesslow, Linnea, 1993, et al.
(författare)
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Effect of partially-screened nuclei on fast-electron dynamics
- 2017
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:25, s. article no. 5501-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms, where the screening effect of bound electrons must be included. We derive analytical expressions for the deflection and slowing-down frequencies, and show that they are increased significantly compared to the results obtained with complete screening, already at sub-relativistic electron energies. Furthermore, we show that the modifications to the deflection and slowing down frequencies are of equal importance in describing the runaway current evolution. Our results greatly affect fast-electron dynamics and have important implications, e.g. for the efficacy of mitigation strategies for runaway electrons in tokamak devices, and energy loss during relativistic breakdown in atmospheric discharges.
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| 14. |
- Hesslow, Linnea, 1993, et al.
(författare)
-
Kinetic effects of partially screened impurities in runaway-electron mitigation scenarios
- 2017
-
Ingår i: International Sherwood Fusion Theory Conference, Annapolis, USA.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Runaway electrons constitute a significant threat to tokamak devices. Their mitigation by heavy-impurity injection has been experimentally shown to be more effective than would be expected from standard collisional theory [1]. In order to understand this effect and develop runaway mitigation schemes, more accurate kinetic models are needed to describe the interaction between electrons and partially ionized atoms. Such models require the partial screening of the nuclei by the bound electrons to be taken into account.In this contribution, we analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms. A generalized collision operator is derived from first principles using quantum-mechanical models. We obtain analytical expressions for the deflection and slowing-down frequencies. Even at sub-relativistic energies, these are increased by more than an order of magnitude compared to the results obtained with complete screening. Moreover, we implement the generalized collision operator in the continuum kinetic-equation solver CODE [2, 3] and demonstrate that interaction with partially ionized atoms greatly affects fast-electron dynamics by enhancing the rates of angular deflection and energy loss. In particular, we investigate the decay of a runaway-electron current coupled to a self-consistent electric field. The effect of the interaction with partially ionized impurities has important implications for the efficacy of mitigation strategies for runaway electrons in tokamak devices.References[1] E. M. Hollmann et al., Physics of Plasmas 22, 056108 (2015).[2] M. Landreman, A. Stahl and T. Fülöp, Comp. Phys. Comm. 185, 847 (2014).[3] A. Stahl et al., Nuclear Fusion 56, 112009 (2016).
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| 15. |
- Labit, B., et al.
(författare)
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Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:8
-
Tidskriftsartikel (refereegranskat)abstract
- © 2019 Institute of Physics Publishing. All rights reserved. Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (ne,sep/nG ∼ 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.
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| 16. |
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| 17. |
- Newton, Sarah, 1981, et al.
(författare)
-
Impurity transport and bulk ion flow in a mixed collisionality stellarator plasma
- 2017
-
Ingår i: Journal of Plasma Physics. - : Cambridge University Press (CUP). - 0022-3778 .- 1469-7807. ; 83:5
-
Tidskriftsartikel (refereegranskat)abstract
- The accumulation of impurities in the core of magnetically confined plasmas, resulting from standard collisional transport mechanisms, is a known threat to their performance as fusion energy sources. Whilst the axisymmetric tokamak systems have been shown to benefit from the effect of temperature screening, that is an outward flux of impurities driven by the temperature gradient, impurity accumulation in stellarators was thought to be inevitable, driven robustly by the inward pointing electric field characteristic of hot fusion plasmas. We have shown in Helander et al. (Phys. Rev. Lett, vol. 118, 2017a, 155002) that such screening can in principle also appear in stellarators, in the experimentally relevant mixed collisionality regime, where a highly collisional impurity species is present in a low collisionality bulk plasma. Details of the analytic calculation are presented here, along with the effect of the impurity on the bulk ion flow, which will ultimately affect the bulk contribution to the bootstrap current.
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| 18. |
- Newton, Sarah, 1981, et al.
(författare)
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Impurity transport and plasma flow in a mixed collisionality stellarator plasma
- 2016
-
Ingår i: Proceedings of 26th IAEA Fusion Energy Conference, Kyoto, Japan. ; , s. THC/PDP-15
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Neoclassical accumulation of impurities in the core of hot stellarator plasmas is a known problem. The complexity of neoclassical transport in stellarators means that few analytic studies are available to support numerical modelling efforts, and a robust understanding of the parameter dependence of the impurity flux is still lacking.Therefore we present an extension of the existing analytic treatment for highly collisional plasmas, into the experimentally relevant mixed collisionality regime -- where a dominant heavy, collisional, impurity is present in a collisionless bulk plasma, taken here to be in the 1/\nu regime.We find that temperature screening of the impurity flux by the bulk ion temperature gradient will arise.We also determine the bulk ion flow in the flux surface, and thus the effect of the impurity on the bulk ion contribution to the bootstrap current.
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| 19. |
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| 20. |
- Newton, Sarah, 1981, et al.
(författare)
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Numerical calculation of ion runaway distributions
- 2015
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Ingår i: 57th Annual Meeting of the APS Division of Plasma Physics. ; 60:19, s. CP12.00118-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ion acceleration by electric fields is of interest in many plasma scenarios. Limitations of analytic descriptions prevent their general use in following the evolution of such ``runaway ion'' populations. Therefore we have implemented an initial value solver, CODION, for the linearized ion drift kinetic equation, with a non-relativistic Fokker-Planck collision operator. A spectral-Eulerian discretization scheme is used for 2D velocity space. The background plasma is taken to be homogeneous and static, with arbitrary composition. We demonstrate the use of the numerical distribution function to study ion acceleration in solar flares and tokamak plasmas. The variation of the strength and duration of the electric field required to produce a significant fast ion population is illustrated. Low frequency magnetic activity, indicative of toroidal Alfv\'{e}n eigenmode excitation, has been observed during tokamak disruptions. Taking typical disruption parameters, we show that accelerated bulk ions are unlikely to reach a sufficient velocity to provide the resonant drive.
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| 21. |
- Omotani, John, 1985, et al.
(författare)
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Edge momentum transport by neutrals
- 2016
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Ingår i: Proceedings of 26th IAEA Fusion Energy Conference, Kyoto, Japan. ; , s. TH/P3-18
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to their high cross-field mobility, neutrals can contribute to momentum transport evenat the low relative densities found inside the separatrix and they can generate intrinsicrotation. We use a charge-exchange dominated solution to the neutral kinetic equation,coupled to neoclassical ions, to evaluate the momentum transport due to neutrals. Numer-ical solutions to the drift-kinetic equation allow us to model the intermediate collisionalitytypical of the tokamak edge. In the edge there are several processes likely to contribute tomomentum transport in addition to neutrals. Therefore, we present here an interpretativeframework that can evaluate the momentum transport through neutrals based on radialplasma profiles. We demonstrate its application with representative artificial profiles andan analytical equilibrium, with parameters typical of L-mode in a medium-sized tokamak.The magnitudes of the torques we find here due to neutrals are 0.5–5 N·m, motivating theapplication of our framework to experimental data, where it will allow us to evaluate theimportance of the momentum flux due to neutrals compared to other transport mechanisms.
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| 22. |
- Omotani, John, 1985, et al.
(författare)
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Edge momentum transport by neutrals: an interpretive numerical framework
- 2017
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 57:6, s. 066048-
-
Tidskriftsartikel (refereegranskat)abstract
- Due to their high cross-field mobility, neutrals can contribute to momentum transport even at the low relative densities found inside the separatrix and they can generate intrinsic rotation. We use a charge-exchange dominated solution to the neutral kinetic equation, coupled to neoclassical ions, to evaluate the momentum transport due to neutrals. Numerical solutions to the drift-kinetic equation allow us to cover the full range of collisionality, including the intermediate levels typical of the tokamak edge. In the edge there are several processes likely to contribute to momentum transport in addition to neutrals. Therefore, we present here an interpretive framework that can evaluate the momentum transport through neutrals based on radial plasma profiles. We demonstrate its application by analysing the neutral angular momentum flux for an L-mode discharge in the ASDEX Upgrade tokamak. The magnitudes of the angular momentum fluxes we find here due to neutrals of 0.6–2 N m are comparable to the net torque on the plasma from neutral beam injection, indicating the importance of neutrals for rotation in the edge.
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| 23. |
- Omotani, John, 1985, et al.
(författare)
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Edge rotation from momentum transport by neutrals
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 775:1
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Konferensbidrag (refereegranskat)abstract
- Due to their high cross field mobility, neutral atoms can have a strong effect on transporteven at the low relative densities found inside the separatrix. We use a charge-exchange dominatedmodel for the neutrals, coupled to neoclassical ions, to calculate momentum transport when it isdominated by the neutrals. We can then calculate self-consistently the radial electric field and predictthe intrinsic rotation in a torque-free plasma. Using a numerical solver for the ion distribution toallow arbitrary collisionality, we investigate the effects of inverse aspect ratio and elongation on plasmarotation. We also calculate the rotation of a trace carbon impurity, to facilitate future comparison toexperiments using charge exchange recombination spectroscopy diagnostics.
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| 24. |
- Omotani, John, 1985, et al.
(författare)
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Momentum transport by neutrals: Effect of kinetic coupling
- 2017
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Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017.
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Konferensbidrag (refereegranskat)abstract
- Neutrals couple to the non-Maxwellian as well as (drifting-)Maxwellian parts of the ion distribution function, producing a residual stress that can drive intrinsic rotation. Our modelling predicted a steeper slope of the toroidal rotation profile than observed in dedicated AUG discharges, suggesting the presence of opposing transport mechanisms. Losses from neutrals escaping to the wall which are not captured by the short MFP approximation, neoclassical torque from the toroidal ripple field or turbulent transport are all possibilities. Finally, we did not predict or observe a significant change in the measured rotation profiles when changing the gas fuelling location. This may be due to the modest fuelling possible in the low density discharges used.
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| 25. |
- Omotani, John, 1985, et al.
(författare)
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Plasma rotation from momentum transport by neutrals in tokamaks
- 2016
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 56:12, s. 124002-
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Tidskriftsartikel (refereegranskat)abstract
- Neutral atoms can strongly influence the intrinsic rotation and radial electric field at the tokamak edge. Here, we present a framework to investigate these effects when the neutrals dominate the momentum transport. We explore the parameter space numerically, using highly flexible model geometries and a state of the art kinetic solver. We find that the most important parameters controlling the toroidal rotation and electric field are the major radius where the neutrals are localized and the plasma collisionality. This offers a means to influence the rotation and electric field by, for example, varying the radial position of the X-point to change the major radius of the neutral peak.
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