| 1. |
- Romanelli, F, et al.
(author)
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Overview of the JET results
- 2011
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Journal article (peer-reviewed)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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| 2. |
- Abel, I, et al.
(author)
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Overview of the JET results with the ITER-like wall
- 2013
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Journal article (peer-reviewed)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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| 3. |
- Bécoulet, A., et al.
(author)
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Science and technology research and development in support to ITER and the Broader Approach at CEA
- 2013
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10
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Journal article (peer-reviewed)abstract
- In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Corre, Y., et al.
(author)
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Radiated power and impurity concentrations in the EXTRAP-T2R reversed-field pinch
- 2005
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; 71:5, s. 523-531
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Journal article (peer-reviewed)abstract
- A numerical and experimental study of the impurity concentration and radiation in the EXTRAP-T2R device is reported. The experimental setup consists of an 8-chord bolometer system providing the plasma radiated power and a vacuum-ultraviolet spectrometer providing information on the plasma impurity content. The plasma emissivity profile as measured by the bolometric system is peaked in the plasma centre. A one dimensional Onion Skin Collisional-Radiative model (OSCR) has been developed to compute the density and radiation distributions of the main impurities. The observed centrally peaked emissivity profile can be reproduced by OSCR simulations only if finite particle confinement time and charge-exchange processes between plasma impurities and neutral hydrogen are taken into account. The neutral hydrogen density profile is computed with a recycling code. Simulations show that recycling on metal first wall such as in EXTRAP-T2R (stainless steel vacuum vessel and molybdenum limiters) is compatible with a rather high neutral hydrogen density in the plasma centre. Assuming an impurity concentration of 10% for oxygen and 3% for carbon compared with the electron density, the OSCR calculation including lines and continuum emission reproduces about 60% of the total radiated power with a similarly centrally peaked emmissivity profile. The centrally peaked emissivity profile is due to low ionisation stages and strongly radiating species in the plasma core, mainly O4+ (Be-like) and C3+ (Li-like).
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| 8. |
- Pegourie, B., et al.
(author)
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Deuterium inventory in Tore Supra : Coupled carbon-deuterium balance
- 2013
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:Suppl., s. S120-S125
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Journal article (peer-reviewed)abstract
- This paper presents an analysis of the carbon-deuterium circulation and the resulting balance in Tore Supra over the period 2002-2007. Carbon balance combines the estimation of carbon gross erosion from spectroscopy, net erosion and deposition using confocal microscopy, lock-in thermography and SEM, and a measure of the amount of deposits collected in the vacuum chamber. Fuel retention is determined from post-mortem (PM) analyses and gas balance (GB) measurements. Special attention was paid to the deuterium outgassed during the nights and weekends of the experimental campaign (vessel under vacuum, Plasma Facing Components at 120 degrees C) and during vents (vessel at atmospheric pressure, PFCs at room temperature). It is shown that this outgassing is the main process reconciling the PM and GB estimations of fuel retention, closing the coupled carbon-deuterium balance. In particular, it explains why the deuterium concentration in deposits decreases with increasing depth.
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| 9. |
- Tsitrone, E., et al.
(author)
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Multi machine scaling of fuel retention in 4 carbon dominated tokamaks
- 2011
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 415:1, s. S735-S739
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Journal article (peer-reviewed)abstract
- In order to benchmark predictions for the in vessel tritium inventory in ITER, a survey of fuel retention measured in 4 carbon dominated tokamaks (TEXTOR, ASDEX Upgrade in the 2002-2003 carbon configuration, Tore Supra and JET) was performed, showing retention rates from similar to 1 g D/h in TEXTOR (L mode, limiter machine) up to similar to 6-12 g D/h in AUG (H mode, divertor machine). A simple scaling used for ITER predictions is applied for comparison with experimental values: (1) estimate of wall fluxes, (2) estimate of the gross carbon erosion, (3) estimate of the net erosion/redeposition assuming a redeposition fraction and (4) estimate of the retention rate using D/C ratio scalings. The validity of each step is discussed, showing that this approach yields the right order of magnitude, but tends to underestimate the experimental values unless a high wall flux, a low local redeposition fraction and/or a high D/C ratio are used.
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| 10. |
- Pelicon, P., et al.
(author)
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Fuel retention study in fusion reactor walls by micro-NRA deuterium mapping
- 2011
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 269:20, s. 2317-2321
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Journal article (peer-reviewed)abstract
- Nuclear Reaction Analysis (NRA) with a (3)He ion beam is a powerful analytical technique for analysis of light elements in thin films. The main motivation for 3He focused beam applications is lateral mapping of deuterium using the nuclear reaction D((3)He,p)(4)He in surfaces exposed to a tokamak plasma, where a lateral resolution in the pm-range provides unique information for fuel retention studies. At the microprobe at the Jozef Stefan Institute typical helium ion currents of 300 pA and beam dimensions of 4 x 4 mu m(2) can be obtained. This work is focused on micro-NRA studies of plasma-facing materials using a set-up consisting of a silicon partially depleted charge particle detector for NRA spectroscopy applied in parallel with a permanently installed X-ray detector, an RBS detector and a beam chopper for ion dose monitoring. A method for absolute deuterium quantification is described. In addition, plasma-deposited amorphous deuterated carbon thin films (a-C:D) with known D content were used as a reference. The method was used to study deuterium fuel retention in carbon fibre composite materials exposed to a deuterium plasma in the Tore Supra and TEXTOR tokamaks. The high lateral resolution of micro-NRA allowed us to make a detailed study of the influence of topography on the fuel retention process. We demonstrated that the surface topography plays a dominant role in the retention of deuterium. The deep surfaces inside the castellation gaps showed approximately two orders of magnitude lower deuterium concentrations than in areas close to the exposed surface.
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| 11. |
- Petersson, Per, 1978-, et al.
(author)
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An Overview of Nuclear Microbeam Analysis of Surface and Bulk Fuel Retention in Carbon Fibre Composites from Tore Supra
- 2011
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 415:1, s. S761-S764
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Journal article (peer-reviewed)abstract
- Surface and bulk retention of deuterium in tiles of the pump limiter from Tore Supra was examined with nuclear reaction analysis using both standard and micro-beam techniques. The aim was to determine the variations in the content and distribution of fuel species in carbon-fibre composites. On plasma-facing surfaces from the deposition zone, the D content reaches 2.5 × 1019 cm−2 in about 8 μm thick top layer, but lateral differences reach even more than one order of magnitude. This is also measured in the erosion zone: 6.6 × 1017 cm−2 to 7.7 × 1018 cm−2 D atoms. Bulk content was examined on cross-sections opened by fracturing the tiles. Fuel is detected up to the depth of 1–1.5 mm beneath the plasma-facing surface in tiles from both the erosion and deposition zones. It occurs in bands, about 100 μm wide and several mm long, roughly parallel to the original plasma-facing surface.
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| 12. |
- Petersson, Per, et al.
(author)
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Micro-distribution of fuel and metal in carbon-based plasma-facing materials
- 2011
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In: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0031-8949 .- 1402-4896. ; T145, s. 014014-
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Journal article (peer-reviewed)abstract
- Surfaces of carbon fibre composite tiles from the toriodal pump limiter of Tore Supra were examined with ion beams to determine simultaneously the distribution of co-deposited deuterium and metallic plasma impurities (i. e. steel components). With a (3)He(+) ion beam the reaction (2)D((3)He, p)(4)He was used for deuterium, (12)C((3)He, p)(14)N for carbon, whereas beam-induced x-ray emission and back-scattered ions served for the detection of heavier elements. Measurements were made both with a 1mm beam and by a micro-beam focused down to 20 mu m spot size and scanned over the sample to obtain maps of the different elements. Distribution maps of different elements-fuel and metal species-are presented for four distinct regions on the limiter: erosion zone, shadowed area, thin deposits and thick flaking deposits.
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| 13. |
- Petersson, Per, 1978-, et al.
(author)
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Nuclear reaction and heavy ion ERD analysis of wall materials from controlled fusion devices : Deuterium and nitrogen-15 studies
- 2012
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 273, s. 113-117
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Journal article (peer-reviewed)abstract
- Time-of-flight HIERDA (26 MeV I-127(7+)) and micro-NRA (2.5 MeV He-3) were used to determine the composition of graphite and tungsten plasma-facing components (PFC) exposed at the TEXTOR and Tore Supra tokamaks. High sensitivity and resolution of HIERDA allowed, for the first time, for studies of nitrogen-15 showing that the gas injected during tokamak discharges is trapped on PFC, 3-7 x 10(15) N cm(-2). Also helium retention in tungsten has been identified: up to 8 x 10(15) He cm(-2). Deuterium distribution on the main limiters of Tore Supra is not uniform on tiles extracted from the erosion- and deposition-dominated areas. This is measured both on macro- (points 5 mm apart) and micro-scale (30 gm). The mapping with mu-NRA revealed the D content variation by a factor 40-50 in regions 1 x 2 mm(2): 1.2-40 x 10(17) D cm(-2) and 4-230 x 10(18) D cm(-2) in the erosion and deposition zones, respectively. In summary, the measurements of N-15 contributed to material mixing studies and improved understanding of deuterium retention on PFC.
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