| 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. |
- Andersson, Jonas, 1977-, et al.
(författare)
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Effects of heavy endurance physical exercise on inflammatory markers in non-athletes
- 2010
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Ingår i: Atherosclerosis. - : Elsevier BV. - 0021-9150 .- 1879-1484. ; 209:2, s. 601-605
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: Physical activity has beneficial effects on cardiovascular disease but the mechanisms are still somewhat unclear. One possible pathway may be through the anti-inflammatory effects attributed to regular physical activity. Our primary aim was to study the effects of endurance physical exercise on C-reactive protein (CRP), Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNFalpha) during the acute and recovery phases. Secondarily, we studied the impact of diet on these inflammatory markers.METHODS: Twenty men, aged 18-55 years, participated in a 14 days cross-country skiing tour. They traveled 12-30km per day corresponding to about 10h of heavy physical activity. The participants were randomized to a diet with either 30 or 40% of energy derived from fat. Inflammatory variables were analysed at week 0, after 1 and 2 weeks and during the recovery phase at week 6 and 8.RESULTS: CRP and TNFalpha increased significantly during the two weeks of exercise (1.4-5.0mg/l, p=0.00 and 6.8-8.4pg/ml, p=0.00). CRP levels were significantly lower during recovery (median 0.7mg/l) compared to baseline (median 1.4mg/l) and did not correlate to metabolic variables. There were no significant changes in IL-6 levels during the study period. For dietary groups significant CRP changes were observed only in the high fat group during recovery.CONCLUSIONS: CRP and TNFalpha increased significantly but reacted differently during heavy physical activity while there seemed to be no significant changes in IL-6. No significant differences regarding inflammatory variables were found between the dietary groups.
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| 3. |
- Hannan, Abdul, et al.
(författare)
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A Fokker-Planck Code for Fast Self-Consistent Calculations of ICRH
- 2010
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Ingår i: 37th EPS Conference on Plasma Physics.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modeling of ion cyclotron resonant heating, ICRH, requires self-consistent modeling of the distribution function of the resonant ion species and the wave field. A method has been devised for fast self-consistent calculation of the distribution function and the wave field for ICRH modeling. The distribution function is obtained by solving a pitch angle averaged 1D time dependent Fokker Planck equation that includes the Coulomb collision and quasi-linear operators. The quasi-linear operators describing the wave-particle interactions are obtained from the LION code [1]. The time dependent 1D Fokker-Planck equation solved with a cubic finite element method will be presented in this report. The modifications of the susceptibility tensors of the resonant ion species due to changes of the distribution functions caused by heating are calculated by the Fokker-Planck solver and then used in the LION code for calculating the modified wave field
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| 4. |
- Hannan, Abdul, et al.
(författare)
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Fast wave current drive scenarios for DEMO
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:4, s. 043005-
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Tidskriftsartikel (refereegranskat)abstract
- Scenarios for non-inductive current drive using the fast magnetosonic wave in the ion cyclotron range of frequencies in DEMO have been studied. The strong ion cyclotron damping and large Doppler broadening of the alpha particles are shown to limit the possible current drive scenarios to four frequency bands. However, these scenarios may be compromised in the presence of impurities with unfavourable charge to mass ratio. For each frequency the current drive efficiency is optimized with respect to the parallel wave number. The optimized current drive efficiencies are comparable to that from neutral beam injection and electron cyclotron heating, and thus the ion cyclotron range of frequencies should remain a candidate for driving the non-inductive current in DEMO.
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| 5. |
- Hannan, Abdul, 1979-
(författare)
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Modelling Ion Cyclotron Resonance Heating and Fast Wave Current Drive in Tokamaks
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fast magnetosonic waves in the ion cyclotron range of frequencies have the potential to heat plasma and drive current in a thermonuclear fusion reactor. A code, SELFO-light, has been developed to study the physics of ion cyclotron resonantheating and current drive in thermonuclear fusion reactors. It uses a global full wave solver LION and a new 1D Fokker-Planck solver for the self-consistent calculations of the wave field and the distribution function of ions.In present day tokamak experiments like DIII-D and JET, fast wave damping by ions at higher harmonic cyclotron frequencies is weak compared to future thermonuclear tokamak reactors like DEMO. The strong damping by deuterium, tritium and thermonuclear alpha-particles and the large Doppler width of fast alpha-particles in DEMO makes it difficult to drive the current when harmonic resonance layers of these ionspecies are located at low field side of the magnetic axis. At higher harmonic frequencies the possibility of fast wave current drive diminishes due to the overlapping of alpha-particle harmonic resonance layers. Narrow frequency bands suitable for the fast wave current drive in DEMO have been identified at lower harmonics of the alpha-particles. For these frequencies the effect of formation of high-energy tails in the distribution function of majority and minority ion species on the current drive have been studied. Some of these frequencies are found to provide efficient ion heating in the start up phase of DEMO. The spectrum where efficient current drive can be obtained is restricted due to weak electron damping at lower toroidal mode numbers and strong trapped electron damping at higher toroidal mode numbers. The width of toroidal mode spectra for which efficient current drive can be obtained have been identified, which has important implications for the antenna design.
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| 6. |
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| 7. |
- Hellsten, Torbjörn, et al.
(författare)
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A dielectric response model for FEM solutions of ICRF wave fields
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 401:1, s. 012009-
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Tidskriftsartikel (refereegranskat)abstract
- Modelling of fast wave ICRF heating in large machines with high density such as DEMO is challenging because of the short wave lengths. Therefore, fast, efficient global wave solvers are necessary. A major difficulty with calculating the wave field in a spatial dispersive medium is that the dielectric tensor becomes a function of the local wave vector, which in its turn depends on the solution. Furthermore, the solution may consist of several waves co-existing at the same location subjected to separate response functions. In order to model upshift of the parallel wave vector, higher order FLR-effects on the cyclotron absorption and TTMP damping for the electron absorption methods based on iteration, suitable for FEM codes, are proposed.
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| 8. |
- Hellsten, Torbjörn, et al.
(författare)
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A model for self-consistent simulation of ICRH suitable for integrating modelling
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 53:9, s. 093004-
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Tidskriftsartikel (refereegranskat)abstract
- A self-consistent modelling of ion cyclotron resonance heating (ICRH) is reviewed with the aim of obtaining a fast robust scheme suitable for routine simulation for transport codes and data analysis. Due to the complexity of calculating the wave field and the distribution function self-consistently simplifications are necessary. To improve modelling of the wave field, methods are developed to include higher order finite Larmor radius terms, up-and downshifts of the parallel wave number and to improve calculations of damping due to the transit time magnetic pumping in finite element wave codes without decomposing the wave locally into planar waves. A new code, SELFO-light, for self-consistent modelling of ion cyclotron heating suitable for routine calculations is developed. The code is based on coupling the global wave code LION with a simple one-dimensional time-dependent Fokker-Planck code. Both the wave and the Fokker-Planck codes use finite element representations. The importance of self-consistent modelling of ion cyclotron heating is illustrated by studying the effect on the power partition for a fast wave current drive scenario at lower harmonic resonances in a deuterium plasma. It is found that the fraction of the power absorbed on the deuterium and the time to reach the steady state vary strongly depending on the position of the resonances. It is found that the deuterium absorption becomes strongly localized to regions where the resonances are tangential to the magnetic flux surfaces.
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| 9. |
- Hellsten, Torbjörn, et al.
(författare)
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An iterative method for including Doppler shift in global wave solvers using FEM decomposition
- 2014
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Ingår i: Journal of Physics: Conference series. - : Institute of Physics (IOP). - 1742-6596 .- 1742-6588. ; 561
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Tidskriftsartikel (refereegranskat)abstract
- A method for calculating the wave field for spatial dispersive media is proposed suitable for FEM. The method is based on operator splitting by separating the induced current and wave field calculations, and solving the system by means of iterations. In order to take into account several coexisting waves with different poloidal mode numbers when calculating the induced current the wave field is decomposed into wavelets, for which the current is calculated assuming the plasma to be weakly non-uniform.
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| 10. |
- Hellsten, Torbjörn
(författare)
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Momentum transport by wave-particle interaction
- 2011
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Ingår i: PLASMA PHYS CONTROL FUSION. - : IOP Publishing. ; , s. 054007-
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Konferensbidrag (refereegranskat)abstract
- Energy and momentum can be transported across the plasma by waves emitted at one place and absorbed at another. Exchange of momentum and energy between the particles and the waves change the drift orbits, which may give rise to a non-ambipolar particle transport. The main effect of the non-ambipolar transport and quasi-neutrality is a toroidal precession of the trapped particles, which together with the changes in the parallel velocities of the passing resonant particles conserve the toroidal momentum. Non-resonant interactions can give rise to a net change of the local wave number in spatial inhomogeneous plasmas with a resulting force on the medium. Both resonant and non-resonant interactions have to be taken into account in order to have a consistent description of the momentum transported by the waves. The momentum transfer is, in particular, important for waves with short wave length and low frequency, and may explain the enhanced rotation seen in some mode conversion experiments, when the fast magnetosonic wave is converted to an ion-cyclotron wave. The apparent contradiction that the wave momentum may change due to non-resonant wave-particle interactions without changing the energy in geometric optics is explained.
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