| 1. |
- Abel, I, et al.
(författare)
-
Overview of the JET results with the ITER-like wall
- 2013
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
-
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.
|
|
| 2. |
- Romanelli, F, et al.
(författare)
-
Overview of the JET results
- 2011
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
-
Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
|
|
| 3. |
- Dahl-Jensen, D., et al.
(författare)
-
Eemian interglacial reconstructed from a Greenland folded ice core
- 2013
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 493:7433, s. 489-494
-
Tidskriftsartikel (refereegranskat)abstract
- Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.
|
|
| 4. |
- Leppänen, A. -P, et al.
(författare)
-
Cosmogenic Be-7 in air : A complex mixture of production and transport
- 2010
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:13, s. 1036-1043
-
Tidskriftsartikel (refereegranskat)abstract
- The long-time series of Be-7 activity in surface air have been studied with the wavelet analysis technique in order to find coherence between Be-7 activity, theoretical production in the troposphere and climatic indices. The Be-7 activity were obtained from five different locations, Angra in the tropics in Brazil, Skane in mid-latitudes in Southern Sweden, Kiruna in Polar region in Northern Sweden, Loviisa in Southern Finland and Rovaniemi in polar region in Northern Finland. The Be-7 data from the Northern hemisphere sites where tested for coherence with theoretical production of the isotope in troposphere and with the North Atlantic Oscillation index. In the Southern hemisphere separate theoretical production was calculated in order to describe local production and Southern Annular Mode was used as the climatic index. Consistent and significant coherence were found with theoretical production at Skane, Kiruna and Loviisa at time-scales of four years or longer. At Angra and Rovaniemi sites, no coherence was detected between Be-7 theoretical tropospheric production and measured activity at ground level. The coherence between Be-7 data from Skane and Angra and climatic indices is insignificant while data from Northern and Eastern Scandinavia show clear coherence with climatic indices at time-scales of four years or longer. Additionally, significant coherence was found between the cosmic ray induced production and NAO at the time band of 8-12 years whereas the coherence between cosmic ray induced production and SAM was insignificant. This feature implies that the ground level Be-7 activity contain mixed information on both production and transport. This conclusion means that further evaluation through models which enable accurate realistic models that will be investigated in future studies.
|
|
| 5. |
- Tonkov, S., et al.
(författare)
-
On the Holocene history of sweet chestnut forests in Belasitsa mountain, Southwestern Bulgaria
- 2012
-
Ingår i: Comptes Rendus de l'Academie Bulgare des Sciences / Proceedings of the Bulgarian Academy of Sciences. - 1310-1331 .- 2367-5535. ; 65:11, s. 1549-1554
-
Tidskriftsartikel (refereegranskat)abstract
- The Holocene history of sweet chestnut (Castanea sativa Mill.) on the northern slopes of Belasitsa Mountain was studied by pollen analysis and radiocarbon dating of a core collected from a small mire. The results showed that more than 8000 years ago this tree was spontaneously growing in the mountain before the first Neolithic inhabitants settled in the Struma River Valley and its tributaries. The enlargement of the areas occupied by sweet chestnut started with its wide cultivation since the time of the Roman colonization. The new palynological information supports the hypothesis for possible existence of refugia for Castanea sativa in Southwestern Bulgaria.
|
|
| 6. |
- Berggren, Ann-Marie, et al.
(författare)
-
Variability of 10Be and δ18O in snow pits from Greenland and a surface traverse from Antarctica
- 2013
-
Ingår i: Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry. - : Elsevier BV. ; , s. 568-572
-
Konferensbidrag (refereegranskat)abstract
- To examine temporal variability of 10Be in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of 10Be in glacial ice was explored through collection of the upper ∼5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 10Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the δ18O data. The 10Be concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between 10Be and δ18O, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 10Be concentrations in snow in Queen Maud Land, Antarctica.
|
|
| 7. |
- Borge, M. J. G., et al.
(författare)
-
Rare beta p decays in light nuclei
- 2013
-
Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 40:3, s. art.no. 035109-
-
Tidskriftsartikel (refereegranskat)abstract
- Beta-delayed proton emission may occur at very low rates in the decays of the light nuclei Be-11 and B-8. This paper explores the potential physical significance of such decays, estimates their rates and reports on first attempts to detect them: an experiment at ISOLDE/CERN gives a branching ratio for Be-11 of ( 2.5 +/- 2.5) x 10(-6) and an experiment at JYFL a 95% confidence upper limit of 2.6 x 10(-5) for B-8.
|
|
| 8. |
- Li, Shu-Yi, et al.
(författare)
-
Bandgap widening in thermochromic Mg-doped VO2 thin films : Quantitative data based on optical absorption
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:16, s. 161907-
-
Tidskriftsartikel (refereegranskat)abstract
- Thermochromic Mg-doped VO2 films were deposited by reactive direct current magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were inferred from Rutherford backscattering. Optical bandgaps were obtained from spectral transmittance and reflectance measurements-from both the film side and the back side of the samples-and ensuing determination of absorption coefficients. The bandgap of Mg-doped films was found to increase by 3.9 +/- 0.5 eV per unit of atom ratio Mg/(Mg + V) for 0 < Mg/(Mg + V) < 0.21. The presence of similar to 0.45 at. % Si enhanced the bandgap even more.
|
|
| 9. |
- Vybornov, A., et al.
(författare)
-
Chronological problems with neolithization of the northern caspian sea area and the forest-steppe povolzhye region
- 2012
-
Ingår i: Radiocarbon. - 0033-8222 .- 1945-5755. ; 54:3-4, s. 795-799
-
Tidskriftsartikel (refereegranskat)abstract
- Steppe and forest-steppe areas of the Povolzhye area (Caucasus and central Asia) bear much interest for the Neolithic in connection with the productive economy of the region at the time. Recent data have allowed correction of the region's chronology. A number of C-14 dates denote the existence of the Neolithic in this territory as early as the 5th to 6th millennium BP. However, some questions are still under debate and require further data to clarify.
|
|
| 10. |
- Yi, Peng, et al.
(författare)
-
Circulation of water masses in the Baltic Proper revealed through iodine isotopes
- 2013
-
Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 36, s. 118-124
-
Tidskriftsartikel (refereegranskat)abstract
- Tracer technology has been used to understand water circulation in marine systems where the tracer dose is commonly injected into the marine waters through controlled experiments, accidental releases or waste discharges. Anthropogenic discharges of I-129 have been used to trace water circulation in the Arctic and North Atlantic Ocean. Here, I-129, together with I-127, is utilized as a tracer of water pathways and circulation in the Baltic Sea through collection of seawater depth profiles. The results indicate the presence of I-129 signatures which are distinct for each water mass and provide evidence for: (1) inflow water masses through the Drogden Sill that may reach as far as the SW of the Arkona Sea, (2) a portion of North Atlantic water in the bottom of Arkona basin, (3) cyclonic upwelling which breaks through the halocline in a pattern similar to the Baltic haline conveyor belt and (4) more influx of fresher water from the Gulf of Finland and Bothnian Sea in August relative to April. These findings provide advances in labeling and understanding water pathways in the Baltic Sea.
|
|
