| 1. |
- 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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| 2. |
- 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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| 3. |
- Neu, R., et al.
(författare)
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First operation with the JET International Thermonuclear Experimental Reactor-like wall
- 2013
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:5, s. 056111-1-056111-13
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Tidskriftsartikel (refereegranskat)abstract
- To consolidate International Thermonuclear Experimental Reactor (ITER) design choices and prepare for its operation, Joint European Torus (JET) has implemented ITER's plasma facing materials, namely, Be for the main wall and W in the divertor. In addition, protection systems, diagnostics, and the vertical stability control were upgraded and the heating capability of the neutral beams was increased to over 30 MW. First results confirm the expected benefits and the limitations of all metal plasma facing components (PFCs) but also yield understanding of operational issues directly relating to ITER. H-retention is lower by at least a factor of 10 in all operational scenarios compared to that with C PFCs. The lower C content (≈ factor 10) has led to much lower radiation during the plasma burn-through phase eliminating breakdown failures. Similarly, the intrinsic radiation observed during disruptions is very low, leading to high power loads and to a slow current quench. Massive gas injection using a D2/Ar mixture restores levels of radiation and vessel forces similar to those of mitigated disruptions with the C wall. Dedicated L-H transition experiments indicate a 30% power threshold reduction, a distinct minimum density, and a pronounced shape dependence. The L-mode density limit was found to be up to 30% higher than for C allowing stable detached divertor operation over a larger density range. Stable H-modes as well as the hybrid scenario could be re-established only when using gas puff levels of a few 1021 es-1. On average, the confinement is lower with the new PFCs, but nevertheless, H factors up to 1 (H-Mode) and 1.3 (at β N ≈ 3, hybrids) have been achieved with W concentrations well below the maximum acceptable level.
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| 4. |
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| 5. |
- Giacomelli, L., et al.
(författare)
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Neutron Emission Profiles and Energy Spectra Measurements at JET
- 2014
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Ingår i: FUSION REACTOR DIAGNOSTICS. - : AIP Publishing LLC. ; , s. 113-116
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Konferensbidrag (refereegranskat)abstract
- The joint European Torus (JET, Culham, UK) is the largest tokamak in the world. It is devoted to nuclear fusion experiments of magnetic confined Deuterium (D) or Deuterium-Tritium (DT) plasmas. JET has been upgraded over the years and recently it has also become a test facility of the components designed for ITER, the next step fusion machine under construction in Cadarache (France). JET makes use of many different diagnostics to measure the physical quantities of interest in plasma experiments. Concerning D or plasmas neutron production, various types of detectors are implemented to provide information upon the neutron total yield, emission profile and energy spectrum. The neutron emission profile emitted from the JET plasma poloidal section is reconstructed using the neutron camera (KN3). In 2010 KN3 was equipped with a new digital data acquisition system capable of high rate neutron measurements (<0.5 MCps). A similar instrument will be implemented on ITER and it is currently in its design phase. Various types of neutron spectrometers with different view lines are also operational on JET. One of them is a new compact spectrometer (KM12) based on organic liquid scintillating material which was installed in 2010 and implements a similar digital data acquisition system as for KN3. This article illustrates the measurement results of KN3 neutron emission profiles and KM 12 neutron energy spectra from the latest JET D experimental campaign C31.
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| 6. |
- Kiptily, V. G., et al.
(författare)
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Fast ions in mode conversion heating (He-3)-H plasmas in JET
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074010-
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Tidskriftsartikel (refereegranskat)abstract
- Fast ions were analysed in experiments focusing on fundamental He-3 minority and mode conversion (MC) in the ion cyclotron resonance range of frequencies (ICRF) in H plasmas and on second harmonic heating of He-3 ions at 2.65 T mimicking D-T plasma heating in ITER at half its nominal toroidal magnetic field. Gamma-ray spectrometry, neutral particle analysers and fast-ion loss diagnostics provided information on the generation of fast-ion populations and on the distribution of ICRH power among the species in various heating scenarios and for a large range of He-3 concentrations. In the scenario with the fundamental He-3 minority and MC wave heating at B-T(0) = 3.41 T and f approximate to 32 MHz, fast He-3 ions accelerated by ICRH in the MeV energy range were detected in discharges with low He-3 concentration. In the experiments with a He-3 concentration scan it was found that at a He-3 concentration of approximate to 2.2% the He-3 ion losses disappeared while a population of energetic D ions gradually built up due to a redistribution of the ICRH power between species on reaching the first MC regime. Under those conditions the ICRF-heated D beam ions effectively absorbed the wave power at their Doppler shifted resonance, which was close to the plasma centre. In discharges with second harmonic heating of He-3 ions at B-T(0) = 2.65 T and f approximate to 52 MHz, the confined energetic He-3 ions were found in the MeV energy range. There is some evidence that the D ions were also accelerated by ICRF. This paper also demonstrates that the synergy of the various fast ion diagnostics allows making a broad picture of the physics of the redistribution of the absorbed ICRH power in complicated heating scenarios of JET.
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| 7. |
- Lerche, E., et al.
(författare)
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Experimental investigation of ion cyclotron range of frequencies heating scenarios for ITER's half-field hydrogen phase performed in JET
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074008-
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Tidskriftsartikel (refereegranskat)abstract
- Two ion cyclotron range of frequencies ( ICRF) heating schemes proposed for the half-field operation phase of ITER in hydrogen plasmas-fundamental H majority and second harmonic He-3 ICRF heating-were recently investigated in JET. Although the same magnetic field and RF frequencies (f approximate to 42 MHz and f approximate to 52 MHz, respectively) were used, the density and particularly the plasma temperature were lower than those expected in the initial phase of ITER. Unlike for the well-performing H minority heating scheme to be used in He-4 plasmas, modest heating efficiencies (n = P-absorbed/P-launched < 40%) with dominant electron heating were found in both H plasma scenarios studied, and enhanced plasma-wall interaction manifested by high radiation losses and relatively large impurity content in the plasma was observed. This effect was stronger in the He-3 ICRF heating case than in the H majority heating experiments and it was verified that concentrations as high as similar to 20% are necessary to observe significant ion heating in this case. The RF acceleration of the heated ions was modest in both cases, although a small fraction of the 3He ions reached about 260 keV in the second harmonic He-3 heating experiments when 5MW of ICRF power was applied. Considerable RF acceleration of deuterium beam ions was also observed in some discharges of the He-3 heating experiments (where both the second and third harmonic ion cyclotron resonance layers of the D ions are inside the plasma) whilst it was practically absent in the majority hydrogen heating scenario. While hints of improved RF heating efficiency as a function of the plasma temperature and plasma dilution (with He-4) were confirmed in the H majority case, the He-3 concentration was the main handle on the heating efficiency in the second harmonic He-3 heating scenario.
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| 8. |
- Lerche, E., et al.
(författare)
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Optimizing ion-cyclotron resonance frequency heating for ITER : dedicated JET experiments
- 2011
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 53:12, s. 124019-
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Tidskriftsartikel (refereegranskat)abstract
- In the past years, one of the focal points of the JET experimental programme was on ion-cyclotron resonance heating (ICRH) studies in view of the design and exploitation of the ICRH system being developed for ITER. In this brief review, some of the main achievements obtained in JET in this field during the last 5 years will be summarized. The results reported here include important aspects of a more engineering nature, such as (i) the appropriate design of the RF feeding circuits for optimal load resilient operation and (ii) the test of a compact high-power density antenna array, as well as RF physics oriented studies aiming at refining the numerical models used for predicting the performance of the ICRH system in ITER. The latter include (i) experiments designed for improving the modelling of the antenna coupling resistance under various plasma conditions and (ii) the assessment of the heating performance of ICRH scenarios to be used in the non-active operation phase of ITER.
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