| 271. |
- van Milligen, B. Ph, et al.
(författare)
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Radial variation of heat transport in L-mode JET discharges
- 2019
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Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 59:5
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze heat transport in the JET tokamak using data from its high resolution ECE diagnostic and analyses based on the transfer entropy (TE). The analysis reveals that heat transport is not smooth and continuous, but is characterized by 'trapping regions' separated by `minor transport barriers'. Meat may 'jump over' these barriers and when the heating power is raised, this 'jumping' behavior becomes more prominent. To check that our results are relevant for global heat transport, we deduced an effective diffusion coefficient from the TE results. Both its value and overall radial variation are consistent with heat diffusivities reported in literature. The detailed radial structure of the effective diffusion coefficient was shown to be linked to the mentioned minor transport barriers.
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| 272. |
- Varje, J., et al.
(författare)
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Synthetic NPA diagnostic for energetic particles in JET plasmas
- 2017
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221 .- 1748-0221. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Neutral particle analysis (NPA) is one of the few methods for diagnosing fast ions inside a plasma by measuring neutral atom fluxes emitted due to charge exchange reactions. The JET tokamak features an NPA diagnostic which measures neutral atom fluxes and energy spectra simultaneously for hydrogen, deuterium and tritium species. A synthetic NPA diagnostic has been developed and used to interpret these measurements to diagnose energetic particles in JET plasmas with neutral beam injection (NBI) heating. The synthetic NPA diagnostic performs a Monte Carlo calculation of the neutral atom fluxes in a realistic geometry. The 4D fast ion distributions, representing NBI ions, were simulated using the Monte Carlo orbit-following code ASCOT. Neutral atom density profiles were calculated using the FRANTIC neutral code in the JINTRAC modelling suite. Additionally, for rapid analysis, a scan of neutral profiles was precalculated with FRANTIC for a range of typical plasma parameters. These were taken from the JETPEAK database, which includes a comprehensive set of data from the flat-top phases of nearly all discharges in recent JET campaigns. The synthetic diagnostic was applied to various JET plasmas in the recent hydrogen campaign where different hydrogen/deuterium mixtures and NBI configurations were used. The simulated neutral fluxes from the fast ion distributions were found to agree with the measured fluxes, reproducing the slowing-down profiles for different beam isotopes and energies and quantitatively estimating the fraction of hydrogen and deuterium fast ions.
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| 273. |
- Vasilopoulou, T., et al.
(författare)
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Improved neutron activation dosimetry for fusion
- 2019
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 139, s. 109-114
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Tidskriftsartikel (refereegranskat)abstract
- Neutron activation technique has been widely used for the monitoring of neutron fluence at the Joint European Torus (JET) whereas it is foreseen to be employed at future fusion plants, such as ITER and DEMO. Neutron activation provides a robust tool for the measurement of neutron fluence in the complex environment encountered in a tokamak. However, activation experiments previously performed at JET showed that the activation foils used need to be calibrated in a real fusion environment in order to provide accurate neutron fluence data. Triggered by this challenge, an improved neutron activation method for the evaluation of neutron fluence at fusion devices has been developed. Activation assemblies similar to those used at JET were irradiated under 14 MeV neutrons at the Frascati Neutron Generator (FNG) reference neutron field. The data obtained from the calibration experiment were applied for the analysis of activation foil measurements performed during the implemented JET Deuterium-Deuterium (D-D) campaign. The activation results were compared against thermoluminescence measurements and a satisfactory agreement was observed. The proposed method provides confidence on the use of activation technique for the precise estimation of neutron fluence at fusion devices and enables its successful implementation in the forthcoming JET Deuterium-Tritium (D-T) campaign.
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| 274. |
- Vega, J., et al.
(författare)
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Real-time implementation with FPGA-based DAQ system of a probabilistic disruption predictor from scratch
- 2018
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Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 129, s. 179-182
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Tidskriftsartikel (refereegranskat)abstract
- Real-time (RT) disruption prediction (DP) is essential to trigger mitigation actions that avoid irreversible damage to the devices. This paper deals with disruption mitigation alarms and performs the RT implementation of a probabilistic predictor. The RT implementation has been carried out with a fast controller with DAQ FPGA-based data acquisition devices corresponding to ITER catalogue (in particular, a reconfigurable Input/Output platform has been used). Up to three input signals have been used and relevant information for the prediction is extracted from the temporal and the frequency domains. The signals are read from the JET database. Then D/A conversions are carried out and used as inputs to the real time system. In this way, the whole process of digitization, data analysis and prediction is performed. The computation time for each prediction takes less than 200 mu s.
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| 275. |
- Villari, R., et al.
(författare)
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ITER oriented neutronics benchmark experiments on neutron streaming and shutdown dose rate at JET
- 2017
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 123, s. 171-176
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Tidskriftsartikel (refereegranskat)abstract
- Neutronics benchmark experiments are conducted at JET in the frame of WPJET3 NEXP within EUROfusion Consortium for validating the neutronics codes and tools used in ITER nuclear analyses to predict quantities such as the neutron flux along streaming paths and dose rates at the shutdown due to activated components. The preparation of neutron streaming and shutdown dose rate experiments for the future Deuterium-Tritium operations (DTE2 campaign) are in progress. This paper summarizes the status of measurements and analyses in progress in the current Deuterium-Deuterium (DD) campaign and the efforts in preparation for DTE2.
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| 276. |
- Villari, R., et al.
(författare)
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Neutronics experiments and analyses in preparation of DT operations at JET
- 2016
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 109, s. 895-905
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Tidskriftsartikel (refereegranskat)abstract
- In the frame of the WPJET3-DT Technology project within the EUROfusion Consortium program, neutronics experiments are in preparation for the future deuterium-tritium campaign on JET (DTE2). The experiments will be conducted with the purpose to validate the neutronics codes and tools used in ITER, thus reducing the related uncertainties and the associated risks in the machine operation. This paper summarizes the status of previous shutdown dose rate benchmarks experiments and analyses performed at JET and focuses on the computational and experimental efforts conducted in preparation of the future DTE2 experiments. In particular, preliminary calculations and studies to select detectors and positions aimed to reduce uncertainties in the shutdown dose rate experiment are presented and discussed.
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| 277. |
- Villari, R., et al.
(författare)
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Shutdown dose rate neutronics experiment during high performances DD operations at JET
- 2018
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Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 136, s. 1545-1549
-
Tidskriftsartikel (refereegranskat)abstract
- A novel Shutdown dose rate benchmark experiment has been performed at Joint European Torus (JET) machine during the last high performance Deuterium-Deuterium (DD) campaign in preparation of future high Deuterium Tritium experiment (DTE2). On-line continuous gamma dose rate measurements were performed for four months at two ITER relevant ex-vessel positions close to Radial Neutron Camera and on the top of ITER-like Antenna using high-sensitive ionization chambers. Decay gamma spectra at the shutdown were also collected using High Purity Germanium spectrometer to identify dominant radionuclides contributing to the dose. Neutron fluence measurements during operations were performed as well using activation foils assembly installed close to ionization chambers. The measurements are performed to validate shutdown dose rate tools used in ITER. This paper presents the experimental assembly and measurements analyses.
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| 278. |
- Viola, B., et al.
(författare)
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EDGE2D-EIRENE simulations of the impact of poloidal flux expansion on the radiative divertor performance in JET
- 2017
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Ingår i: Nuclear Materials and Energy. - : ELSEVIER. - 2352-1791. ; 12, s. 786-790
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Tidskriftsartikel (refereegranskat)abstract
- In the past at JET, with the MkI divertor, a systematic study of the influence of X-point height and poloidal flux expansion has been conducted [1,2] showing minor differences in the radiation distribution, whereas in [3] experiment and simulations have shown enhancement of detachment as the flux expansion was increased. More recently at JET, equipped with the ITER-like wall (ILW), radiative seeded scenarios have been studied and a maximum radiation fraction 75% has been achieved. EDGE2D-EIRENE [4-6] simulations [7,8] have already shown that the divertor heat fluxes can be reduced with N2 injection, qualitatively consistent with experimental observations [9], by adjusting the impurity injection rate to reproduce the measured divertor radiation. In this paper we will present edge predictive simulations on the assessment of effects of poloidal flux expansion and recycling on radiation distribution and X-point peaking on JET-ILW nitrogen seeded plasmas.
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| 279. |
- Wiesen, S., et al.
(författare)
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Effect of PFC Recycling Conditions on JET Pedestal Density
- 2016
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 56:6-8, s. 754-759
-
Tidskriftsartikel (refereegranskat)abstract
- There is experimental evidence that the pedestal dynamics in type-I ELMy H-mode discharges is significantly affected by a change in the recycling conditions at the tungsten plasma-facing components (W-PFCs) after an ELM event. The integrated code JINTRAC has been employed to assess the impact of recycling conditions during type-I ELMs in JET ITER-like wall H-mode discharges. By employing a heuristic approach, a model to mimic the physical processes leading to formation and release (i.e. outgassing) of finite near-surface fuel reservoirs in W-PFCs has been implemented into the EDGE2D-EIRENE plasma-wall interaction code being part of JINTRAC. As main result it is shown, that a delay in the density pedestal build-up after an ELM event can be provoked by reduced recycling induced by depleted W-PFC particle near-surface reservoirs. However the pedestal temperature evolution is barely affected by the change in recycling parameters suggesting that the presented model is incomplete.
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| 280. |
- Wiesen, S., et al.
(författare)
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Modelling of plasma-edge and plasma-wall interaction physics at JET with the metallic first-wall
- 2016
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T167
-
Tidskriftsartikel (refereegranskat)abstract
- An overview is given on the recent progress on edge modelling activities for the JET ITER-like wall using the computational tools like the SOLPS or EDGE2D-EIRENE code. The validation process of these codes on JET with its metallic plasma-facing components is an important step towards predictive studies for ITER and DEMO in relevant divertor operational conditions, i.e., for detached, radiating divertors. With increased quantitative credibility in such codes more reliable input to plasma-wall and plasma-material codes can be warranted, which in turn results in more realistic and physically sound estimates of the life-time expectations and performance of a Be first-wall and a W-divertor, the same materials configuration foreseen for ITER. A brief review is given on the recent achievements in the plasma-wall interaction and material migration studies. Finally, a short summary is given on the availability and development of integrated codes to assess the performance of an JET-ILW baseline scenario also in view of the preparation for a JET DT-campaign.
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