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- Fasoli, A., et al.
(författare)
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Chapter 5 : Physics of energetic ions
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 47:6, s. S264-S284
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Forskningsöversikt (refereegranskat)abstract
- This chapter reviews the progress accomplished since the redaction of the first ITER Physics Basis (1999 Nucl. Fusion 39 2137-664) in the field of energetic ion physics and its possible impact on burning plasma regimes. New schemes to create energetic ions simulating the fusion-produced alphas are introduced, accessing experimental conditions of direct relevance for burning plasmas, in terms of the Alfvenic Mach number and of the normalised pressure gradient of the energetic ions, though orbit characteristics and size cannot always match those of ITER. Based on the experimental and theoretical knowledge of the effects of the toroidal magnetic field ripple on direct fast ion losses, ferritic inserts in ITER are expected to provide a significant reduction of ripple alpha losses in reversed shear configurations. The nonlinear fast ion interaction with kink and tearing modes is qualitatively understood, but quantitative predictions are missing, particularly for the stabilisation of sawteeth by fast particles that can trigger neoclassical tearing modes. A large database on the linear stability properties of the modes interacting with energetic ions, such as the Alfven eigenmode has been constructed. Comparisons between theoretical predictions and experimental measurements of mode structures and drive/damping rates approach a satisfactory degree of consistency, though systematic measurements and theory comparisons of damping and drive of intermediate and high mode numbers, the most relevant for ITER, still need to be performed. The nonlinear behaviour of Alfven eigenmodes close to marginal stability is well characterized theoretically and experimentally, which gives the opportunity to extract some information on the particle phase space distribution from the measured instability spectral features. Much less data exists for strongly unstable scenarios, characterised by nonlinear dynamical processes leading to energetic ion redistribution and losses, and identified in nonlinear numerical simulations of Alfven eigenmodes and energetic particle modes. Comparisons with theoretical and numerical analyses are needed to assess the potential implications of these regimes on burning plasma scenarios, including in the presence of a large number of modes simultaneously driven unstable by the fast ions.
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| 3. |
- Haugen, O., et al.
(författare)
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High resolution thermal imaging of hotspots in superconducting films
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 17:2/3, s. 3215-3218
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Tidskriftsartikel (refereegranskat)abstract
- Thermal imaging of hotspots in bridge structures of YbaCuO thin films is presented with micrometer resolution. Hotspots formed by passing transport currents are observed using a method based on the temperature dependence in the photoluminescence of a polymer thin film deposited on the superconductor. The hotspots are self maintained and have hysteretic behavior. An external magnetic field changes their behavior. The temperature distribution over the bridge and in its vicinity can be observed with a resolution better than 0.1 K. Also details of the experimental method will be reported.
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| 4. |
- Santala, M. I. K., et al.
(författare)
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Proton-triton nuclear reaction in ICRF heated plasmas in JET
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 48:8, s. 1233-1253
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Tidskriftsartikel (refereegranskat)abstract
- Fast protons can react with tritons in an endothermic nuclear reaction which can act as a source of neutrons in magnetically confined fusion plasmas. We have performed an experiment to systematically study this reaction in low tritium concentration (approximate to 1%) plasmas in the Joint European Torus. A linear dependence is found between excess neutron rate and tritium concentration when the DT fusion rate is low. We discuss the properties of the neutron emission, including anisotropy, from the proton-triton reaction in a fusion reactor environment and derive simple models for the calculation of the neutron yield from this reaction in terms of tritium density, fast ion temperature and fast ion energy content.
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| 5. |
- Sharapov, S. E., et al.
(författare)
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Chapter 5 - Burning plasma studies at jet
- 2008
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 53:4, s. 989-1022
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Tidskriftsartikel (refereegranskat)abstract
- Studies establishing key phenomena and developing diagnostics for energetic particle physics, which are essential for the next step burning plasma experiments such as the International Thermonuclear Experimental Reactor (ITER), have been performed at the Joint European Torus (JET). Experiments have demonstrated clear self-heating of deuterium-tritium (D-T) plasma by alpha particles as a maximum in electron temperature at an optimum mixture of 60 +/- 20% tritium. The change in electron temperature produced by alpha heating, Delta T-e(0) = 1.3 +/- 0.23 keV, was as expected from classical heating, whereas the heating of thermal ions was higher than expected from reference deuterium discharges. Alfven eigenmodes were stable in the highest fusion performance D-T plasmas, in agreement with the modeling. Systematic studies on the existence and properties of Alfven eigenmodes with external antenna driving and detecting Alfven eigenmodes are presented. The formation of fuel ion tails due to alpha-particle knock-on effects is described as derived from neutral particle analyzer and neutron emission spectrometry in D-T experiments. The gamma-ray diagnostics are shown to measure Profiles and energy distribution functions of high-energy ions and alpha particles. Time- and space-resolved gamma-ray images demonstrated for the first time the possibility of measuring several types of energetic ions simultaneously. The novel technique of detecting unstable Alfven eigenmodes with interferometry is found to be superior in detecting core-localized Alfven eigenmodes.
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- Testa, A. C., et al.
(författare)
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Intravenous contrast ultrasound examination using contrast-tuned imaging (CnTI (TM)) and the contrast medium SonoVue (R) for discrimination between benign and malignant adnexal masses with solid components
- 2009
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Ingår i: Ultrasound in Obstetrics & Gynecology. - : Wiley. - 1469-0705 .- 0960-7692. ; 34:6, s. 699-710
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Tidskriftsartikel (refereegranskat)abstract
- Objective To determine whether intravenous contrast ultrasound examination is superior to gray-scale or power Doppler ultrasound for discrimination between benign and malignant adnexal masses with complex ultrasound morphology. Methods In an international multicenter study, 134 patients with an ovarian mass with solid components or a multilocular cyst with more than 10 cyst locules, underwent a standardized transvaginal ultrasound examination followed by contrast examination using the contrast-tuned imaging technique and intravenous injection of the contrast medium SonoVue (R). Time intensity curves were constructed, and peak intensity, area under the intensity curve, time to peak, sharpness and half wash-out time were calculated. The sensitivity and specificity with regard to malignancy were calculated and receiver-operating characteristics (ROC) curves were drawn for gray-scale, power Doppler and contrast variables and for pattern recognition (subjective assignment of a certainly benign, probably benign, uncertain or malignant diagnosis, using gray-scale and power Doppler ultrasound findings). The gold standard was the histological diagnosis of the surgically removed tumors. Results After exclusions (surgical removal of the mass > 3 months after the ultrasound examination, technical problems), 72 adnexal masses with solid components were used in our statistical analyses. The values for peak contrast signal intensity and area under the contrast signal intensity curve in malignant tumors were significantly higher than those in borderline tumors and benign tumors, while those for the benign and borderline tumors were similar. The area under the ROC curve of the best contrast variable with regard to diagnosing borderline or invasive malignancy (0.84) was larger than that of the best gray-scale (0.75) and power Doppler ultrasound variable (0.79) but smaller than that of pattern recognition (0.93). Conclusion Findings on ultrasound contrast examination differed between benign and malignant tumors but there was a substantial overlap in contrast findings between benign and borderline tumors. It appears that ultrasound contrast examination is not superior to conventional ultrasound techniques, which also have difficulty in distinguishing between benign and borderline tumors, but can easily differentiate invasive malignancies from other tumors. Copyright (C) 2009 ISUOG. Published by John Wiley & Sons, Ltd.
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