| 1. |
- Aho-Mantila, L., et al.
(författare)
-
Assessment of SOLPS5.0 divertor solutions with drifts and currents against L-mode experiments in ASDEX Upgrade and JET
- 2017
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 59:3
-
Tidskriftsartikel (refereegranskat)abstract
- The divertor solutions obtained with the plasma edge modelling tool SOLPS5.0 are discussed. The code results are benchmarked against carefully analysed L-mode discharges at various density levels with and without impurity seeding in the full-metal tokamaks ASDEX Upgrade and JET. The role of the cross-field drifts and currents in the solutions is analysed in detail, and the improvements achieved by fully activating the drift and current terms in view of matching the experimental signals are addressed. The persisting discrepancies are also discussed.
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| 2. |
- Aiba, N., et al.
(författare)
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Numerical analysis of ELM stability with rotation and ion diamagnetic drift effects in JET
- 2017
-
Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:12
-
Tidskriftsartikel (refereegranskat)abstract
- Stability to the type-I edge localized mode (ELM) in JET plasmas was investigated numerically by analyzing the stability to a peeling-ballooning mode with the effects of plasma rotation and ion diamagnetic drift. The numerical analysis was performed by solving the extended Frieman-Rotenberg equation with the MINERVA-DI code. To take into account these effects in the stability analysis self-consistently, the procedure of JET equilibrium reconstruction was updated to include the profiles of ion temperature and toroidal rotation, which are determined based on the measurement data in experiments. With the new procedure and MINERVA-DI, it was identified that the stability analysis including the rotation effect can explain the ELM trigger condition in JET with ITER like wall (JET-ILW), though the stability in JET with carbon wall (JET-C) is hardly affected by rotation. The key difference is that the rotation shear in JET-ILW plasmas analyzed in this study is larger than that in JET-C ones, the shear which enhances the dynamic pressure destabilizing a peeling-ballooning mode. In addition, the increase of the toroidal mode number of the unstable MHD mode determining the ELM trigger condition is also important when the plasma density is high in JET-ILW. Though such modes with high toroidal mode number are strongly stabilized by the ion diamagnetic drift effect, it was found that plasma rotation can sometimes overcome this stabilizing effect and destabilizes the peeling-ballooning modes in JET-ILW.
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| 3. |
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| 4. |
- Andersson Sundén, Erik, et al.
(författare)
-
An assessment of nitrogen concentrations from spectroscopic measurements in the JET and ASDEX upgrade divertor
- 2019
-
Ingår i: Nuclear Materials and Energy. - : Elsevier. - 2352-1791. ; 18, s. 147-152
-
Tidskriftsartikel (refereegranskat)abstract
- The impurity concentration in the tokamak divertor plasma is a necessary input for predictive scaling of divertor detachment, however direct measurements from existing tokamaks in different divertor plasma conditions are limited. To address this, we have applied a recently developed spectroscopic N II line ratio technique for measuring the N concentration in the divertor to a range of H-mode and L-mode plasma from the ASDEX Upgrade and JET tokamaks, respectively. The results from both devices show that as the power crossing the separatrix, P-sep, is increased under otherwise similar core conditions (e.g. density), a higher N concentration is required to achieve the same detachment state. For example, the N concentrations at the start of detachment increase from approximate to 2% to approximate to 9% as P-sep, is increased from approximate to 2.5 MW to approximate to 7 MW. These results tentatively agree with scaling law predictions (e.g. Goldston et al.) motivating a further study examining the parameters which affect the N concentration required to reach detachment. Finally, the N concentrations from spectroscopy and the ratio of D and N gas valve fluxes agree within experimental uncertainty only when the vessel surfaces are fully-loaded with N.
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| 5. |
- Angioni, C., et al.
(författare)
-
Gyrokinetic study of turbulent convection of heavy impurities in tokamak plasmas at comparable ion and electron heat fluxes
- 2017
-
Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 57:2
-
Tidskriftsartikel (refereegranskat)abstract
- In tokamaks, the role of turbulent transport of heavy impurities, relative to that of neoclassical transport, increases with increasing size of the plasma, as clarified by means of general scalings, which use the ITER standard scenario parameters as reference, and by actual results from a selection of discharges from ASDEX Upgrade and JET. This motivates the theoretical investigation of the properties of the turbulent convection of heavy impurities by nonlinear gyrokinetic simulations in the experimentally relevant conditions of comparable ion and electron heat fluxes. These conditions also correspond to an intermediate regime between dominant ion temperature gradient turbulence and trapped electron mode turbulence. At moderate plasma toroidal rotation, the turbulent convection of heavy impurities, computed with nonlinear gyrokinetic simulations, is found to be directed outward, in contrast to that obtained by quasi-linear calculations based on the most unstable linear mode, which is directed inward. In this mixed turbulence regime, with comparable electron and ion heat fluxes, the nonlinear results of the impurity transport can be explained by the coexistence of both ion temperature gradient and trapped electron modes in the turbulent state, both contributing to the turbulent convection and diffusion of the impurity. The impact of toroidal rotation on the turbulent convection is also clarified.
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| 6. |
- Angioni, C., et al.
(författare)
-
The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas
- 2015
-
Ingår i: Physics of Plasmas. - : AMER INST PHYSICS. - 1070-664X .- 1089-7674. ; 22:5
-
Tidskriftsartikel (refereegranskat)abstract
- Recent progress in the understanding and prediction of the tungsten behaviour in the core of JET H-mode plasmas with ITER-like wall is presented. Particular emphasis is given to the impact of poloidal asymmetries of the impurity density. In particular, it is shown that the predicted reduction of temperature screening induced by the presence of low field side localization of the tungsten density produced by the centrifugal force is consistent with the observed tungsten behaviour in a JET discharge in H-mode baseline scenario. This provides first evidence of the role of poloidal asymmetries in reducing the strength of temperature screening. The main differences between plasma parameters in JET baseline and hybrid scenario discharges which affect the impact of poloidally asymmetric density on the tungsten radial transport are identified. This allows the conditions by which tungsten accumulation can be avoided to be more precisely defined.
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| 7. |
- Appel, L. C., et al.
(författare)
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Equilibrium reconstruction in an iron core tokamak using a deterministic magnetisation model
- 2018
-
Ingår i: Computer Physics Communications. - : ELSEVIER. - 0010-4655 .- 1879-2944. ; 223, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- In many tokamaks ferromagnetic material, usually referred to as an iron-core, is present in order to improve the magnetic coupling between the solenoid and the plasma. The presence of the iron core in proximity to the plasma changes the magnetic topology with consequent effects on the magnetic field structure and the plasma boundary. This paper considers the problem of obtaining the free-boundary plasma equilibrium solution in the presence of ferromagnetic material based on measured constraints. The current approach employs, a model described by O'Brien et al. (1992) in which the magnetisation currents at the iron-air boundary are represented by a set of free parameters and appropriate boundary conditions are enforced via a set of quasi-measurements on the material boundary. This can lead to the possibility of overfitting the data and hiding underlying issues with the measured signals. Although the model typically achieves good fits to measured magnetic signals there are significant discrepancies in the inferred magnetic topology compared with other plasma diagnostic measurements that are independent of the magnetic field. An alternative approach for equilibrium reconstruction in iron-core tokamaks, termed the deterministic magnetisation model is developed and implemented in EFIT++. The iron is represented by a boundary current with the gradients in the magnetisation dipole state generating macroscopic internal magnetisation currents. A model for the boundary magnetisation currents at the iron-air interface is developed using B-Splines enabling continuity to arbitrary order; internal magnetisation currents are allocated to triangulated regions within the iron, and a method to enable adaptive refinement is implemented. The deterministic model has been validated by comparing it with a synthetic 2-D electromagnetic model of JET. It is established that the maximum field discrepancy is less than 1.5 mT throughout the vacuum region enclosing the plasma. The discrepancies of simulated magnetic probe signals are accurate to within 1% for signals with absolute magnitude greater than 100 mT; in all other cases agreement is to within 1 mT. The effect of neglecting the internal magnetisation currents increases the maximum discrepancy in the vacuum region to >20 mT, resulting in errors of 5%-10% in the simulated probe signals. The fact that the previous model neglects the internal magnetisation currents (and also has additional free parameters when fitting the measured data) makes it unsuitable for analysing data in the absence of plasma current. The discrepancy of the poloidal magnetic flux within the vacuum vessel is to within 0.1 Wb. Finally the deterministic model is applied to an equilibrium force-balance solution of a JET discharge using experimental data. It is shown that the discrepancies of the outboard separatrix position, and the outer strike-point position inferred from Thomson Scattering and Infrared camera data are much improved beyond the routine equilibrium reconstruction, whereas the discrepancy of the inner strike-point position is similar.
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| 8. |
- Arnichand, H., et al.
(författare)
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Discriminating the trapped electron modes contribution in density fluctuation spectra
- 2015
-
Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 55:9
-
Tidskriftsartikel (refereegranskat)abstract
- Quasi-coherent (QC) modes have been reported for more than 10 years in reflectometry fluctuations spectra in the core region of fusion plasmas. They have characteristics in-between coherent and broadband fluctuations as they oscillate at a marked frequency but have a wide spectrum. This work presents further evidences of the link recently established between QC modes and the trapped electron modes (TEM) instabilities (Arnichand et al 2014 Nucl. Fusion 54 123017). In electron cyclotron resonance heated discharges of Tore Supra, an enhancement of QC modes amplitude is observed in a region where TEM cause impurity transport and turbulence. In JET Ohmic plasmas, QC modes disappear during density ramp-up and current ramp-down. This is reminiscent of Tore Supra and TEXTOR observations during transitions from the linear Ohmic confinement (LOC) to the saturated Ohmic confinement (SOC) regimes. Evidencing TEM activity then becomes experimentally possible via analysis of fluctuation spectra.
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| 9. |
- Baiocchi, B., et al.
(författare)
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Transport analysis and modelling of the evolution of hollow density profiles plasmas in JET and implication for ITER
- 2015
-
Ingår i: Nuclear Fusion. - : IOP PUBLISHING LTD. - 0029-5515 .- 1741-4326. ; 55:12
-
Tidskriftsartikel (refereegranskat)abstract
- The density evolution during the transient phase just after the L-H transition is investigated using theoretical transport models. Cases characterized by core densities which evolve in longer timescales than the edge densities, leading to hollow density profiles (R/L-n = -R del n/n < 0) are modelled. This density evolution is particularly interesting because it has been shown to be beneficial in the view of the access to burning plasma conditions in ITER (Loarte et al 2013 Nucl. Fusion 53 083031). Self-consistent simulations of the JET discharge 79676 of the density-only, and of the density and the temperatures are carried out using a quasilinear gyrokinetic code, QuaLiKiz (Bourdelle et al 2007 Phys. Plasmas 14 112501), coupled with a transport code CRONOS (Artaud et al 2010 Nucl. Fusion 50 043001). The slow evolution of the hollow density, associated with the self-consistently calculated hollow NBI particle deposition, is well reproduced in the plasma core. Indeed, QuaLiKiz is shown to reproduce nonlinear gyrokinetic heat and particle fluxes well for both positive and negative R/L-n. That gives a theoretical and general basis for the persistence of the hollowness, laying the groundwork for the extrapolation to ITER.
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| 10. |
- Baiocchi, B., et al.
(författare)
-
Turbulent transport analysis of JET H-mode and hybrid plasmas using QuaLiKiz and Trapped Gyro Landau Fluid
- 2015
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 57:3
-
Tidskriftsartikel (refereegranskat)abstract
- The physical transport processes at the basis of JET typical inductive H-mode scenarios and advanced hybrid regimes, with improved thermal confinement, are analyzed by means of some of the newest and more sophisticated quasi-linear transport models: trapped gyro Landau fluid (TGLF) and QuaLiKiz. The temporal evolution of JET pulses is modelled by CRONOS where the turbulent transport is modelled by either QuaLiKiz or TGLF. Both are first principle models with a more comprehensive physics than the models previously developed and therefore allow the analysis of the physics at the basis of the investigated scenarios. For H-modes, ion temperature gradient (ITG) modes are found to be dominant and the transport models are able to properly reproduce temperature profiles in self-consistent simulations. However, for hybrid regimes, in addition to ITG trapped electron modes (TEM) are also found to be important and different physical mechanisms for turbulence reduction play a decisive role. Whereas E x B flow shear and plasma geometry have a limited impact on turbulence, the presence of a large population of fast ions, quite important in low density regimes, can stabilize core turbulence mainly when the electromagnetic effects are taken into account. The TGLF transport model properly captures these mechanisms and correctly reproduces temperatures.
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| 11. |
- Baron-Wiechec, A., et al.
(författare)
-
First dust study in JET with the ITER-like wall : sampling, analysis and classification
- 2015
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:11
-
Tidskriftsartikel (refereegranskat)abstract
- Results of the first dust survey in JET with the ITER-Like Wall (JET-ILW) are presented. The sampling was performed using adhesive stickers from the divertor tiles where the greatest material deposition was detected after the first JET-ILW campaign in 2011-2012. The emphasis was especially on sampling and analysis of metal particles (Be and W) with the aim to determine the composition, size, surface topography and internal dust structure using a large set of methods: high-resolution scanning and transmission electron microscopy, focused ion beam, electron diffraction and also wavelength and energy dispersive x-ray spectroscopy. The most important was the identification of beryllium dust both in the form of flakes and droplets with dimensions in the micrometer range. Tungsten, molybdenum, inconel constituents were identified along with many impurity species. The particles are categorised and the origin of the various constituents discussed.
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| 12. |
- Basiuk, V., et al.
(författare)
-
Towards self-consistent plasma modelisation in presence of neoclassical tearing mode and sawteeth : effects on transport coefficients
- 2017
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 59:12
-
Tidskriftsartikel (refereegranskat)abstract
- The neoclassical tearing modes (NTM) increase the effective heat and particle radial transport inside the plasma, leading to a flattening of the electron and ion temperature and density profiles at a given location depending on the safety factor q rational surface (Hegna and Callen 1997 Phys. Plasmas 4 2940). In burning plasma such as in ITER, this NTM-induced increased transport could reduce significantly the fusion performance and even lead to a disruption. Validating models describing the NTM-induced transport in present experiment is thus important to help quantifying this effect on future devices. In this work, we apply an NTM model to an integrated simulation of current, heat and particle transport on JET discharges using the European transport simulator. In this model, the heat and particle radial transport coefficients are modified by a Gaussian function locally centered at the NTM position and characterized by a full width proportional to the island size through a constant parameter adapted to obtain the best simulations of experimental profiles. In the simulation, the NTM model is turned on at the same time as the mode is triggered in the experiment. The island evolution is itself determined by the modified Rutherford equation, using self-consistent plasma parameters determined by the transport evolution. The achieved simulation reproduces the experimental measurements within the error bars, before and during the NTM. A small discrepancy is observed on the radial location of the island due to a shift of the position of the computed q = 3/2 surface compared to the experimental one. To explain such small shift (up to about 12% with respect to the position observed from the experimental electron temperature profiles), sensitivity studies of the NTM location as a function of the initialization parameters are presented. First results validate both the transport model and the transport modification calculated by the NTM model.
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| 13. |
- Batistoni, P., et al.
(författare)
-
Technical preparations for the in-vessel 14 MeV neutron calibration at JET
- 2017
-
Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 117, s. 107-114
-
Tidskriftsartikel (refereegranskat)abstract
- The power output of fusion devices is measured from their neutron yields which relate directly to the fusion yield. In this paper we describe the devices and methods that have been prepared to perform a new in situ 14 MeV neutron calibration at JET in view of the new DT campaign planned at JET in the next years. The target accuracy of this calibration is 10% as required for ITER, where a precise neutron yield measurement is important, e.g., for tritium accountancy. In this paper, the constraints and early decisions which defined the main calibration approach are discussed, e.g., the choice of 14 MeV neutron source and the deployment method. The physics preparations, source issues, safety and engineering aspects required to calibrate directly the JET neutron detectors are also discussed. The existing JET remote-handling system will be used to deploy the neutron source inside the JET vessel. For this purpose, compatible tooling and systems necessary to ensure safe and efficient deployment have been developed. The scientific programme of the preparatory phase is devoted to fully characterizing the selected 14 MeV neutron generator to be used as the calibrating source, obtain a better understanding of the limitations of the calibration, optimise the measurements and other provisions, and to provide corrections for perturbing factors (e.g., anisotropy of the neutron generator, neutron energy spectrum dependence on emission angle). Much of this work has been based on an extensive programme of Monte-Carlo calculations which provide support and guidance in developing the calibration strategy.
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| 14. |
- Beal, J., et al.
(författare)
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Deposition in the inner and outer corners of the JET divertor with carbon wall and metallic ITER-like wall
- 2016
-
Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T167
-
Tidskriftsartikel (refereegranskat)abstract
- Rotating collectors and quartz microbalances (QMBs) are used in JET to provide time-dependent measurements of erosion and deposition. Rotation of collector discs behind apertures allows recording of the long term evolution of deposition. QMBs measure mass change via the frequency deviations of vibrating quartz crystals. These diagnostics are used to investigate erosion/deposition during JET-C carbon operation and JET-ILW (ITER-like wall) beryllium/tungsten operation. A simple geometrical model utilising experimental data is used to model the time-dependent collector deposition profiles, demonstrating good qualitative agreement with experimental results. Overall, the JET-ILW collector deposition is reduced by an order of magnitude relative to JET-C, with beryllium replacing carbon as the dominant deposit. However, contrary to JET-C, in JET-ILW there is more deposition on the outer collector than the inner. This reversal of deposition asymmetry is investigated using an analysis of QMB data and is attributed to the different chemical properties of carbon and beryllium.
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| 15. |
- Bergsåker, Henric, et al.
(författare)
-
Assessment of the strength of kinetic effects of parallel electron transport in the SOL and divertor of JET high radiative H-mode plasmas using EDGE2D-EIRENE and KIPP codes
- 2018
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP PUBLISHING LTD. - 0741-3335 .- 1361-6587. ; 60:11
-
Tidskriftsartikel (refereegranskat)abstract
- The kinetic code for plasma periphery (KIPP) was used to assess the importance of the kinetic effects of parallel electron transport in the scrape-off layer (SOL) and divertor of JET high radiative H-mode inter-ELM plasma conditions with the ITER-like wall and strong nitrogen (N-2) injection. Plasma parameter profiles along a magnetic field from one of the EDGE2D-EIRENE simulation cases were used as an input for KIPP runs. Profiles were maintained by particle and power sources. KIPP generated electron distribution functions, f(e), parallel power fluxes, electron-ion thermoforces, Debye sheath potential drops and electron sheath transmission factors at divertor targets. For heat fluxes in the main SOL, KIPP results showed deviations from classical (e.g. Braginskii) fluxes by factors typically of similar to 1.5, sometimes up to 2, with the flux limiting for more upstream positions and flux enhancement near entrances to the divertor. In the divertor, at the same time, for radial positions closer to the separatrix, very large heat flux enhancement factors of up to ten or even higher, indicative of a strong nonlocal heat transport, were found at the outer target, with heat power flux density exhibiting bump-on-tail features at high energies. Under such extreme conditions, however, contributions of conductive power fluxes to total power fluxes were strongly reduced, with convective power fluxes becoming comparable, or sometimes exceeding, conductive power fluxes. Electron-ion thermoforce, on the other hand, which is known to be determined mostly by thermal and subthermal electrons, was found to be in good agreement with Braginskii formulas, including the Z(eff) dependence. Overall, KIPP results indicate, at least for the plasma conditions used in this modelling, a sizable, but not dominant, effect of kinetics on parallel electron transport.
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| 16. |
- Bernardo, J., et al.
(författare)
-
Ion temperature and toroidal rotation in JET's low torque plasmas
- 2016
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 87:11
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the procedure developed as the best method to provide an accurate and reliable estimation of the ion temperature T-i and the toroidal velocity v(phi) from Charge-eXchange Recombination Spectroscopy (CXRS) data from intrinsic rotation experiments at the Joint European Torus with the carbon wall. The low impurity content observed in such plasmas, resulting in low active CXRS signal, alongside low Doppler shifts makes the determination of Ti and v(phi) particularly difficult. The beam modulation method will be discussed along with the measures taken to increase photon statistics and minimise errors from the absolute calibration and magneto-hydro-dynamics effects that may impact the CXRS passive emission.
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| 17. |
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| 18. |
- Binda, Federico, 1987-, et al.
(författare)
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Analysis of the fast ion tails observed in the NE213pulse height specta measured during third harmonicradio-frequency heating experiments at JET
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we investigate the possibility of using a NE213 liquid scintillator as aneutron spectrometer to diagnose the fast ion tails produced in experiments with 3rd harmonicradio-frequency heating.We discuss mainly the instrumental effects that need to be considered and corrected for in orderto obtain a good agreement between measured data and models: gain drift, pile-up, impact of theassumption of a standard proton light yield function. We also address problems related to thepresence of triton burn-up events in the spectrum.The expected ion distribution is obtained from a simple 1D Fokker-Planck model. The parametersof the model are estimated using the data collected by the TOFOR neutron spectrometer.The agreement between the data and the model is good and it is possible to make a clear distinctionbetween discharges that had different electron densities and thus different cut-off energies. Wecan conclude that NE213 scintillators can provide useful spectroscopic information for this kind ofexperiments.
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| 19. |
- Binda, Federico, 1987-, et al.
(författare)
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Calculation of the profile-dependent neutron backscatter matrix for the JET neutron camera system
- 2017
-
Ingår i: Fusion engineering and design. - : ELSEVIER SCIENCE SA. - 0920-3796 .- 1873-7196. ; 123, s. 865-868
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the dependence of the backscatter component of the neutron spectrum on the emissivity profile. We did so for the JET neutron camera system, by calculating a profile-dependent backscatter matrix for each of the 19 camera channels using a MCNP model of the JET tokamak. We found that, when using a low minimum energy for the summation of the counts in the neutron pulse height spectrum, the backscatter contribution can depend significantly on the emissivity profile. The maximum variation in the backscatter level was 24% (8.0% when compared to the total emission). This effect needs to be considered when a correction for the backscatter contribution is applied to the measured profile. (C) 2017 The Authors. Published by Elsevier B.V.
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| 20. |
- Binda, Federico, 1987-
(författare)
-
Characterization of a NE-213 liquid scintillator for neutron flux measurement at JET
- 2011
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The measurment of the total neutron rate from a nuclear fusion reactor is very important in order to calculate the power produced in a plasma. An improvement of a method currently in use at JET will involve the installation of an organic liquid scintillator NE-213 of 1 cm3 of volume combined with a digital acquisition card. In this project a first stage of the characterization of the digitizer and of the detector has been performed.
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| 21. |
- Binda, Federico, et al.
(författare)
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Forward fitting of experimental data from a NE213 neutron detector installed with the magnetic proton recoil upgraded spectrometer at JET
- 2014
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 85:11, s. 11E123-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the results obtained from the data analysis of neutron spectra measured with a NE213 liquid scintillator at JET. We calculated the neutron response matrix of the instrument combining MCNPX simulations, a generic proton light output function measured with another detector and the fit of data from ohmic pulses. For the analysis, we selected a set of pulses with neutral beam injection heating (NBI) only and we applied a forward fitting procedure of modeled spectral components to extract the fraction of thermal neutron emission. The results showed the same trend of the ones obtained with the dedicated spectrometer TOFOR, even though the values from the NE213 analysis were systematically higher. This discrepancy is probably due to the different lines of sight of the two spectrometers (tangential for the NE213, vertical for TOFOR). The uncertainties on the thermal fraction estimates were from 4 to 7 times higher than the ones from the TOFOR analysis.
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| 22. |
- Binda, Federico, 1987-, et al.
(författare)
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Generation of the neutron response function of an NE213 scintillator for fusion applications
- 2017
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER. - 0168-9002 .- 1872-9576. ; 866, s. 222-229
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we present a method to evaluate the neutron response function of an NE213 liquid scintillator. This method is particularly useful when the proton light yield function of the detector has not been measured, since it is based on a proton light yield function taken from literature, MCNPX simulations, measurements of gammarays from a calibration source and measurements of neutrons from fusion experiments with ohmic plasmas. The inclusion of the latter improves the description of the proton light yield function in the energy range of interest (around 2.46 MeV). We apply this method to an NE213 detector installed at JET, inside the radiation shielding of the magnetic proton recoil (MPRu) spectrometer, and present the results from the calibration along with some examples of application of the response function to perform neutron emission spectroscopy (NES) of fusion plasmas. We also investigate how the choice of the proton light yield function affects the NES analysis, finding that the result does not change significantly. This points to the fact that the method for the evaluation of the neutron response function is robust and gives reliable results. (C) 2017 Published by Elsevier B.V.
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| 23. |
- Binda, Federico, 1987-
(författare)
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High Count Rate Neutron Detector Installation at JET
- 2011
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The measurement of fusion power is of paramount importance for the control of a fusion reactor's operation. The neutron yield from the reactor is strictly related to the energy production. One of the methods employed at JET to measure the yield involves the use of the MPRu spectrometer together with the neutron camera. However the MPRu has an intrinsically low efficiency (about 10-6), which results in a poor time resolution. An improvement involving the installation of a NE213 detectorfor high count rate has been proposed. The testing phase of the new instrumentation, conducted at Uppsala University, has shown that the acquisition system works properly and it is ready to be installed on site in view of the coming JET experimental campaign.
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| 24. |
- Binda, Federico, 1987-
(författare)
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Liquid scintillators as neutron diagnostic tools for fusion plasmas : System characterization and data analysis
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The neutrons produced in fusion devices carry information about various properties of the ions that are reacting in the machine. Measurements of the neutron flux and energy distribution can therefore be used to study the behaviour of the plasma ions under different experimental conditions.Several neutron detection techniques are available, each having advantages and disadvantages compared to the others. In this thesis we study neutron measurements performed with NE213 liquid scintillators. One advantage of NE213s compared to other neutron detection techniques is that they are simple to use, small and cheap. On the other hand, their response to neutrons makes the extraction of information about the neutron energy less precise.In the thesis we present the development of methods for the characterization and the data analysis of NE213 detectors. The work was performed using two instruments installed at the Joint European Torus (JET) tokamak in the UK: the “Afterburner” detector, which is an NE213 installed on a tangential line of sight, and the neutron camera, which is a system composed of 19 NE213 detectors installed on different lines of sight (10 horizontal and 9 vertical).The analysis of data from the Afterburner detector was focused on resolving different features of the neutron energy spectra which are related to different properties of the ion velocity distribution.The analysis of data from the neutron camera was directed towards the investigation of the spatial distribution of ions in the plasma. However, the individual characterization of the camera detectors allowed the inclusion of information about the energy distribution of the ions in the analysis.The outcomes of the studies performed indicate that the methods developed give reliable results and can therefore be applied to extract information about the plasma ions. In particular, the possibility of performing neutron emission spectroscopy analysis in each line of sight of a neutron camera is of great value for future studies.
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| 25. |
- Binda, Federico, et al.
(författare)
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Monte Carlo Simulation Of The Data Acquisition Chain Of Scintillation Detectors
- 2014
-
Ingår i: International Conference on Fusion Reactor Diagnostics, SEP 09-13, 2013, Varenna, ITALY. - : AIP Publishing LLC. - 9780735412484 ; , s. 101-104
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Konferensbidrag (refereegranskat)abstract
- The good performance of a detector can be strongly affected by the instrumentation used to acquire the data. The possibility of anticipating how the acquisition chain will affect the signal can help in finding the best solution among different set-ups. In this work we developed a Monte Carlo code that aims to simulate the effect of the various components of a digital Data Acquisition system (DAQ) applied to scintillation detectors. The components included in the model are: the scintillator, the photomultiplier tube (PMT), the signal cable and the digitizer. We benchmarked the code against real data acquired with a NE213 scintillator, comparing simulated and real signal pulses induced by gamma-ray interaction. Then we studied the dependence of the energy resolution of a pulse height spectrum (PHS) on the sampling frequency and the bit resolution of the digitizer. We found that exceeding some values of the sampling frequency and the bit resolution improves only marginally the performance of the system. The method can be applied for the study of various detector systems relevant for nuclear techniques, such as in fusion diagnostics.
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