| 341. |
- Uccello, Andrea, et al.
(author)
-
Comparison of dust transport modelling codes in a tokamak plasma
- 2016
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In: Physics of Plasmas. - : AMER INST PHYSICS. - 1070-664X .- 1089-7674. ; 23:10
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Journal article (peer-reviewed)abstract
- Since the installation on the Joint European Torus of the ITER-like Wall (ILW), intense radiation spikes have been observed, especially in the discharges following a disruption, and have been associated with possible sudden injection of tungsten (W) impurities consequent to full ablation of W dust particles. The problem of dust production, mobilization, and interaction both with the plasma and the vessel tiles is therefore of great concern and requires the setting up of dedicated and validated numerical modeling tools. Among these, a useful role is played by the dust trajectory calculators, which can present in a relatively clear way the qualitative and quantitative description of the mobilization and fate of selected bunches of dust grains.
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| 342. |
- Uljanovs, J., et al.
(author)
-
The isotope effect on divertor conditions and neutral pumping in horizontal divertor configurations in JET-ILW Ohmic plasmas
- 2017
-
In: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 12, s. 791-797
-
Journal article (peer-reviewed)abstract
- Understanding the impact of isotope mass and divertor configuration on the divertor conditions and neutral pressures is critical for predicting the performance of the ITER divertor in DT operation. To address this need, ohmically heated hydrogen and deuterium plasma experiments were conducted in JET with the ITER-like wall in varying divertor configurations. In this study, these plasmas are simulated with EDGE2D-EIRENE outfitted with a sub-divertor model, to predict the neutral pressures in the plenum with similar fashion to the experiments. EDGE2D-EIRENE predictions show that the increased isotope mass results in up to a 25% increase in peak electron densities and 15% increase in peak ion saturation current at the outer target in deuterium when compared to hydrogen for all horizontal divertor configurations. Indicating that a change from hydrogen to deuterium as main fuel decreases the neutral mean free path, leading to higher neutral density in the divertor. Consequently, this mechanism also leads to higher neutral pressures in the sub-divertor. The experimental data provided by the hydrogen and deuterium ohmic discharges shows that closer proximity of the outer strike point to the pumping plenum results in a higher neutral pressure in the sub-divertor. The diaphragm capacitance gauge pressure measurements show that a two to three-fold increase in sub-divertor pressure was achieved in the corner and nearby horizontal configurations compared to the far-horizontal configurations, likely due to ballistic transport (with respect to the plasma facing components) of the neutrals into the sub-divertor. The corner divertor configuration also indicates that a neutral expansion occurs during detachment, resulting in a sub-divertor neutral density plateau as a function of upstream density at the outer-mid plane.
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| 343. |
- van Milligen, B. Ph, et al.
(author)
-
Radial variation of heat transport in L-mode JET discharges
- 2019
-
In: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 59:5
-
Journal article (peer-reviewed)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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| 344. |
- Varje, J., et al.
(author)
-
Synthetic diagnostic for the JET scintillator probe lost alpha measurements
- 2019
-
In: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 14
-
Journal article (peer-reviewed)abstract
- A synthetic diagnostic has been developed for the JET lost alpha scintillator probe, based on the ASCOT fast ion orbit following code and the AFSI fusion source code. The synthetic diagnostic models the velocity space distribution of lost fusion products in the scintillator probe. Validation with experimental measurements is presented, where the synthetic diagnostic is shown to predict the gyroradius and pitch angle of lost DD protons and tritons. Additionally, the synthetic diagnostic reproduces relative differences in total loss rates in multiple phases of the discharge, which can be used as a basis for total loss rate predictions.
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| 345. |
- Varje, J., et al.
(author)
-
Synthetic NPA diagnostic for energetic particles in JET plasmas
- 2017
-
In: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12
-
Journal article (peer-reviewed)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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| 346. |
- Vasilopoulou, T., et al.
(author)
-
Improved neutron activation dosimetry for fusion
- 2019
-
In: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 139, s. 109-114
-
Journal article (peer-reviewed)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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| 347. |
- Vasilopoulou, T., et al.
(author)
-
Neutron streaming along ducts and labyrinths at the JET biological shielding : Effect of concrete composition
- 2015
-
In: Radiation Physics and Chemistry. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0969-806X .- 1879-0895. ; 116, s. 359-364
-
Journal article (peer-reviewed)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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| 348. |
- Vega, J., et al.
(author)
-
Real-time implementation with FPGA-based DAQ system of a probabilistic disruption predictor from scratch
- 2018
-
In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 129, s. 179-182
-
Journal article (peer-reviewed)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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| 349. |
- Villari, R., et al.
(author)
-
ITER oriented neutronics benchmark experiments on neutron streaming and shutdown dose rate at JET
- 2017
-
In: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 123, s. 171-176
-
Journal article (peer-reviewed)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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| 350. |
- Villari, R., et al.
(author)
-
Neutronics experiments and analyses in preparation of DT operations at JET
- 2016
-
In: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 109, s. 895-905
-
Journal article (peer-reviewed)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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