| 1. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 2. |
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| 3. |
- Bonanomi, N., et al.
(författare)
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Role of fast ion pressure in the isotope effect in JET L-mode plasmas
- 2019
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 59:9
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of JET ITER-like wall L-mode experiments in hydrogen and deuterium (D) plasmas, dedicated to the study of the isotope dependence of ion heat transport by determination of the ion critical gradient and stiffness by varying the ion cyclotron resonance heating power deposition. When no strong role of fast ions in the plasma core is expected, the main difference between the two isotope plasmas is determined by the plasma edge and the core behavior is consistent with a gyro-Bohm scaling. When the heating power (and the fast ion pressure) is increased, in addition to the difference in the edge region, also the plasma core shows substantial changes. The stabilization of ion heat transport by fast ions, clearly visible in D plasmas, appears to be weaker in H plasmas, resulting in a higher ion heat flux in H with apparent anti-gyro-Bohm mass scaling. The difference is found to be caused by the different fast ion pressure between H and D plasmas, related to the heating power settings and to the different fast ion slowing down time, and is completely accounted for in non-linear gyrokinetic simulations. The application of the TGLF quasi-linear model to this set of data is also discussed.
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| 4. |
- Cannas, Barbara, et al.
(författare)
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Recurrence Plots for Dynamic Analysis of Type-I ELMs at JET With a Carbon Wall
- 2019
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 47:4, s. 1871-1877
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the dynamic characteristics of type-I edge-localized modes (ELM) time series from the JET tokamak, the world's largest magnetic confinement plasma physics experiment, have been investigated through recurrence plots (RPs). The analysis has been focused on RPs of pedestal temperature, line averaged electron density, and outer divertor D-alpha time series during experiments with a carbon wall. The analysis of RPS shows the patterns similar to those characteristics of signals exhibiting type-2 intermittency, in particular, a characteristic kite-like shape; this gives useful hints to model the temperature signal as well as the D-alpha radiation time series, with simple nonlinear maps capturing the nearly periodic behavior of type-I ELMs.
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| 5. |
- Carvalho, D. D., et al.
(författare)
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Deep neural networks for plasma tomography with applications to JET and COMPASS
- 2019
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Convolutional neural networks (CNNs) have found applications in many image processing tasks, such as feature extraction, image classification, and object recognition. It has also been shown that the inverse of CNNs, so-called deconvolutional neural networks, can be used for inverse problems such as plasma tomography. In essence, plasma tomography consists in reconstructing the 2D plasma profile on a poloidal cross-section of a fusion device, based on line-integrated measurements from multiple radiation detectors. Since the reconstruction process is computationally intensive, a deconvolutional neural network trained to produce the same results will yield a significant computational speedup, at the expense of a small error which can be assessed using different metrics. In this work, we discuss the design principles behind such networks, including the use of multiple layers, how they can be stacked, and how their dimensions can be tuned according to the number of detectors and the desired tomographic resolution for a given fusion device. We describe the application of such networks at JET and COMPASS, where at JET we use the bolometer system, and at COMPASS we use the soft X-ray diagnostic based on photodiode arrays.
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| 6. |
- Eriksson, Frida, 1986, et al.
(författare)
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Interpretative and predictive modelling of Joint European Torus collisionality scans
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : Institute of Physics Publishing (IOPP). - 0741-3335 .- 1361-6587. ; 61:11
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Tidskriftsartikel (refereegranskat)abstract
- Transport modelling of Joint European Torus (JET) dimensionless collisionality scaling experiments in various operational scenarios is presented. Interpretative simulations at a fixed radial position are combined with predictive JETTO simulations of temperatures and densities, using the TGLF transport model. The model includes electromagnetic effects and collisions as well as (E)over-right-arrow x (b)over-right-arrow shear in Miller geometry. Focus is on particle transport and the role of the neutral beam injection (NBI) particle source for the density peaking. The experimental 3-point collisionality scans include L-mode, and H-mode (D and H and higher beta D plasma) plasmas in a total of 12 discharges. Experimental results presented in (Tala et al 2017 44th EPS Conf.) indicate that for the H-mode scans, the NBI particle source plays an important role for the density peaking, whereas for the L-mode scan, the influence of the particle source is small. In general, both the interpretative and predictive transport simulations support the experimental conclusions on the role of the NBI particle source for the 12 JET discharges.
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| 7. |
- Garcia, J., et al.
(författare)
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First principles and integrated modelling achievements towards trustful fusion power predictions for JET and ITER
- 2019
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 59:8
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Tidskriftsartikel (refereegranskat)abstract
- Predictability of burning plasmas is a key issue for designing and building credible future fusion devices. In this context, an important effort of physics understanding and guidance is being carried out in parallel to JET experimental campaigns in H and D by performing analyses and modelling towards an improvement of the understanding of DT physics for the optimization of the JET-DT neutron yield and fusion born alpha particle physics. Extrapolations to JET-DT from recent experiments using the maximum power available have been performed including some of the most sophisticated codes and a broad selection of models. There is a general agreement that 11-15 MW of fusion power can be expected in DT for the hybrid and baseline scenarios. On the other hand, in high beta, torque and fast ion fraction conditions, isotope effects could be favourable leading to higher fusion yield. It is shown that alpha particles related physics, such as TAE destabilization or fusion power electron heating, could be studied in ITER relevant JET-DT plasmas.
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| 8. |
- Kaur, Rajdeep, 1997-
(författare)
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Case Studies in Ion Beam Assisted Nanostructure Engineering
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Beams of energetic ions can be used for material analysis and modification. It provides us with a tool featuring unique control over the area, depth and amount of damage in the material. This property of ion beams can be used to generate desired changes in material properties or form nanostructures with specific characteristics in the material. While the modification of materials through the irradiation of GeV energy ions has been extensively researched, it is worth considering MeV ion irradiation for ion beam-based material modification. Accelerators with the ability to deliver ions in the MeV energy regime, such as tandem accelerators with a few MV terminal voltage and cyclotrons, are more accessible, easier to maintain and already available in industrial spaces. Thus, a comprehensive study on whether the damage caused in different material systems by MeV ion irradiation can be used for nanostructure engineering needs to be performed. In this thesis, the formation of nanostructures by MeV ion irradiation in two different materials is studied. The dependence of the nanostructures formed on the ion parameters such as ion type and energy is investigated for two material systems. In the first study, we investigate the formation of nanostructures on the surface of a model system, i.e., single crystals of CaF2. In the second study, we investigate the formation of etchable ion tracks in polyimide membranes. Nanoscale pores and channels, that can be formed from these etchable ion tracks, are expected to be the basis of next-generation detectors, biosensors and DNA/RNA sequencing. In the case of both materials, three distinct regions of ion-induced damage are identified after irradiation. The thresholds dividing these distinct regions of damage are dependent on ion velocity. Thus, electronic stopping power thresholds for the formation of nanostructures in materials are observed to be lower for MeV ions than for GeV ions.
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| 9. |
- Kaur, Rajdeep, et al.
(författare)
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Charge equilibration and irradiation damage threshold for MeV ions in polyimide
- 2024
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 551
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Tidskriftsartikel (refereegranskat)abstract
- Polyimide foils were irradiated with MeV ions below charge state equilibrium and etched in sodium hypochlorite solution to measure the material depth below which ion tracks occurred. It was observed that no etchable ion tracks were formed in the first few nanometres of the foil as the electronic stopping power was below the damage threshold. The damage threshold was crossed at a certain depth in the foil and intermittent tracks began to form. The measurement of depth for crossing the damage threshold in polyimide enabled verification of the previously theoretical models for the evolution of nonequilibrium charge variation of electronic stopping power during charge state equilibration of energetic ions and explicitly demonstrated that the equilibration process plays a role in ion-induced nanostructure formation.
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| 10. |
- Kaur, Rajdeep, et al.
(författare)
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Ion Track Formation and Nanopore Etching in Polyimide : Possibilities in the MeV Ion Energy Regime
- 2023
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Ingår i: Macromolecular materials and engineering. - : Wiley-VCH Verlagsgesellschaft. - 1438-7492 .- 1439-2054.
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Tidskriftsartikel (refereegranskat)abstract
- Polyimide films of thickness 7.5 µm are irradiated by a wide range of ions (1H to 197Au) with energies between 1.05 and 48 MeV. Irradiated samples are then chemically etched in sodium hypochlorite solution to investigate nanopore formation due to ion track etching. A threshold in terms of electronic stopping power, Set, needs to be surpassed to preferentially etch the ion tracks. Close to Set, intermittent tracks are formed where only part of the track is etchable. The fraction of these etchable parts increases as we move away from Set, toward higher stopping powers, eventually yielding continuous etchable tracks. Both intermittent and continuous track formation thresholds are observed to be velocity-dependent, yielding a decrease of the thresholds in the present work compared to previously reported thresholds for swift heavy ions. This finding leads the authors to suggest that electrostatic ion accelerators with terminal voltages of several MV are applicable for the production of ion track membranes up to ≈10–20 µm in thickness. Suitable ions for nanopores in 7.5 µm polyimide films include 42 MeV 59Co and 48 MeV 197Au. The growth mechanism for the pores during etching is discussed, relating it to the properties of the original ion track.
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