| 1. |
- 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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| 2. |
- Kaptoge, S., et al.
(författare)
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Whom to treat? The contribution of vertebral X-rays to risk-based algorithms for fracture prediction. Results from the European Prospective Osteoporosis Study
- 2006
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Ingår i: Osteoporosis International. - : Springer Science and Business Media LLC. - 1433-2965 .- 0937-941X. ; 17:9, s. 1369-1381
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Vertebral fracture is a strong risk factor for future spine and hip fractures; yet recent data suggest that only 5-20% of subjects with a spine fracture are identified in primary care. We aimed to develop easily applicable algorithms predicting a high risk of future spine fracture in men and women over 50 years of age. Methods: Data was analysed from 5,561 men and women aged 50+ years participating in the European Prospective Osteoporosis Study (EPOS). Lateral thoracic and lumbar spine radiographs were taken at baseline and at an average of 3.8 years later. These were evaluated by an experienced radiologist. The risk of a new (incident) vertebral fracture was modelled as a function of age, number of prevalent vertebral fractures, height loss, sex and other fracture history reported by the subject, including limb fractures occurring between X-rays. Receiver Operating Characteristic (ROC) curves were used to compare the predictive ability of models. Results: In a negative binomial regression model without baseline X-ray data, the risk of incident vertebral fracture significantly increased with age [RR 1.74, 95% CI (1.44, 2.10) per decade], height loss [1.08 (1.04, 1.12) per cm decrease], female sex [1.48 (1.05, 2.09)], and recalled fracture history; [1.65 (1.15, 2.38) to 3.03 (1.66, 5.54)] according to fracture site. Baseline radiological assessment of prevalent vertebral fracture significantly improved the areas subtended by ROC curves from 0.71 (0.67, 0.74) to 0.74 (0.70, 0.77) P=0.013 for predicting 1+ incident fracture; and from 0.74 (0.67, 0.81) to 0.83 (0.76, 0.90) P=0.001 for 2+ incident fractures. Age, sex and height loss remained independently predictive. The relative risk of a new vertebral fracture increased with the number of prevalent vertebral fractures present from 3.08 (2.10, 4.52) for 1 fracture to 9.36 (5.72, 15.32) for 3+. At a specificity of 90%, the model including X-ray data improved the sensitivity for predicting 2+ and 1+ incident fractures by 6 and 4 fold respectively compared with random guessing. At 75% specificity the improvements were 3.2 and 2.4 fold respectively. With the modelling restricted to the subjects who had BMD measurements (n=2,409), the AUC for predicting 1+ vs. 0 incident vertebral fractures improved from 0.72 (0.66, 0.79) to 0.76 (0.71, 0.82) upon adding femoral neck BMD (P=0.010). Conclusion: We conclude that for those with existing vertebral fractures, an accurately read spine X-ray will form a central component in future algorithms for targeting treatment, especially to the most vulnerable. The sensitivity of this approach to identifying vertebral fracture cases requiring anti-osteoporosis treatment, even when X-rays are ordered highly selectively, exceeds by a large margin the current standard of practice as recorded anywhere in the world.
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| 3. |
- Monier-Garbet, P, et al.
(författare)
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Impurity-seeded ELMy H-modes in JET, with high density and reduced heat load
- 2005
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 45:11, s. 1404-1410
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Tidskriftsartikel (refereegranskat)abstract
- Experiments performed at JET during the past two years show that, in high triangularity H-mode plasmas with I-p = 2.5 MA, n(e)/n(Gr) approximate to 1.0, it is possible to radiate separately up to approximate to 40% of the total injected power on closed flux surfaces in the pedestal region (argon seeding) and up to approximate to 50% of the injected power in the divertor region (nitrogen seeding), while maintaining the confinement improvement factor at the value required for ITER, H98(y, 2) 1.0. The total radiated power fraction achieved in both cases (65-70%) is close to that required for ITER. However, Type I ELMS observed with impurity seeding have the same characteristics as that observed in reference pulses without seeding: decreasing plasma energy loss per ELM with increasing pedestal collisionality. One has to reach the Type III ELM regime to decrease the transient heat load to the divertor to acceptable values for ITER, although at the expense of confinement. The feasibility of an integrated scenario with Type-III ELMS, and q(95) = 2.6 to compensate for the low H factor, has been demonstrated on JET. This scenario would meet ITER requirements at 17 MA provided that the IPB98 scaling for energy content is accurate enough, and provided that a lower dilution is obtained when operating at higher absolute electron density.
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| 4. |
- Tala, T., et al.
(författare)
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Toroidal and poloidal momentum transport studies in tokamaks
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 49:12B, s. B291-B302
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Tidskriftsartikel (refereegranskat)abstract
- The present status of understanding of toroidal and poloidal momentum transport in tokamaks is presented in this paper. Similar energy confinement and momentum confinement times, i.e. tau(E)/tau(phi)approximate to 1 have been reported on several tokamaks. It is more important though, to study the local transport both in the core and edge plasma separately as, for example, in the core plasma, a large scatter in the ratio of the local effective momentum diffusivity to the ion heat diffusivity chi(phi eff)/chi(i.eff) among different tokamaks can be found. For example, the value of effective Prandtl number is typically around chi(phi eff)/chi(i.eff)approximate to 0.2 on JET while still tau(E)/tau(phi)approximate to 1 holds. Perturbative NBI modulation experiments on JET have shown, however, that a Prandtl number chi(phi)/chi(i) of around 1 is valid if there is an additional, significant inward momentum pinch which is required to explain the amplitude and phase behaviour of the momentum perturbation. The experimental results, i.e. the high Prandtl number and pinch, are in good qualitative and to some extent also in quantitative agreement with linear gyro-kinetic simulations. In contrast to the toroidal momentum transport which is clearly anomalous, the poloidal velocity is usually believed to be neo-classical. However, experimental measurements on JET show that the carbon poloidal velocity can be an order of magnitude above the predicted value by the neo-classical theory within the ITB. These large measured poloidal velocities, employed for example in transport simulations, significantly affect the calculated radial electric field and therefore the E x B flow shear and hence modify and can significantly improve the simulation predictions. Several fluid turbulence codes have been used to identify the mechanism driving the poloidal velocity to such high values. CUTIE and TRB turbulence codes and also the Weiland model predict the existence of an anomalous poloidal velocity, peaking in the vicinity of the ITB and driven dominantly by the flow due to the Reynold's stress. It is worth noting that these codes and models treat the equilibrium in a simplified way and this affects the geodesic curvature effects and geodesic acoustic modes. The neo-classical equilibrium is calculated more accurately in the GEM code and the simulations suggest that the spin-up of poloidal velocity is a consequence of the plasma profiles steepening when the ITB grows, following in particular the growth of the toroidal velocity within the ITB.
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| 5. |
- Ongena, J., et al.
(författare)
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Overview of recent results on Heating and Current Drive in JET
- 2007
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Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - : AIP. ; , s. 249-256
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Konferensbidrag (refereegranskat)abstract
- Recent progress on heating and current drive on JET is reported. Topics discussed are: high power coupling of ICRF/LH at ITER relevant antenna/launcher-separatrix distances, succesfull demonstration of 3 dB couplers for ELM tolerance of the ICRF system, influence of ICRF on LH operation, rotation studies in plasma without external momentum with standard and enhanced JET toriodal field ripple, studies of different ICRF heating schemes and of NTM avoidance schemes using Ion Cyclotron Current Drive. A brief outlook on future plans for experiments at JET is given.
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| 6. |
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| 7. |
- Rantamäki, K., et al.
(författare)
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LH wave coupling over ITER-like distances at JET
- 2007
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Ingår i: Radio Frequency Power in Plasmas. - : American Institute of Physics (AIP). - 0735404445 - 9780735404441 ; , s. 261-264
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Konferensbidrag (refereegranskat)abstract
- Good coupling of LH power at plasma-launcher distance of 15 cm has been obtained at JET. Near-gas injection is used to increase the density in front of the grill. The role of LH power in the density increase at constant gas level is demonstrated. For the first time at JET the temperature of the hot spots caused by parasitic absorption of LH power has been measured.
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| 8. |
- Blackwell-Whitehead, R J, et al.
(författare)
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Experimental oscillator strengths for the spectrum of neutral manganese
- 2005
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 361:4, s. 1281-1286
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Tidskriftsartikel (refereegranskat)abstract
- We report laboratory measurements of oscillator strengths for 44 transitions in the Mn T spectrum covering the wavelength range 209-2780 nm. Nine energy level lifetimes have been measured using time resolved laser-induced fluorescence (LIF). The lifetimes have been combined with branching fractions measured by Fourier transform spectroscopy to obtain absolute oscillator strengths. In total, 24 of these oscillator strengths are measured for the first time, including transitions in the previously unobserved infrared region above 2.0 mu m.
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| 9. |
- Blackwell-Whitehead, R. J., et al.
(författare)
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Experimental TiI oscillator strengths and their application to cool star analysis
- 2006
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 373:4, s. 1603-1609
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465-3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for 13 energy levels, including the low energy levels 3d(2)(F-3) 4s4p ((3)p) z(5)D(j)degrees have been measured using time-resolved laser-induced fluorescence. Intensity-calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region lambda > 1.0 mu m, a region of particular interest to the analysis of cool stars and brown dwarfs.
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| 10. |
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