| 1. |
- 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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| 2. |
- Jones, G. H., et al.
(författare)
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The dust halo of Saturn's largest icy moon, Rhea
- 2008
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 319:5868, s. 1380-1384
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Tidskriftsartikel (refereegranskat)abstract
- Saturn's moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturn's magnetosphere. The Cassini spacecraft's in situ observations reveal that energetic electrons are depleted in the moon's vicinity. The absence of a substantial exosphere implies that Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material.
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| 3. |
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| 4. |
- Persoon, A. M., et al.
(författare)
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A diffusive equilibrium model for the plasma density in Saturn's magnetosphere
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:4, s. A04211-
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Tidskriftsartikel (refereegranskat)abstract
- Electron density measurements have been obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument for more than 50 passes through Saturn's inner magnetosphere from 30 June 2004 to 30 September 2007. The electron densities are derived from RPWS measurements of the upper hybrid resonance frequency and span latitudes up to 35 degrees and L values from 3.6 to 10. The electron density measurements are combined with ion anisotropy measurements from the Cassini Plasma Spectrometer (CAPS) and electron temperature measurements from the RPWS and CAPS to develop a diffusive equilibrium model for the distribution of water group ions, hydrogen ions, and electrons in the inner region of Saturn's magnetosphere. The model uses an analytical solution of the field-aligned force equation, including the ambipolar electric field, to determine the equatorial ion densities and scale heights as a function of L. Density contour plots for water group ions, hydrogen ions, and electrons are presented.
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| 5. |
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| 6. |
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| 7. |
- Nordman, Hans, 1957, et al.
(författare)
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Anomalous impurity transport in tokamaks in the presence of RF fields
- 2008
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Ingår i: Proceedings of the 35th EPS Conference on Plasma Physics, Hersonissos, Greece, 9-13 June, 2008, ECA. - 9781622763351 ; 32:2, s. 882-885
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Konferensbidrag (refereegranskat)abstract
- Recent experiments1-4 have shown that auxiliary heating can influence impurity accumulation in Tokamaks. In the present study the transport of impurities by Ion-Temperature-Gradient (ITG) and Trapped-Electron (TE) mode turbulence in the presence of radio frequency (rf) fields in the ion cyclotron range of frequencies is investigated using an electrostatic, collisionless fluid model. The turbulence is affected by the ponderomotive force associated with the rf field of the fast magnetosonic wave in the plasma. It is shown that the inward impurity convective velocity (pinch) and diffusivity can be reduced by the rf field, in particular close to the wave resonance location where the ponderomotive force may be significant. However, the steady state impurity density peaking factor -∇nz/nz does not seem to be as strongly affected by the rf field as indicated by recent tokamak experiments.
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| 8. |
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| 9. |
- Sergienko, G., et al.
(författare)
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Erosion of a tungsten limiter under high heat flux in TEXTOR
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 363, s. 96-100
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Tidskriftsartikel (refereegranskat)abstract
- Erosion characteristics of a tungsten plate heated up in TEXTOR by the plasma load have been investigated at temperatures extending to the melting point. No enhancement of atomic release exceeding physical sputtering and normal thermal sublimation for temperatures below 3700 K was observed. The liquid tungsten moved fast along the plate in the direction perpendicular to the magnetic field lines. The motion is caused by the Lorentz force due to the thermoelectron current emitted from the hot tungsten surface. The motion of liquid tungsten caused a material loss of 2.85 g during two discharges. The material redistribution due to the melt layer motion is compared with a MEMOS-1.5D simulation.
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| 10. |
- Sergienko, G., et al.
(författare)
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Experience with bulk tungsten test-limiters under high heat loads : melting and melt layer propagation
- 2007
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T128, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- The paper provides an overview of processes and underlying physics governing tungsten melt erosion in the fusion plasma environment. Experiments with three different bulk tungsten test-limiters were performed in TEXTOR: (i) thermally insulated solid plate fixed on a graphite roof-like limiter heated up by the plasma to the melting point, (ii) macro-brush of the ITER-relevant castellated structure and (iii) lamellae structure developed for the JET divertor. The main objectives were to determine the metal surface damage, the formation of the melt layer and its motion in the magnetic field. PHEMOBRID-3D and MEMOS-1.5D numerical codes were used to simulate the experiment with the roof-like test-limiter. Both experiments and simulation showed that the melting of tungsten can lead to a large material redistribution due to thermo-electron emission currents without ejection of molten material to the plasma.
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