| 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. |
- 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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| 3. |
- Maddison, P, et al.
(författare)
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The rate and pattern of organ damage in late onset systemic lupus erythematosus
- 2002
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Ingår i: Journal of Rheumatology. - 0315-162X. ; 29:5, s. 913-917
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To compare the extent and type of damage in patients with late onset and earlier onset Systemic lupus erythematosus (SLE) using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI). Methods. A total of 86 SLE patients with disease onset after the age of 54 years were matched for center, sex, and ethnic origin with 155 SLE patients with disease onset before the age of 40 years. SDI scores were obtained at one year and 5 years after the diagnosis of SLE. Analysis was based on conditional logistic regression. Results. SDI scores were higher in the late onset group than in younger patients at both one [mean 0.7 (range 0-3) vs 0.3 (range 0-3). p < 0.001] and 5 years [mean 1.6 (range 0-8) vs 0.9 (range 0-7); p < 0.001] after diagnosis. There was also a difference in the pattern of organ damage. While damage to the skin, kidneys, and central nervous system occurred with similar frequency, late onset disease was characterized by significantly more cardiovascular (OR 14.13, p < 0.001). ocular (OR 9.38, p 0.001), and musculoskeletal (OR 2.68, p = 0.016) damage and malignancy (OR 7.04, 3 = 0.046). Conclusion. The occurrence of organ damage assessed by the SDI is greater in patients with late onset SLE than in younger patients and, by this criterion, lupus cannot be judged to be more benign in this age group. Also, the pattern of damage is different, but whether this reflects age per se or the effect of the disease in the elderly remains to be established.
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| 4. |
- Maddison, G. P., et al.
(författare)
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Impurity-seeded plasma experiments on JET
- 2003
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:1, s. 49-62
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Tidskriftsartikel (refereegranskat)abstract
- Scaling to larger tokamaks of high confinement plasmas with radiating edges, induced by impurities, is being studied through internationally collaborative experiments on JET. In campaigns till the end of 2000, three different regimes have been explored. A small number of limiter L-mode discharges seeded with neon have most closely repeated the approach used on TEXTOR-94, but different collisionality and particle transport in JET impede central peaking of the density associated with improved confinement. Divertor L-modes at intermediate density, again with neon injection, have pursued transiently enhanced states found on DIII-D. Confinement up to H-mode quality, together with radiation fractions of approximate to40%, have briefly been obtained, though central Z(eff) quickly increases. Most effectively, neon and argon seeding of higher density ELMy H-modes formed mainly at low triangularity on the septum of the MkIIGB divertor, resembling a pumped-limiter arrangement, have been examined. Good confinement has been sustained at densities close to the Greenwald level in 'afterpuff' (AP) phases following the end of main gas fuelling, for little change of central Z(eff) but up to approximate to60% radiation. Outstanding normalized properties up to H-97 = 0.99 at f(Gwd) = 0.94 have thus been achieved, above the conventional H-mode density limit for diverted plasmas. Stationarity of states has also been extended to many energy confinement times by including low, extra gas inputs in the 'AP', suggestive of an optimized fuelling scheme. Further development in 2001 is reported separately in [1]. Accompanying ELMs are generally reduced in frequency though not evidently in size, electron pedestal pressure being almost unchanged from unseeded behaviour. There are indications of the most favourable impurity species scaling with plasma parameters, performance, radiation and its concentration within a mantle all increasing with argon compared to neon in JET. These benefits in terms of integrated properties are just as required for long burning pulses in ITER, supporting its use of a radiating mantle to assist not only power exhaust but performance too. Impurity-seeded H-modes can therefore contribute directly to next-step scenario development.
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