| 1. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 2. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 3. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 4. |
- Lönnroth, J. -S, et al.
(författare)
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Integrated ELM modelling
- 2006
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 46:7-9, s. 726-738
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a short overview of current trends and progress in integrated ELM modelling. First, the concept of integrated ELM modelling is introduced, various interpretations of it are given and the need for it is discussed. Then follows an overview of different techniques and methods used in integrated ELM modelling presented roughly according to physics approached in use and in order of increasing complexity. The paper concludes with a short discussion of open issues and future modelling requirements within the field of integrated ELM modelling.
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| 5. |
- Pankin, A. Y., et al.
(författare)
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Extending the validation of multi-mode model for anomalous transport to high beta poloidal tokamak scenario in DIII-D
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:5
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Tidskriftsartikel (refereegranskat)abstract
- The Multi-Mode Model (MMM7.1) for anomalous transport is tested in predictive modeling of temperature profiles of a high beta poloidal DIII-D discharge. This new H-mode plasma regime, with high beta poloidal and high bootstrap currents, has been studied in DIII-D tokamak discharges [A. Garofalo et al., Nucl. Fusion 55, 123025 (2015)]. The role of instabilities that can drive the anomalous transport described by MMM7.1 is investigated. The temperature profiles for a high beta poloidal DIII-D discharge are computed using the NCLASS model for the neoclassical transport and the Weiland and Electron Temperature Gradient (ETG) components of the MMM7.1 model for the anomalous transport. The neoclassical transport is found to be the main contributor to the ion thermal transport in the plasma core. The contributions from the ion temperature gradient driven modes are found to be important only outside of the internal transport barrier. The magnitudes of the predicted temperature profiles are found to be in a reasonable agreement with experimental profiles. The simulation results approximately reproduce the internal transport barrier in the ion temperature profile but not in the electron temperature profile due to a weak dependence of the ETG driven transport on the Shafranov shift in the ETG component of MMM7.1. Possible effects that can contribute to stabilization of these modes, for example, effects associated with the large beta poloidal such as the Shafranov shift stabilization in the MMM7.1 model, are discussed. It is demonstrated that the E x B flow shear has a relatively small effect in the formation of the internal transport barrier in the high beta poloidal DIII-D discharge 154406. The Shafranov shift (alpha stabilization) and small or reversed magnetic shear profiles are found to be the primary reasons for quenched anomalous transport in this discharge. Published by AIP Publishing.
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| 6. |
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| 7. |
- Kritz, A.H., et al.
(författare)
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PTRANSP: Predictive Integrated Tokamak Modeling
- 2009
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Ingår i: 36th European Physical Society Conference on Plasma Physics 2009, EPS 2009; Sofia; Bulgaria; 29 June 2009 through 3 July 2009. - 9781622763368 ; 33E, s. 905-908
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Konferensbidrag (refereegranskat)
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| 8. |
- Pankin, A. Y., et al.
(författare)
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UNDERSTANDING AND PREDICTION OF INTERNAL TRANSPORT BARRIERS IN TOKAMAKS USING INTEGRATED MODELING
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Internal transport barriers (ITBs) are regions of plasmas in tokamak discharges with strongly reduced anomalous transport. The ITB formation can lead to the improvement of energy and particle confinement. Some advanced tokamak scenarios rely on the ITB formation in the plasma core. In particular, the high beta poloidal scenario that has been recently studied on the DIII-D and EAST tokamaks depends on the ITB formation at large radii 1 . It is generally believed that ITBs are triggered by a large ExB flow shear and by a small or reversed magnetic shear. However, the analysis of DIII-D experimental data shows that the ExB flow shear plays a small role in the ITB formation in high β p discharges. Using the integrated modeling approach, we demonstrate that the ITBs in these discharges require a combination of large Shafranov shift and reversed magnetic shear. The ExB flow shear indeed does not play a role in the ITB triggering. In addition, it is demonstrated that the ITB formation depends on the q profiles. An increased plasma current can result in a disappearance of ITB. The dependences of ITB on the Shafranov shift, magnetic shear, and q-profiles can be explained from the analysis of the anomalous transport in high beta poloidal discharges. Theory-based Weiland transport model 2 that predict the anomalous transport driven by ion-temperature gradient driven modes, trapped electron modes and some other MHD modes shows a significant quenching effect from the Shafranov shift. The q-profiles are also found important for the formation of transport barriers in the high beta poloidal DIII-D discharges. The gyro-kinetic GTC simulation confirms the anomalous transport trends observed with the theory-based Weiland model. The observed requirements for the ITB formation can be used in the integrated predictive modeling to optimize the high beta poloidal discharge scenarios in DIII-D, EAST and other tokamaks.
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| 9. |
- Rafiq, Tariq, 1971, et al.
(författare)
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Microtearing modes in tokamak discharges
- 2016
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- Microtearing modes (MTMs) have been identified as a source of significant electron thermaltransport in tokamak discharges. In order to describe the evolution of these discharges, it isnecessary to improve the prediction of electron thermal transport. This can be accomplished byutilizing a model for transport driven by MTMs in whole device predictive modeling codes. Theobjective of this paper is to develop the dispersion relation that governs the MTM driven transport.A unified fluid/kinetic approach is used in the development of a nonlinear dispersion relation forMTMs. The derivation includes the effects of electrostatic and magnetic fluctuations, arbitraryelectron-ion collisionality, electron temperature and density gradients, magnetic curvature, and theeffects associated with the parallel propagation vector. An iterative nonlinear approach is used tocalculate the distribution function employed in obtaining the nonlinear parallel current and the nonlineardispersion relation. The third order nonlinear effects in magnetic fluctuations are included,and the influence of third order effects on a multi-wave system is considered. An envelope equationfor the nonlinear microtearing modes in the collision dominant limit is introduced in order to obtainthe saturation level. In the limit that the mode amplitude does not vary along the field line, slab geometry,and strong collisionality, the fluid dispersion relation for nonlinear microtearing modes isfound to agree with the kinetic dispersion relation. Published by AIP Publishing.[http://dx.doi.org/10.1063/1.4953609]I. INTRODUCTIONMicro-instabilities can result in turbulence that influencesenergy confinement in tokamak discharges. One suchmicro-instability is the microtearing mode (MTM), atearing-parity mode centered on high-order rational surfaces.Microtearing instability can provide a significant contributionto the electron thermal transport in low-aspect ratiotokamaks.1–5 The MTMs lead to a tearing and subsequentreconnection of the magnetic field. MTMs are shortwavelengthion scale (low kh) electromagnetic instabilitiesthat are driven by electron temperature gradients.6–8 It wasproposed that when the magnetic field has a component inthe same direction as the electron temperature gradient, acurrent is driven in the direction of the magnetic field line,which can destabilize MTMs. These modes propagate in theelectron diamagnetic drift direction and depend on the electronion collisionality.9,10 Consequently, transport driven byMTM instabilities depends on both the electron ion collisionfrequency and the electron temperature gradient. Theresearch carried out in this paper indicates that when theelectrostatic effects are included, MTMs also depend on thedensity gradient.
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| 10. |
- Rafiq, T., et al.
(författare)
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Physics basis of Multi-Mode anomalous transport module
- 2013
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 20:3
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Tidskriftsartikel (refereegranskat)abstract
- The derivation of Multi-Mode anomalous transport module version 8.1 (MMM8.1) is presented. The MMM8.1 module is advanced, relative to MMM7.1, by the inclusion of peeling modes, dependence of turbulence correlation length on flow shear, electromagnetic effects in the toroidal momentum diffusivity, and the option to compute poloidal momentum diffusivity. The MMM8.1 model includes a model for ion temperature gradient, trapped electron, kinetic ballooning, peeling, collisionless and collision dominated magnetohydrodynamics modes as well as model for electron temperature gradient modes, and a model for drift resistive inertial ballooning modes. In the derivation of the MMM8.1 module, effects of collisions, fast ion and impurity dilution, non-circular flux surfaces, finite beta, and Shafranov shift are included. The MMM8.1 is used to compute thermal, particle, toroidal, and poloidal angular momentum transports. The fluid approach which underlies the derivation of MMM8.1 is expected to reliably predict, on an energy transport time scale, the evolution of temperature, density, and momentum profiles in plasma discharges for a wide range of plasma conditions.
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