| 1. |
- Meyer, H., et al.
(författare)
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Overview of physics results from MAST towards ITER/DEMO and the MAST Upgrade
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:10, s. 104008-
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Tidskriftsartikel (refereegranskat)abstract
- New diagnostic, modelling and plant capability on the Mega Ampere Spherical Tokamak (MAST) have delivered important results in key areas for ITER/DEMO and the upcoming MAST Upgrade, a step towards future ST devices on the path to fusion currently under procurement. Micro-stability analysis of the pedestal highlights the potential roles of micro-tearing modes and kinetic ballooning modes for the pedestal formation. Mitigation of edge localized modes (ELM) using resonant magnetic perturbation has been demonstrated for toroidal mode numbers n = 3, 4, 6 with an ELM frequency increase by up to a factor of 9, compatible with pellet fuelling. The peak heat flux of mitigated and natural ELMs follows the same linear trend with ELM energy loss and the first ELM-resolved T-i measurements in the divertor region are shown. Measurements of flow shear and turbulence dynamics during L-H transitions show filaments erupting from the plasma edge whilst the full flow shear is still present. Off-axis neutral beam injection helps to strongly reduce the redistribution of fast-ions due to fishbone modes when compared to on-axis injection. Low-k ion-scale turbulence has been measured in L-mode and compared to global gyro-kinetic simulations. A statistical analysis of principal turbulence time scales shows them to be of comparable magnitude and reasonably correlated with turbulence decorrelation time. T-e inside the island of a neoclassical tearing mode allow the analysis of the island evolution without assuming specific models for the heat flux. Other results include the discrepancy of the current profile evolution during the current ramp-up with solutions of the poloidal field diffusion equation, studies of the anomalous Doppler resonance compressional Alfven eigenmodes, disruption mitigation studies and modelling of the new divertor design for MAST Upgrade. The novel 3D electron Bernstein synthetic imaging shows promising first data sensitive to the edge current profile and flows.
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| 2. |
- Lloyd, B., et al.
(författare)
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Overview of physics results from MAST
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9, s. 094013 (paper no.)-
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Tidskriftsartikel (refereegranskat)abstract
- Major developments on the Mega Amp Spherical Tokamak (MAST) have enabled important advances in support of ITER and the physics basis of a spherical tokamak (ST) based component test facility (CTF), as well as providing new insight into underlying tokamak physics. For example, L-H transition studies benefit from high spatial and temporal resolution measurements of pedestal profile evolution (temperature, density and radial electric field) and in support of pedestal stability studies the edge current density profile has been inferred from motional Stark effect measurements. The influence of the q-profile and E x B flow shear on transport has been studied in MAST and equilibrium flow shear has been included in gyro-kinetic codes, improving comparisons with the experimental data. H-modes exhibit a weaker q and stronger collisionality dependence of heat diffusivity than implied by IPB98(gamma, 2) scaling, which may have important implications for the design of an ST-based CTF. ELM mitigation, an important issue for ITER, has been demonstrated by applying resonant magnetic perturbations (RMPs) using both internal and external coils, but full stabilization of type-I ELMs has not been observed. Modelling shows the importance of including the plasma response to the RMP fields. MAST plasmas with q > 1 and weak central magnetic shear regularly exhibit a long-lived saturated ideal internal mode. Measured plasma braking in the presence of this mode compares well with neo-classical toroidal viscosity theory. In support of basic physics understanding, high resolution Thomson scattering measurements are providing new insight into sawtooth crash dynamics and neo-classical tearing mode critical island widths. Retarding field analyser measurements show elevated ion temperatures in the scrape-off layer of L-mode plasmas and, in the presence of type-I ELMs, ions with energy greater than 500 eV are detected 20 cm outside the separatrix. Disruption mitigation by massive gas injection has reduced divertor heat loads by up to 70%.
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| 3. |
- Kirk, A., et al.
(författare)
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Magnetic perturbation experiments on MAST L and H-mode plasmas using internal coils
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 53, s. 065011-
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Tidskriftsartikel (refereegranskat)abstract
- Experiments have been performed on MAST using internal (n = 3) resonant magnetic perturbation (RMP) coils. The application of the RMPs to L-mode discharges has shown a clear density pump-out when the field line pitch angle at the low-field side of the plasma is sufficiently well aligned with the applied field. The application of the RMPs before the L–H transition increases the power required to achieve H-mode by at least 30%. In type I ELMing H-mode discharges, at a particular value of q95, the ELM frequency can be increased by a factor of 5 by the application of the RMPs. This effect on the ELMs and the L-mode density pump-out is not correlated with the width of the region for which the Chirikov parameter, calculated using the vacuum field, is greater than 1 but may be correlated with the size of the resonant component of the applied field in the pedestal region or with the location of the peak plasma displacement when the plasma response is taken into account.
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| 4. |
- Liang, Y., et al.
(författare)
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Mitigation of type-I ELMs with n=2 fields on JET with ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:7, s. 073036-
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Tidskriftsartikel (refereegranskat)abstract
- Mitigation of type-I edge-localized modes (ELMs) was observed with the application of an n = 2 field in H-mode plasmas on the JET tokamak with the ITER-like wall (ILW). Several new findings with the ILW were identified and contrasted to the previous carbon wall (C-wall) results for comparable conditions. Previous results for high collisionality plasmas (nu*(e,ped) similar to 2.0) with the C-wall saw little or no influence of either n = 1 or n = 2 fields on the ELMs. However, recent observations with the ILW show large type-I ELMs with a frequency of similar to 45 Hz were replaced by high-frequency (similar to 200 Hz) small ELMs during the application of the n = 2 field. With the ILW, splitting of the outer strike point was observed for the first time during the strong mitigation of the type-I ELMs. The maximal surface temperature (T-max) on the outer divertor plate reached a stationary state and has only small variations of a few degrees due to the small mitigated ELMs. In moderate collisionality (nu*(e,ped) similar to 0.8) H-mode plasmas, similar to previous results with the C-wall, both an increase in the ELM frequency and density pump-out were observed during the application of the n = 2 field. There are two new observations compared with the C-wall results. Firstly, the effect of ELM mitigation with the n = 2 field was seen to saturate so that the ELM frequency did not further increase above a certain level of n = 2 magnetic perturbations. Secondly splitting of the outer strike point during the ELM crash was seen, resulting in mitigation of the maximal ELM peak heat fluxes on the divertor region.
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| 5. |
- Liu, Yueqiang, 1971, et al.
(författare)
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Toroidal modelling of plasma response and RMP field penetration
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 54:12, s. 124013-
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Tidskriftsartikel (refereegranskat)abstract
- The penetration dynamics of the resonant magnetic perturbation (RMP) field is sim-ulated in the full toroidal geometry, under realistic plasma conditions in MAST experiments.The physics associated with several aspects of the RMP penetration - the plasma responseand rotational screening, the resonant and non-resonant torques and the toroidal momentumbalance - are highlighted. In particular, the plasma response is found to significantly amplifythe non-resonant component of the RMP field for some of the MAST plasmas. A fast rotatingplasma, in response to static external magnetic fields, experiences a more distributed electro-magnetic torque due to the resonance with continuum waves in the plasma. At fast plasmaflow (such as for the MAST plasma), the electromagnetic torque is normally dominant overthe neoclassical toroidal viscous (NTV) torque. However, at sufficiently slow plasma flow,the NTV torque can play a significant role in the toroidal momentum balance, thanks to theprecession drift resonance enhanced, so called superbanana plateau regime.
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