| 1. |
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Overview of the JET results
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:10
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Tidskriftsartikel (refereegranskat)
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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. |
- 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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| 4. |
- Batistoni, P., et al.
(författare)
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Technological exploitation of Deuterium-Tritium operations at JET in support of ITER design, operation and safety
- 2016
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 109, s. 278-285
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Tidskriftsartikel (refereegranskat)abstract
- Within the framework of the EUROfusion programme, a work-package of technology projects (WPJET3) is being carried out in conjunction with the planned Deuterium-Tritium experiment on JET (DTE2) with the objective of maximising the scientific and technological return of DT operations at JET in support of ITER. This paper presents the progress since the start of the project in 2014 in the preparatory experiments, analyses and studies in the areas of neutronics, neutron induced activation and damage in ITER materials, nuclear safety, tritium retention, permeation and outgassing, and waste production in preparation of DTE2.
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| 5. |
- Giacomelli, L., et al.
(författare)
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Neutron emission spectroscopy of DT plasmas at enhanced energy resolution with diamond detectors
- 2016
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 87:11
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Tidskriftsartikel (refereegranskat)abstract
- This work presents measurements done at the Peking University Van de Graaff neutron source of the response of single crystal synthetic diamond (SD) detectors to quasi-monoenergetic neutrons of 14-20 MeV. The results show an energy resolution of 1% for incoming 20 MeV neutrons, which, together with 1% detection efficiency, opens up to new prospects for fast ion physics studies in high performance nuclear fusion devices such as SD neutron spectrometry of deuterium-tritium plasmas heated by neutral beam injection.
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| 6. |
- Batistoni, P., et al.
(författare)
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Benchmark experiments on neutron streaming through JET Torus Hall penetrations
- 2015
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 55:5
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Tidskriftsartikel (refereegranskat)abstract
- Neutronics experiments are performed at JET for validating in a real fusion environment the neutronics codes and nuclear data applied in ITER nuclear analyses. In particular, the neutron fluence through the penetrations of the JET torus hall is measured and compared with calculations to assess the capability of state-of-art numerical tools to correctly predict the radiation streaming in the ITER biological shield penetrations up to large distances from the neutron source, in large and complex geometries. Neutron streaming experiments started in 2012 when several hundreds of very sensitive thermo-luminescence detectors (TLDs), enriched to different levels in (LiF)-Li-6/(LiF)-Li-7, were used to measure the neutron and gamma dose separately. Lessons learnt from this first experiment led to significant improvements in the experimental arrangements to reduce the effects due to directional neutron source and self-shielding of TLDs. Here we report the results of measurements performed during the 2013-2014 JET campaign. Data from new positions, at further locations in the South West labyrinth and down to the Torus Hall basement through the air duct chimney, were obtained up to about a 40m distance from the plasma neutron source. In order to avoid interference between TLDs due to self-shielding effects, only TLDs containing natural Lithium and 99.97% Li-7 were used. All TLDs were located in the centre of large polyethylene (PE) moderators, with Li-nat and Li-7 crystals evenly arranged within two PE containers, one in horizontal and the other in vertical orientation, to investigate the shadowing effect in the directional neutron field. All TLDs were calibrated in the quantities of air kerma and neutron fluence. This improved experimental arrangement led to reduced statistical spread in the experimental data. The Monte Carlo N-Particle (MCNP) code was used to calculate the air kerma due to neutrons and the neutron fluence at detector positions, using a JET model validated up to the magnetic limbs. JET biological shield and penetrations, the PE moderators and TLDs were modelled in detail. Different tallying methods were used in the calculations, which are routinely used in ITER nuclear analyses: the mesh tally and the track length estimator with multiple steps calculations using the surface source write/read capability available in MCNP. In both cases, the calculated neutron fluence (C) was compared to the measured fluence (E) and hence C/E comparisons have been obtained and are discussed. These results provide a validation of neutronics numerical tools, codes and nuclear data, used for ITER design.
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| 7. |
- Chapman, I. T., et al.
(författare)
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Advances in understanding and utilising ELM control in JET
- 2016
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- Edge localised mode (ELM) control may be essential to develop ITER scenarios with a reasonable lifetime of divertor components, whilst ELM pacing may be essential to develop stationary ITER scenarios with a tungsten divertor. Resonant magnetic perturbations (RMPs) have mitigated ELMs in high collisionality plasmas in JET. The efficacy of RMPs in mitigating the ELMs is found to depend on plasma shaping, with the change in magnetic boundary achieved when non-axisymmetric fields are applied facilitating access to small ELM regimes. The understanding of ELM pacing by vertical kicks or pellets has also been improved in a range of pedestal conditions in JET (T-ped = 0.7-1.3 keV) encompassing the ITER-expected domain (beta(N) = 1.4-2.4, H-98(y,H- 2) = 0.8-1.2, f(GW) similar to 0.7). ELM triggering is reliable provided the perturbation is above a threshold which depends on pedestal parameters. ELM triggering is achieved even in the first 10% of the natural ELM cycle suggesting no inherent maximum frequency. At high normalised pressure, the peeling-ballooning modes are stabilised as predicted by ELITE, necessitating a larger perturbation from either kicks or pellets in order to trigger ELMs. Both kicks and pellets have been used to pace ELMs for tungsten flushing. This has allowed stationary plasma conditions with low gas injection in plasmas where the natural ELM frequency is such that it would normally preclude stationary conditions.
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| 8. |
- Craciunescu, T., et al.
(författare)
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Classification of JET Neutron and Gamma Emissivity Profiles
- 2016
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Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- In thermonuclear plasmas, emission tomography uses integrated measurements along lines of sight (LOS) to determine the two-dimensional (2-D) spatial distribution of the volume emission intensity. Due to the availability of only a limited number views and to the coarse sampling of the LOS, the tomographic inversion is a limited data set problem. Several techniques have been developed for tomographic reconstruction of the 2-D gamma and neutron emissivity on JET. In specific experimental conditions the availability of LOSs is restricted to a single view. In this case an explicit reconstruction of the emissivity profile is no longer possible. However, machine learning classification methods can be used in order to derive the type of the distribution. In the present approach the classification is developed using the theory of belief functions which provide the support to fuse the results of independent clustering and supervised classification. The method allows to represent the uncertainty of the results provided by different independent techniques, to combine them and to manage possible conflicts.
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| 9. |
- Craciunescu, Teddy, et al.
(författare)
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Evaluation of reconstruction errors and identification of artefacts for JET gamma and neutron tomography
- 2016
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 87:1
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Tidskriftsartikel (refereegranskat)abstract
- The Joint European Torus (JET) neutron profile monitor ensures 2D coverage of the gamma and neutron emissive region that enables tomographic reconstruction. Due to the availability of only two projection angles and to the coarse sampling, tomographic inversion is a limited data set problem. Several techniques have been developed for tomographic reconstruction of the 2-D gamma and neutron emissivity on JET, but the problem of evaluating the errors associated with the reconstructed emissivity profile is still open. The reconstruction technique based on the maximum likelihood principle, that proved already to be a powerful tool for JET tomography, has been used to develop a method for the numerical evaluation of the statistical properties of the uncertainties in gamma and neutron emissivity reconstructions. The image covariance calculation takes into account the additional techniques introduced in the reconstruction process for tackling with the limited data set (projection resampling, smoothness regularization depending on magnetic field). The method has been validated by numerically simulations and applied to JET data. Different sources of artefacts that may significantly influence the quality of reconstructions and the accuracy of variance calculation have been identified.
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| 10. |
- Eich, T., et al.
(författare)
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ELM divertor peak energy fluence scaling to ITER with data from JET, MAST and ASDEX upgrade
- 2017
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Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 12, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- A newly established scaling of the ELM energy fluence using dedicated data sets from JET operation with CFC & ILW plasma facing components (PFCs), ASDEX Upgrade (AUG) operation with both CFC and full-W PFCs and MAST with CFC walls has been generated. The scaling reveals an approximately linear dependence of the peak ELM energy with the pedestal top electron pressure and with the minor radius; a square root dependence is seen on the relative ELM loss energy. The result of this scaling gives a range in parallel peak ELM energy fluence of 10-30 MJm(-2) for ITER Q = 10 operation and 2.5-7.5 MJm(-2) for intermediate ITER operation at 7.5 MA and 2.65 T. These latter numbers are calculated using a numerical regression (epsilon(II) = 0.28 MJ/m(2) n(e)(0.75) T-e(1) Delta E-ELM(0.5) R-1(geo)). A simple model for ELM induced thermal load is introduced, resulting in an expression for the ELM energy fluence of epsilon(II) congruent to 6 pi p(e) R-geo q(edge). The relative ELM loss energy in the data is between 2-10% and the ELM energy fluence varies within a range of 10(0.5) similar to 3 consistently for each individual device. The so far analysed power load database for ELM mitigation experiments from JET-EFCC and Kicks, MAST-RMP and AUG-RMP operation are found to be consistent with both the scaling and the introduced model, ie not showing a further reduction with respect to their pedestal pressure. The extrapolated ELM energy fluencies are compared to material limits in ITER and found to be of concern.
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| 11. |
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| 12. |
- Elevant, T., et al.
(författare)
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Profile Measurements in ITER by means of Neutron Spectroscopy, Ion Temperature Diagnostics for Experimental Thermonuclear Fusion Reactors
- 1996
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Ingår i: Workshop on diagnostics for ITER, Varenna, September 1995, proceedings of the International School of Plasma Physics, Edited by P. E. Stott et.al., Plenum Press, New York, 1996. - Boston, MA : Springer US. ; , s. 445-450
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Konferensbidrag (refereegranskat)abstract
- Information on ion temperature profiles will be needed for burn optimisation and transport studies in ITER. The feasibility of deriving these profiles for the core plasma (r< 0.75a) directly from the width of measured 14-MeV neutron energy spectra is demonstrated for Maxwellian ion distributions. Neutron energy spectra and fluxes generated under different heating conditions are calculated by means of Monte-Carlo technique. The computation takes the reaction kinematics and the velocity distributions of the reacting ions into account and calculates the resulting neutron energy distribution and flux into a defined collimator. Energy spectra of neutrons emitted along a line-of-sight are superimposed. The associated correction factor, which depends on the measured ion temperature, can be given an analytical form when fitted to code data and is insensitive to large variations in temperature-, density and magnetic flux profile shapes. The accuracy in ion temperature evaluation is expected to be better than ± 10% and can be improved to ± 5% provided information on fuel density profiles are made available.
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| 13. |
- Elevant, T., et al.
(författare)
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Role of Neutron Spectrometers for ITER
- 1998
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Ingår i: Proc. of the Int. School of Plasma Physics "Piero Calderola", Workshop on Diagnostics for Experimental Fusion Reactors, held September 4-12, 1997, in Varenna, Italy. Edited by Stott et al, Plenum Press, New York, 1998.
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Konferensbidrag (refereegranskat)abstract
- Conditions for retrieval of ion temperature profiles through measurement and evaluation of neutron energy spectra emitted in ITER-like fusion plasmas are discussed. Spectra from deuterium- and deuterium-tritium plasmas heated by 100 MW, 1 MeV neutral deuterium beams, and ignited H-mode plasmas are simulated by means of a Monte-Carlo Fokker-Planck code. Regions are defined where information on ion temperature clearly is preserved. The correction from line-of-sight integrated measurement to peak temperature is found to be 4–10% for deuterium plasmas of all temperatures and for deuterium-tritium plasmas of temperatures below approximately 5 keV. For higher temperatures the correction equals 10–30% depending on the density and temperature profiles. Ion temperatures can be determined with an accuracy better than 10% in this region only if profile data is made available.Several spectrometers have been proposed. Operating ranges in ion temperature and beam power, spatial- and temporal resolution, space requirements and life expectancy are compared with ITER measurement requirements. Necessary R&D work is also discussed.
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| 14. |
- Giegerich, T., et al.
(författare)
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Advanced design of the Mechanical Tritium Pumping System for JET DTE2
- 2016
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 109, s. 359-364
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Tidskriftsartikel (refereegranskat)abstract
- For tritium processing in JET during the next Deuterium-Tritium-Experiment (DTE2), a fully tritium compatible and continuously working vacuum pumping system has been developed. This pump train will be used as roughing pump to cover a pressure regime between 10(-1) Pa and ambient pressure. Therefore, a two-stage liquid ring pump in combination with a booster vapor diffusion pump will be applied. In this paper, a close-to-final design of the pumps is being described. Finite element (FEM) simulation results of components where high mechanical stresses due to thermal gradients are expected are presented. Furthermore, the final design of the control and data acquisition system is shown and explained.
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| 15. |
- Giegerich, Thomas, et al.
(författare)
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Conceptual design of the mechanical tritium pumping system for jet DTE2
- 2015
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Ingår i: Fusion science and technology. - : TAYLOR & FRANCIS INC. - 1536-1055 .- 1943-7641. ; 68:3, s. 630-634
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the conceptual design of the Mechanical Tritium Pumping System (MTPS) that shall be installed and tested at JET during the next Deuterium-Tritium-Experiment (DTE2). This pump train uses a two-stage liquid ring pump in combination with a booster pump to cover a pressure regime from 10(-1) Pa to 10(5) Pa. As working fluid for all pumps, mercury will be used for tritium compatibility reasons. Starting from the requirements to MTPS, the pumps and their arrangement will be described in this paper as well as the mercury containment strategy and safety- and control issues.
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| 16. |
- Hender, T. C., et al.
(författare)
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The role of MHD in causing impurity peaking in JET hybrid plasmas
- 2016
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 56:6
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Tidskriftsartikel (refereegranskat)abstract
- In hybrid plasma operation in JET with its ITER-like wall (JET-ILW) it is found that n > 1 tearing activity can significantly enhance the rate of on-axis peaking of high-Z impurities, which in turn significantly degrades discharge performance. Core n = 1 instabilities can be beneficial in removing impurities from the plasma core (e.g. sawteeth or fishbones), but can conversely also degrade core confinement (particularly in combination with simultaneous n = 3 activity). The nature of magnetohydrodynamic instabilities in JET hybrid discharges, with both its previous carbon wall and subsequent JET-ILW, is surveyed statistically and the character of the instabilities is examined. Possible qualitative models for how the n > 1 islands can enhance the on-axis impurity transport accumulation processes are presented.
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| 17. |
- Loarer, T., et al.
(författare)
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Plasma isotopic changeover experiments in JET under carbon and ITER-like wall conditions
- 2015
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 55:4
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Tidskriftsartikel (refereegranskat)abstract
- In JET-ILWisotopic plasma wall changeover experiments have been carried out to determine the amount of particles accessible by changing the plasma from H to D and from D to H. The gas balance analysis integrated over the experimental sessions show that the total amount of H or D removed from the wall is in the range of (1-3) x 10(22)D. For both changeover experiments, the respective plasma isotopic ratio behaviour is exactly the same as a function of the pulse number. After only 80 s of plasma (4 pulses), the plasma isotopic ratio is lower than 10%, below 4.5% after 13 pulses and then saturates around similar to 2-3%. In these conditions, the removal efficiency through plasma operation becomes very poor. The saturation of the plasma isotopic ratio in the range of 10% is also observed for the JET-C configuration although the amount of tritium retained in the vessel after the DT pulses was more than one order of magnitude compared to the retention observed with the JET-ILW. This demonstrates that the amount of particle recovery through plasma changeover is independent from the long term retention. Since this long term reservoir results from codeposition, these experiments suggest that there is a limited access to these codeposited particles by plasma isotopic changeover. Finally, in ITER, change over from D/T to H at the end of the discharge for possibly reducing the long term retention does not appear as a good strategy.
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| 18. |
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| 19. |
- Nakano, T., et al.
(författare)
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Determination of tungsten and molybdenum concentrations from an x-ray range spectrum in JET with the ITER-like wall configuration
- 2015
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Ingår i: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 48:14
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Tidskriftsartikel (refereegranskat)abstract
- The W45+ and W46+ 3p-4d inner shell excitation lines in addition to Mo32+ 2p-3s lines have been identified from the spectrum taken by an upgraded high-resolution x-ray spectrometer. It is found from analysis of the absolute intensities of the W46+ and Mo32+ lines that W and Mo concentrations are in the range of similar to 10(-5) and similar to 10(-6), respectively, with a ratio of similar to 5% in JET with the ITER-like wall configuration for ELMy H-mode plasmas with a plasma current of 2.0-2.5 MA, a toroidal magnetic field of 2.7 T and a neutral beam injection power of 14-18 MW. For the purpose of checking self-consistency, it is confirmed that the W concentration determined from the W45+ line is in agreement with that from the W46+ line within 20% and that the plasma effective charge determined from the continuum of the first order reflection spectrum is also in agreement with that from the second order within 50%. Further, the determined plasma effective charge is in agreement with that determined from a visible spectroscopy, confirming that the sensitivity of the x-ray spectrometer is valid and that the W and the Mo concentrations are also likely to be valid.
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| 20. |
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| 21. |
- Vasilopoulou, T., et al.
(författare)
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Neutron streaming along ducts and labyrinths at the JET biological shielding : Effect of concrete composition
- 2015
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Ingår i: Radiation Physics and Chemistry. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0969-806X .- 1879-0895. ; 116, s. 359-364
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Tidskriftsartikel (refereegranskat)abstract
- Experiments and Monte Carlo simulations were performed at the Joint European Torus (JET) in order to validate the computational tools and methods applied for neutron streaming calculations through penetrations in the JET Hall biological shielding. In the present work the sensitivity of the simulations on the hydrogen and boron content in concrete shielding was investigated. MCNP code was used to simulate neutron streaming along the JET Hall personnel entrance labyrinth for deuterium-deuterium and deuterium-tritium plasma sources for different concrete wall compositions. Neutron fluence and ambient dose equivalent along the labyrinth were calculated. Simulation results for the "as built" JET concrete composition were compared against measurements performed using thermoluminescence detectors. This study contributes to the optimization of the radiation shielding of JET and, furthermore, provides information from JET experience that may assist in optimizing and validating the radiation shielding design methodology used in its successor fusion devices ITER and DEMO.
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