| 1. |
- Bombarda, F., et al.
(författare)
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Runaway electron beam control
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Cecconello, Marco, et al.
(författare)
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Energetic ion behaviour in MAST
- 2015
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 57:1, s. 014006-
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies of fast ion transport resulting from a range of instabilities, including n = 1 internal kink modes (fishbones and long-lived modes), toroidal Alfven eigenmodes and sawteeth have been carried out at MAST. Strong correlations were found between relative changes in magnetic edge coils signals, edge D alpha signal a fast ion D alpha system, a prototype collimated neutron flux monitor and a recently installed prototype charged fusion product detector array, indicating both redistribution and loss of fast ions. Preliminary interpretation of these observations with a suite of stability, modelling and interpretative codes is discussed.
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| 3. |
- Cecconello, Marco, et al.
(författare)
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Impurity transport driven by fishbones in MAST
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:3
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Tidskriftsartikel (refereegranskat)abstract
- In MAST, bursting toroidal Alfven eigenmodes and fishbones are observed to give rise to an asymmetric perturbation to the soft x-ray (SXR) emission close to the magnetic axis which grows and decays on the time scale of the fishbone evolution. As the fishbone nears its maximum amplitude, the SXR emission starts to increase (decrease) at radial positions smaller (larger) than the radial position of the magnetic axis. This trend in the SXR emission persists for a few milliseconds, until the fishbone starts to decay in amplitude and the slower overall trend of the SXR emission once again becomes dominant. A preliminary analysis suggests that the change in the SXR emission is due to the localized accumulation of high-Z impurities, sustained against parallel transport by the effects of fishbones on the fast ion population.
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| 4. |
- Dendy, R.O., et al.
(författare)
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Energetic particles in magnetic confinement systems : Synergies beyond fusion
- 2002
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic confinement fusion science leads many other branches of plasma physics in its capacity to predict, interpret and understand the behaviour of energetic particle populations. The range of applications of this capability should be extended, for the mutual benefit of fusion research and of other branches of science. In this paper we review progress in applying fusion-derived techniques to one of the central questions of astrophysics: the origin of the cosmic ray population that is magnetically confined within our Galaxy. While it is widely believed that supernova remnant shocks provide the main acceleration sites for cosmic ray electrons and protons, the fundamental 'injection' problem remains. Namely, how particles are initially accelerated from ambient thermal to mildly relativistic energies, beyond which Fermi-type processes take over. The cosmic ray injection environment is magnetized and has many other physical resemblances to beam-heated and deuterium-tritium tokamak plasmas, in consequence, many of the same physical processes come into play. These include, for example, collective beam-plasma instability, resonant wave-particle coupling, and the stochasticization of particle orbits. A broad range of analytical and numerical techniques familiar in the fusion context has been successfully applied to the injection problem (see, for example, Dieckmann M.E. et al 2000 Astron. Astrophys. 356 377). Ideas from magnetic fusion have also been used to help design and interpret recent magnetized plasma experiments (Woolsey N.C. et al 2001 Phys. Plasmas 8 2439) using the high-power VULCAN laser, which address the cosmic ray injection problem from a new perspective.
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| 5. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Three-dimensional visualization of electron acceleration in a magnetized plasma
- 2002
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 30:1 I, s. 20-21
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Tidskriftsartikel (refereegranskat)abstract
- We examine wave-particle interactions in a magnetized plasma. We present snapshots of an animation of the three-dimensional electron phase space distribution produced by an electrostatic wave propagating across a magnetic field. The distribution function has been evolved by a particle in cell simulation. The electron phase space has been visualized by distributing the simulation electrons over an array representing phase space density and by volume rendering this array. The results are, due to the choice of initial plasma and wave parameters, of relevance for electron acceleration at astrophysical shocks.
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| 6. |
- Hobirk, J., et al.
(författare)
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The JET hybrid scenario in Deuterium, Tritium and Deuterium-Tritium
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 63:11
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Tidskriftsartikel (refereegranskat)abstract
- The JET hybrid scenario has been developed from low plasma current carbon wall discharges to the record-breaking Deuterium-Tritium plasmas obtained in 2021 with the ITER-like Be/W wall. The development started in pure Deuterium with refinement of the plasma current, and toroidal magnetic field choices and succeeded in solving the heat load challenges arising from 37 MW of injected power in the ITER like wall environment, keeping the radiation in the edge and core controlled, avoiding MHD instabilities and reaching high neutron rates. The Deuterium hybrid plasmas have been re-run in Tritium and methods have been found to keep the radiation controlled but not at high fusion performance probably due to time constraints. For the first time this scenario has been run in Deuterium-Tritium (50:50). These plasmas were re-optimised to have a radiation-stable H-mode entry phase, good impurity control through edge Ti gradient screening and optimised performance with fusion power exceeding 10 MW for longer than three alpha particle slow down times, 8.3 MW averaged over 5 s and fusion energy of 45.8 MJ.
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| 7. |
- Jackson, A. R., et al.
(författare)
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Diagnosing fast ion redistribution due to sawtooth instabilities using fast ion deuterium-alpha spectroscopy in the mega amp spherical tokamak
- 2020
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 60:12
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Tidskriftsartikel (refereegranskat)abstract
- A comparison between fast ion measurements and sawtooth models in the Mega Amp Spherical Tokamak (MAST) is extended to include fast ion deuterium-alpha (FIDA) data. It is concluded that FIDA data cannot be used to distinguish between three alternative models used in the plasma transport/fast particle code TRANSP/NUBEAM to simulate fast ion redistribution during sawteeth. For FIDA lines-of-sight that probe the sawtoothing region, at each sawtooth crash there is an overall drop in the emission of up to 60%. Data from passive FIDA lines-of-sight (i.e.with emission resulting from neutralisation by thermal neutrals in the plasma periphery rather than beam neutrals) show a sudden increase in the emission following sawtooth crashes. The subsequent decay in the emission in these passive channels indicates that redistributed passing fast ions are rapidly lost from the edge region, probably as a result of charge-exchange reactions with edge neutrals.
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| 8. |
- Jones, O. M., et al.
(författare)
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Measurements and modelling of fast-ion redistribution due to resonant MHD instabilities in MAST
- 2015
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 57:12
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Tidskriftsartikel (refereegranskat)abstract
- The results of a comprehensive investigation into the effects of toroidicity-induced Alfven eigenmodes (TAE) and energetic particle modes on the NBI-generated fast-ion population in MAST plasmas are reported. Fast-ion redistribution due to frequency-chirping TAE in the range 50 kHz-100 kHz and frequency-chirping energetic particle modes known as fishbones in the range 20 kHz-50 kHz, is observed. TAE and fishbones are also observed to cause losses of fast ions from the plasma. The spatial and temporal evolution of the fast-ion distribution is determined using a fission chamber, a radially-scanning collimated neutron flux monitor, a fast-ion deuterium alpha spectrometer and a charged fusion product detector. Modelling using the global transport analysis code TRANSP, with ad hoc anomalous diffusion and fishbone loss models introduced, reproduces the coarsest features of the affected fast-ion distribution in the presence of energetic particle-driven modes. The spectrally and spatially resolved measurements show, however, that these models do not fully capture the effects of chirping modes on the fast-ion distribution.
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| 9. |
- Keeling, D. L., et al.
(författare)
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Mitigation of MHD induced fast-ion redistribution in MAST and implications for MAST-Upgrade design
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:1
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of the redistribution of neutral beam fast ions due to magnetohydrodynamic (MHD) activity in plasma has been observed on many tokamaks and more recently has been a focus of research on MAST (Turnyanskiy et al 2013 Nucl. Fusion 53 053016). n = 1 fishbone modes are observed to cause a large decrease in the neutron emission rate indicating the existence of a significant perturbation of the fast-ion population in the plasma. Theoretical work on fishbone modes states that the fast-ion distribution itself acts as the source of free energy driving the modes that cause the redistribution. Therefore a series of experiments have been carried out on MAST to investigate a range of plasma densities at two neutral-beam power levels to determine the region within this parameter space in which fishbone activity and consequent fast-ion redistribution is suppressed. Analysis of these experiments shows complete suppression of fishbone activity at high densities with increasing activity and fast-ion redistribution at lower densities and higher neutral-beam power, accompanied by strong evidence that the redistribution effect primarily affects a specific region in the plasma core with a weaker effect over a wider region of the plasma. The results also indicate the existence of correlations between gradients in the modelled fast-ion distribution function, the amplitude and growth rate of the fishbone modes, and the magnitude of the redistribution effect. The same analysis has been carried out on models of MAST-Upgrade baseline plasma scenarios to determine whether significant fast-ion redistribution due to fishbone modes is likely to occur in that device. A simple change to the neutral-beam injector geometry is proposed which is shown to have a significant mitigating effect in terms of the fishbone mode drive and is therefore expected to allow effective plasma heating and current drive over a wider range of plasma conditions in MAST-Upgrade.
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| 10. |
- Knight, P.J., et al.
(författare)
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CENTORI: A global toroidal electromagnetic two-fluid plasma turbulence code
- 2012
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 183:11, s. 2346-2363
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Tidskriftsartikel (refereegranskat)abstract
- A new global two-fluid electromagnetic turbulence code, CENTORI, has been developed for the purpose of studying magnetically-confined fusion plasmas on energy confinement timescales. This code is used to evolve the combined system of electron and ion fluid equations and Maxwell equations in toroidal configurations with axisymmetric equilibria. Uniquely, the equilibrium is co-evolved with the turbulence, and is thus modified by it. CENTORI is applicable to tokamaks of arbitrary aspect ratio and high plasma beta. A predictor–corrector, semi-implicit finite difference scheme is used to compute the time evolution of fluid quantities and fields. Vector operations and the evaluation of flux surface averages are speeded up by choosing the Jacobian of the transformation from laboratory to plasma coordinates to be a function of the equilibrium poloidal magnetic flux. A subroutine, GRASS, is used to co-evolve the plasma equilibrium by computing the steady-state solutions of a diffusion equation with a pseudo-time derivative. The code is written in Fortran 95 and is efficiently parallelised using Message Passing Interface (MPI). Illustrative examples of output from simulations of a tearing mode in a large aspect ratio tokamak plasma and of turbulence in an elongated conventional aspect ratio tokamak plasma are provided.
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