| 1. |
- Ongena, J., et al.
(författare)
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Recent progress on JET towards the ITER reference mode of operation at high density
- 2001
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 43, s. A11-A30
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress towards obtaining high density and high confinement in JET as required for the ITER reference scenario at Q = 10 is summarized. Plasmas with simultaneous confinement H-98(y.2) = 1 and densities up to n/n(Gw) similar to 1 are now routinely obtained. This has been possible (i) by using plasmas at high (delta similar to 0.5) and medium (delta similar to 0.3-0.4) triangularity with sufficient heating power to maintain Type I ELMs, (ii) with impurity seeded plasmas at high (delta similar to 0.5) and low (delta less than or equal to 0.2) triangularity, (iii) with an optimized pellet injection sequence, maintaining the energy confinement and raising the density, and (iv) by carefully tuning the gas puff rate leading to plasmas with peaked density profiles and good confinement at long time scales. These high performance discharges exhibit Type I ELMs, with a new and more favourable behaviour observed at high densities, requiring further studies. Techniques for a possible mitigation of these ELMs are discussed, and first promising results are obtained with impurity seeding in discharges at high triangularity. Scaling studies using the new data of this year show a strong dependence of confinement on upper triangularity, density and proximity to the Greenwald limit. Observed MHD instabilities and methods to avoid these in high density and high confinement plasmas are discussed.
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| 2. |
- Sips, A. C. C., et al.
(författare)
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An international database for the study of the formation of ITBs in tokamaks
- 2002
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 44, s. A391-A398
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, data from eight,different tokamaks have been combined in an international database for internal transport barriers (ITBs). An analysis of the data for the formation of an ITB with dominant ion heating shows a clear dependence of the threshold power on the minor radius and line-averaged electron density for the formation of ion ITBs. The dependence of ITB formation on the toroidal magnetic field is weak. For the formation of ITBs with dominant electron heating, the database is smaller, but for the threshold power a strong increase with plasma size and a weak toroidal field dependence could also be identified. Based on these results, an expression for the power required to form an ITB is given using global variables only. These results give a basis for the analysis of the database using local values (like magnetic shear) and a detailed comparison with theory-based models.
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| 3. |
- McDonald, C., et al.
(författare)
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ELMy H-modes in JET helium-4 plasmas
- 2004
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 46:3, s. 519-534
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Tidskriftsartikel (refereegranskat)abstract
- ELMy H-modes in helium-4 plasmas provide valuable information on ELMy H-mode physics as well as a possible early low activation operational phase for next-step tokamaks, such as ITER. With this in mind, a series of helium-4 H-mode experiments were performed on JET with pure helium-4 NBI auxiliary heating (up to 12 MW). A set of ELMy H-mode plasmas were produced, in both the Type I ELM regime and a second regime, which showed characteristics similar to the deuterium Type III regime, but with a reverse ELM frequency dependence on power. Sawteeth were also observed, and had similar behaviour to those seen in deuterium. Compared with deuterium plasmas, Type I ELMy H-mode confinement is seen to be 28 +/- 6% poorer in helium-4 plasmas and the L-H power threshold 42 +/- 10% larger. This is the opposite of the behaviour predicted by experimental isotope mass scalings from hydrogenic plasmas.Comparison with a wider hydrogenic database, enables the effects of isotopic charge and mass to be studied independently.
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| 4. |
- Loarte, A., et al.
(författare)
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Characterization of pedestal parameters and edge localized mode energy losses in the Joint European Torus and predictions for the International Thermonuclear Experimental Reactor
- 2004
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 11:5, s. 2668-2678
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the experimental characterization of pedestal parameters, edge localized mode (ELM) energy, and particle losses from the main plasma and the corresponding ELM energy fluxes on plasma facing components for a series of dedicated experiments in the Joint European Torus (JET). From these experiments, it is demonstrated that the simple hypothesis relating the peeling-ballooning linear instability to ELM energy losses is not valid. Contrary to previous observations at lower triangularities, small energy losses at low collisionality have been obtained in regimes at high plasma triangularity and q(95)similar to4.5, indicating that the edge plasma magnetohydrodynamic stability is linked with the transport mechanisms that lead to the loss of energy by conduction during type I ELMs. Measurements of the ELM energy fluxes on the divertor target show that their time scale is linked to the ion transport along the field and the formation of a high energy sheath, in agreement with kinetic modeling of ELMs. Higher density ELMs, of a convective nature, lead to overall much longer time scales for the ELM energy flux, with more than 80% of the ELM energy flux arriving after the surface divertor temperature has reached its maximum value. On the contrary, for low density ELMs, of a conductive nature, up to 40% of the energy flux arrives at the divertor target before the surface divertor temperature has reached its maximum value. These large and more conductive ELMs may lead to up to similar to50% of the ELM energy reaching the main wall plasma facing components instead of the divertor target. The extrapolation to the International Thermonuclear Experimental Reactor of the obtained results is described and the main uncertainties discussed.
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| 5. |
- Campbell, D. J., et al.
(författare)
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Report on the 9th European fusion physics workshop
- 2003
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 45:4, s. 505-520
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Tidskriftsartikel (refereegranskat)abstract
- The 9th EFPW took place in December 2001 at Saariselka in Finland, hosted by the Technical Research Centre of Finland (VTT) and the Helsinki University, and sponsored by the European Commission. Within an overall theme of 'transient events, their mitigation and their implications for plasma facing components in ITER', four topics of importance to the future development of magnetically confined fusion were discussed in detail. In addition, the key issues for the ITER design which are associated with transient events and a review of the JET scientific and technical programme under EFDA were presented. The main issues discussed and the areas identified as requiring further study are summarized here.
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| 6. |
- Litaudon, X., et al.
(författare)
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Progress towards steady-state operation and real-time control of internal transport barriers in JET
- 2003
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:7, s. 565-572
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Tidskriftsartikel (refereegranskat)abstract
- In JET, advanced tokamak research mainly focuses on plasmas with internal transport barriers (ITBs) that are strongly influenced by the current density profile. A previously developed optimized shear regime with low magnetic shear in the plasma centre has been extended to deeply negative magnetic shear configurations. High fusion performance with wide ITBs has been obtained transiently with negative central magnetic shear configuration: H-IPB98(y,H-2) similar to 1.9, beta(N) = 2.4 at I-p = 2.5 MA. At somewhat reduced performance, electron and ion ITBs have been sustained in full current drive operation with 1 MA of bootstrap current: H-IPB98(y,H-2) similar to 1, beta(N) = 1.7 at I-p = 2.0 MA. The ITBs were maintained for up to 11 s for the latter case. This duration, much larger than the energy confinement time (37 times larger), is already approaching a current resistive time. New real-time measurements and feedback control algorithms have been developed and implemented in JET for successfully controlling the ITB dynamics and the current density profile in the highly non-inductive current regime.
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| 7. |
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| 8. |
- Tala, TJJ, et al.
(författare)
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Comparison of theory-based and semi-empirical transport modelling in JET plasmas with ITBs
- 2002
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Ingår i: Plasma Physics and Controlled Fusion. - 1361-6587 .- 0741-3335. ; 44:Suppl. 5A, s. A495-A500
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Tidskriftsartikel (refereegranskat)abstract
- The theory-based Weiland transport model has been applied to JET discharges with internal transport barriers (ITBs) for the first time. The agreement of the modelling results with the experiments has been found to be comparable with the agreement of the modelling results produced by the semi-empirical Bohm/gyro-Bohm transport model. Weiland model overestimates the width of the ITB and the electron temperature. There is evidence that the density gradient in the Weiland model plays a more important role in governing the ITB formation dynamics for JET discharges than the suppression of turbulence by the omega(ExB) flow shearing rate.
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