| 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. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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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.
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| 3. |
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| 4. |
- Bennett, J. M., et al.
(författare)
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GloPL, a global data base on pollen limitation of plant reproduction
- 2018
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Ingår i: Scientific Data. - : Nature Publishing Group. - 2052-4463. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Plant reproduction relies on transfer of pollen from anthers to stigmas, and the majority of flowering plants depend on biotic or abiotic agents for this transfer. A key metric for characterizing if pollen receipt is insufficient for reproduction is pollen limitation, which is assessed by pollen supplementation experiments. In a pollen supplementation experiment, fruit or seed production by flowers exposed to natural pollination is compared to that following hand pollination either by pollen supplementation (i.e. manual outcross pollen addition without bagging) or manual outcrossing of bagged flowers, which excludes natural pollination. The GloPL database brings together data from 2969 unique pollen supplementation experiments reported in 927 publications published from 1981 to 2015, allowing assessment of the strength and variability of pollen limitation in 1265 wild plant species across all biomes and geographic regions globally. The GloPL database will be updated and curated with the aim of enabling the continued study of pollen limitation in natural ecosystems and highlighting significant gaps in our understanding of pollen limitation.
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| 5. |
- Torrisi, Lorenzo, et al.
(författare)
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Proton driven acceleration by intense laser pulses irradiating thin hydrogenated targets
- 2013
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 272, s. 2-5
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Tidskriftsartikel (refereegranskat)abstract
- The Asterix iodine laser of the PALS laboratory in Prague, operating at 1315 nm fundamental frequency, 300 ps pulse duration, 600 J maximum pulse energy and 1016 W/cm2 intensity, is employed to irradiatethin hydrogenated targets placed in high vacuum. Different metallic and polymeric targets allow togenerate multi-energetic and multi-specie ion beams showing peculiar properties. The plasma obtainedby the laser irradiation is monitored, in terms of properties of the emitted charge particles, by using time-of-flight techniques and Thomson parabola spectrometer (TPS). A particular attention is given tothe proton beam production in terms of the maximum energy, emission yield and angular distributionas a function of the laser energy, focal position (FP), target thickness and composition.
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| 6. |
- Torrisi, Lorenzo, et al.
(författare)
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High intensity laser-generating plasmas in forward direction in thin films and Thomson parabola spectrometer monitorage
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Asterix laser at PALS Laboratory of Prague, operating at 1315 nm fundamental wavelength, 300 ps pulse duration, 1016 W/cm2 intensity and single pulse mode, was employed to irradiate thin hydrogenated targets placed in high vacuum. Non-equilibrium plasmas were obtained in forward direction, i.e. along the normal to the target surface on the rear of the irradiated thin films. Plasmas were monitored with different ion detectors, placed around the direction normal to the target. The main detector was a Thomson parabola spectrometer aligned along the normal in forward direction. This spectrometer permits to provide many plasma parameters concerning the involved ions (energy, charge state, mass,...) obtained in a single laser shot. The spectrometer images, obtained by using a MCP coupled to a fast CCD camera, can be processed by a comparison with the simulation data obtained by a proper software. High ion energies and charge states have been obtained as a function of the laser parameters, target thickness and composition and irradiation conditions.
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| 7. |
- Badziak, J., et al.
(författare)
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Application of ion diagnostics to control the laser-induced removal of surface layer of a carbon substrate
- 2006
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Ingår i: Plasma 2005. - : AIP. - 073540304X ; , s. 295-298
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Konferensbidrag (refereegranskat)abstract
- Among other methods of detritiation of in-vessel tokamak components the application of lasers for removal of fuel trapped in co-deposited layers is under investigation. The paper presents preparation and tests of ion diagnostic methods for on-line measurement of the amount and characteristics of ablated carbon, hydrogen/deuterium and contaminant species from the graphite target (plate) of the main toroidal limiter of the TEXTOR tokamak. For removal of the surface layer from the graphite limiter plate Nd:YAG laser was used. Determination of the characteristics of laser-produced ions has been performed by means of ion collectors and an electrostatic ion-energy analyser. The main ion stream parameters were measured depending on the number of laser shots and the laser power density on the target surface. The properties of modified carbon sample surface were determined with the use of optical methods and compared with the results of the ion measurements.
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| 8. |
- Gasior, P., et al.
(författare)
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Characterization of laser-irradiated co-deposited layers on plasma facing components from a tokamak
- 2006
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T123, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- An experimental setup and ion diagnostic method for laser-induced fuel removal and decomposition of co-deposited layers on plasma facing components from tokamaks are described. Nd:YAG 3.5 ns pulse laser with a repetition rate of 10 Hz and single-pulse energy of up to 0.8J at 1.06 mu m has been used for irradiation of a graphite limiter tile from the TEXTOR tokamak. Comparative studies have been performed for a pure graphite plate as a reference target. Energy of emitted ions has been measured using a time-of-flight method. Early results show that laser pulses efficiently ablate the co-deposit removing both fuel species and heavy components such as Si, Ni, Cr, Fe and W present in the layers. Surface topography of the irradiated targets is also presented.
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| 9. |
- Gasior, P., et al.
(författare)
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Effective laser-induced removal of co-deposited layers from plasma-facing components in a tokamak
- 2006
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Ingår i: Czechoslovak Journal of Physics. - : Springer Science and Business Media LLC. - 0011-4626 .- 1572-9486. ; 56, s. B67-B72
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Tidskriftsartikel (refereegranskat)abstract
- An experimental set-up and spectroscopy diagnostic method for laser-induced fuel removal and decomposition of co-deposited layers on plasma-facing components from tokamaks are described. For irradiation of a graphite limiter tile from the TEXTOR tokamak Nd:YAG 3.5-ns pulse laser with a repetition rate of 10 Hz and single pulse energy of up to 0,8 J at 1,06 mu m has been used. The spectroscopy system allowed recording of spectra in the visible wavelength range including CII and D alpha spectral lines. The evolution of CII and Da spectral lines was observed pulse-by-pulse during the co-deposit removal. The efficient ablation of the 45 mu m thick co-deposit occured after approximately 50 laser pulses.
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| 10. |
- Gasior, P., et al.
(författare)
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Laser-induced removal of co-deposits from graphitic plasma-facing components : Characterization of irradiated surfaces and dust particles
- 2009
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 585-588
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Tidskriftsartikel (refereegranskat)abstract
- Laser-induced fuel desorption and ablation of co-deposited layers on limiter plates from the TEXTOR tokamak have been studied. Gas phase composition was monitored in situ, whereas the ex situ studies have been focused on the examination of irradiated surfaces and broad analysis of dust generated by ablation of co-deposits. The size of the dust grains is in the range of few nanometers to hundreds of micrometers. These are fuel-rich dust particles, as determined by nuclear reaction analysis. The presence of deuterium in dust indicates that not all fuel species are transferred to the gas phase during irradiation. This also suggests that photonic removal of fuel and the ablation of co-deposit from plasma-facing components may lead to the redistribution of fuel-containing dust to surrounding areas.
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