A new edge beam emission polarimetry diagnostic dedicated to the measurement of the magnetic field line angle has been installed on the ASDEX Upgrade tokamak. The new diagnostic relies on the motional Stark e ff ect and is based on the simultaneous measurement of the polarization direction of the linearly polarized π (parallel to the electric field) and σ (perpendicular to the electric field) lines of the Balmer line D α . The technical properties of the system are described. The calibration procedures are discussed and first measurements are presented ; European Union (EUROfusion 633053) ; European Union (EUROfusion Grant WP14-FRF-IPP) ; Ministerio de Economía y Competitividad (Grant No. FJCI-201422139)
Nuclear fusion is expected to be a clean and almost-unlimited power source in the near future. The first net power demonstration plant (DEMO) is planned to start operation in 2050. The supercritical carbon dioxide (S-CO) Brayton cycle is an excellent candidate for integration with a fusion power plant, such as DEMO, because of its high efficiency at intermediate temperatures and low interaction of coolant with tritium. This work analyses a set of S-CO Brayton cycle layouts for its integration in a DEMO-like fusion power plant, considering the specific requirements and heat availability characteristics. A framework has been developed to integrate the PROCESS code and the numerical solver EES to study the thermal and economic aspects of integrating the different S-CO cycle layouts. In total, 14 layouts have been studied and grouped into a more conservative (DEMO1, pulsed operation) and more advanced (DEMO2, steady-state operation) fusion reactors. The PROCESS code has been used to obtain the DEMO 2018 Baseline, which defines the available power from each heat source and their boundary conditions. This code has also been used to assess the cost of the optimal layout. Thermal storage has been added to the DEMO1 scenario to avoid standby times that could negatively affect the cycle equipment lifetime and efficiency. Besides, these boundary conditions have been extended to account for possible technical improvements by the time of its construction in the DEMO2 scenario. A sensitivity analysis of the most characteristic parameters of the cycles shows a strong dependence on the turbine inlet temperature for all layouts, which is constrained by the reactor material limits. The cycle efficiency (electric power produced before consumptions non-related to the cycle) has been selected as the figure of merit for the optimisation. The results show a 38% cycle efficiency for DEMO1 and 56% for DEMO2 scenarios. These efficiencies drop to 20% and 38% values, respectively, when the reactor and cooling loop power consumptions are considered. These values are obtained for current fusion reactor conceptual designs. The economic analysis shows the economic viability of DEMO2 scenarios. ; The authors would like to thank J. Morris, M. Kovari and the rest of the PROCESS team of UKAEA for discussion and guidance on using the UKAEA systems code PROCESS for this work. The authors gratefully acknowledge the financial support of the Spanish Ministry of Science, Innovation and Universities (grant FPU17/06273), the H2020 Marie-Sklodowska Curie programme (grant agreement No. 708257) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 805162).
The confinement of neutral beam injection (NBI) particles in the presence of n = 3 resonant magnetic perturbations (RMPs) in 15 MA ITER DT plasmas has been studied using full orbit ASCOT simulations. Realistic NBI distribution functions, and 3D wall and equilibria, including the plasma response to the externally applied 3D fields calculated with MARS-F, have been employed. The observed total fast-ion losses depend on the poloidal spectra of the applied n = 3 RMP as well as on the absolute toroidal phase of the applied perturbation with respect to the NBI birth distribution. The absolute toroidal phase of the RMP perturbation does not affect the ELM control capabilities, which makes it a key parameter in the confinement optimization. The physics mechanisms underlying the observed fast-ion losses induced by the applied 3D fields have been studied in terms of the variation of the particle canonical angular momentum (δPϕ) induced by the applied 3D fields. The presented simulations indicate that the transport is located in an edge resonant transport layer as observed previously in ASDEX upgrade studies. Similarly, our results indicate that an overlapping of several linear and nonlinear resonances at the edge of the plasma might be responsible for the observed fast-ion losses. The results presented here may help to optimize the RMP configuration with respect to the NBI confinement in future ITER discharges. ; Spanish Ministry of Science, Innovation and Universities (grant BES2013-065501) ; EUROfusion Consortium grant agreement No. 633053 ; European Union's Horizon 2020 (grant agreement No. 805162) ; Academy of Finland project No. 324759
The dynamic behaviour of the ion and electron energy, particle and momentum transport measured during type-I edge localized mode (ELM) cycles at ASDEX Upgrade is presented. Fast measurements of the ion and electron temperature profiles revelead that the ion and electron energy transport recover on different timescales, with the electrons recovering on a slower timescale (Cavedon et al 2017 Plasma Phys. Control. Fusion 59 105007). The dominant mechanism for the additional energy transport in the electron channel that could cause the delay in the electron temperature gradient (VTe) recovery is attributed to the depletion of energy caused by the ELM. The local sources and sinks for the electron channel in the steep gradient region are much smaller compared to the energy flux arriving from the pedestal top, indicating that the core plasma may dictate the local dynamics of the VTe recovery during the ELM cycle. A model for the edge momentum transport based on toroidal torque balance that takes into account the existence of poloidal impurity asymmetries has been developed. The analysis of the profile evolution during the ELM cycle shows that the model captures the dynamics of the rotation both before the ELM crash and during the recovery phase. ; European Commission (Euratom) Grant agreement No. 633053 ; H2020 Marie-Sklodowska Curie programme (grant agreement No. 708257) ; European Union's Horizon 2020 (grant agreement No. 805162)
Properties of the Imode confinement regime on the ASDEX Upgrade tokamak are summarized. A weak dependence of the power threshold for the LI transition on the toroidal magnetic field strength is found. During improved confinement, the edge radial electric field well deepens. Stability calculations show that the Imode pedestal is peelingballooning stable. Turbulence investigations reveal strongly intermittent density fluctuations linked to the weakly coherent mode in the confined plasma, which become stronger as the confinement quality increases. Across all investigated structure sizes ( ≈ ⊥ k 5 – 12 cm − 1 , with ⊥ k the perpendicular wavenumber of turbulent density fluctuations), the intermittent turbulence bursts are observed. Comparison with bolometry data shows that they move poloidally toward the Xpoint and finally end up in the divertor. This might be indicative that they play a role in inhibiting the density profile growth, such that no pedestal is formed in the edge density profile. ; European Union (EUROfusion 633053) ; European Union (EUROfusion AWP15ENR09/IPP02)
The ion heat transport in the pedestal of H-mode plasmas is investigated in various H-mode discharges with different pedestal ion collisionalities. Interpretive modelling suggests that in all analyzed discharges the ion heat diffusivity coefficient, χ i , in the pedestal is close to the neoclassical prediction within the experimental uncertainties. The impact of changing the deposition location of the electron cyclotron resonance heating on the ion heat transport has been studied. The effect on the background profiles is small. The pre-ELM (edge localized modes) edge profiles as well as the behaviour of the electron temperature and density, ion temperature and impurity toroidal rotation during the ELM cycle are very similar in discharges with on- and off-axis ECRH heating. No significant deviation of χ i from neoclassics is observed when changing the ECRH deposition location to the plasma edge. ; European Commission (EUROfusion 633053) ; European Union (EUROfusion Grant WP14-FRF-IPP)
Computer simulations are invaluable tools for scientific discovery. However, accurate simulations are often slow to execute, which limits their applicability to extensive parameter exploration, large-scale data analysis, and uncertainty quantification. A promising route to accelerate simulations by building fast emulators with machine learning requires large training datasets, which can be prohibitively expensive to obtain with slow simulations. Here we present a method based on neural architecture search to build accurate emulators even with a limited number of training data. The method successfully emulates simulations in 10 scientific cases including astrophysics, climate science, biogeochemistry, high energy density physics, fusion energy, and seismology, using the same super-architecture, algorithm, and hyperparameters. Our approach also inherently provides emulator uncertainty estimation, adding further confidence in their use. We anticipate this work will accelerate research involving expensive simulations, allow more extensive parameters exploration, and enable new, previously unfeasible computational discovery. ; UK EPSRC Grant EP/P015794/1 and the Royal Society ; UK EPSRC (EP/M022331/1 and EP/N014472/1) ; European Union's Horizon 2020 (Grant Agreement No. 805162) ; Natural Environment Research Council (NERC) NE/P013406/1 (A-CURE)
An Imaging Neutral Particle Analyzer (INPA) diagnostic has been designed for the ASDEX Upgrade (AUG) tokamak. The AUG INPA diagnostic will measure fast neutrals escaping the plasma after charge exchange reactions. The neutrals will be ionized by a 20 nm carbon foil and deflected toward a scintillator by the local magnetic field. The use of a neutral beam injector (NBI) as an active source of neutrals will provide radially resolved measurements, while the use of a scintillator as an active component will allow us to cover the whole plasma along the NBI line with unprecedented phase-space resolution (<12 keV and 8 cm) and a fast temporal response (up to 1 kHz with the high resolution acquisition system and above 100 kHz with the low resolution one), making it suitable to study localized fast-ion redistributions in phase space. ; European Union's Horizon 2020 (Grant Agreement No. 805162) ; Ministerio de Ciencia, Innovación y Universidades (Grant No. FPU19/02486)
An imaging heavy ion beam probe (i-HIBP) diagnostic, for the simultaneous measurement of plasma density, magnetic field and electrostatic potential in the plasma edge, has been installed at ASDEX Upgrade. Unlike standard heavy ion beam probes, in the i-HIBP the probing (heavy) ions are collected by a scintillator detector, creating a light pattern or strike-line, which is then imaged by a camera. Therefore, a good characterization of the scintillator response is needed. Previous works focused on the scintillator behaviour against irradiation with light ions such as hydrogen and alpha particles. In this work we present the characterization of several scintillator screens — TG-Green (SrGa2S4:Eu2+), YAG-Ce (Y3Al5O12:Ce3+) and P11 (ZnS:Ag) — against irradiation with 133Cs+ ions, in an energy range between 5 and 70 keV and ion currents between 105 and 107ions/(s·cm2). Three main properties of the scintillators have been studied: the ionolumenescence efficiency or yield, the linearity and the degradation as a function of the fluence. The highest yield was delivered by the TG-Green scintillator screen with > 8·103 photons/ion at 50 keV. All the samples showed a linear response with increasing incident ion flux. The degradation was quantified in terms of the fluence F1/2, which leads to a reduction of the emissivity by a factor of 2. TG-Green showed the lowest degradation with F1/2= 5.4·1014ions/cm2. After the irradiation the samples were analyzed by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE). No trace of Cs was found in the irradiated regions. These results indicate that, among the tested materials, TG-Green is the best candidate for the i-HIBP detector. ; European Union's Horizon 2020 (grant agreement No. 805162) ; Helmholtz Association VHNG-1350 ; Spanish Ministry of Science and Innovation FJC2019-041092-I.
An Imaging Neutral Particle Analyzer (INPA) diagnostic has been designed for the ASDEX Upgrade (AUG) tokamak. The AUG INPA diagnostic will measure fast neutrals escaping the plasma after charge exchange reactions. The neutrals will be ionized by a 20 nm carbon foil and deflected toward a scintillator by the local magnetic field. The use of a neutral beam injector (NBI) as an active source of neutrals will provide radially resolved measurements, while the use of a scintillator as an active component will allow us to cover the whole plasma along the NBI line with unprecedented phase-space resolution (<12 keV and 8 cm) and a fast temporal response (up to 1 kHz with the high resolution acquisition system and above 100 kHz with the low resolution one), making it suitable to study localized fast-ion redistributions in phase space. ; This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 805162) and the Spanish Ministerio de Ciencia, Innovación y Universidades (Grant No. FPU19/02486).
The SMall Aspect Ratio Tokamak (SMART) device is a new compact (plasma major radius R≥0.40 m, minor radius a≥0.20 m, aspect ratio A≥1.7) spherical tokamak, currently in development at the University of Seville. The SMART device has been designed to achieve a magnetic field at the plasma center of up to B=1.0 T with plasma currents up to I=500 kA and a pulse length up to τ=500 ms. A wide range of plasma shaping configurations are envisaged, including triangularities between −0.50≤δ≤0.50 and elongations of κ≤2.25. Control of plasma shaping is achieved through four axially variable poloidal field coils (PF), and four fixed divertor (Div) coils, nominally allowing operation in lower-single null, upper-single null and double-null configurations. This work examines phase 2 of the SMART device, presenting a baseline reference equilibrium and two highly-shaped triangular equilibria. The relevant PF and Div coil current waveforms are also presented. Equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents. ; The authors would like to thank the VEST team for their technical and engineering support. This work received funding from the Fondo Europeo de Desarollo Regional (FEDER) by the European Commission under grant agreement numbers IE17-5670 and US-15570. In addition support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 805162) is gratefully acknowledged.
