Overview of ASDEX Upgrade results

The ASDEX Upgrade (AUG) programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of 3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF operation. As predicted, a factor two reduction on the ICRF-induced W plasma content could be achieved by the reduction of the sheath voltage at the antenna limiters via the compensation of the image currents of the central and side straps in the antenna frame. There are two main operational scenario lines in AUG. Experiments with low collisionality, which comprise current drive, ELM mitigation/suppression and fast ion physics, are mainly done with freshly boronized walls to reduce the tungsten influx at these high edge temperature conditions. Full ELM suppression and non-inductive operation up to a plasma current of Ip = 0.8 MA could be obtained at low plasma density. Plasma exhaust is studied under conditions of high neutral divertor pressure and separatrix electron density, where a fresh boronization is not required. Substantial progress could be achieved for the understanding of the confinement degradation by strong D puffing and the improvement with nitrogen or carbon seeding. Inward/outward shifts of the electron density profile relative to the temperature profile effect the edge stability via the pressure profile changes and lead to improved/decreased pedestal performance. Seeding and D gas puffing are found to effect the core fueling via changes in a region of high density on the high field side (HFSHD). The integration of all above mentioned operational scenarios will be feasible and naturally obtained in a large device where the edge is more opaque for neutrals and higher plasma temperatures provide a lower collisionality. The combination of exhaust control with pellet fueling has been successfully demonstrated. High divertor enrichment values of nitrogen En > 10 have been obtained during pellet injection, which is a prerequisite for the simultaneous achievement of good core plasma purity and high divertor radiation levels. Impurity accumulation observed in the all-metal AUG device caused by the strong neoclassical inward transport of tungsten in the pedestal is expected to be relieved by the higher neoclassical temperature screening in larger devices.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.Peer ReviewedPostprint (published version

Plasma physics code contribution to the Mont-Blanc project

This work develops strategies for adapting a particle-in-cell code to heterogeneous computer architectures and, in particular, to an ARM-based prototype of the Mont-Blanc project using OmpSs programming model and the OpenMP and OpenCL languages

Preparing plasma heating in ITER using integrated modelling

Nuclear fusion takes place when two light nuclei combine to make a heavier nucleus, releasing energy in the process. Magnetic confinement fusion attempts to achieve fusion and use this energy by confining the fuel in the form of a plasma. A plasma is a fully ionized gas whose behaviour is no longer dominated by short-ranged Coulomb forces, but by long-range electric and magnetic forces. Typically, plasmas are composed by hydrogen (H), helium (He), deuterium (D) or tritium (T) ions, or a combination of these. In this abstract, we tackle magnetic confinement fusion using tokamaks. Tokamaks are toroidal devices that have axial symmetry. They use poloidal and toroidal magnetic fields to create twisted magnetic field lines along which the charged particles travel in helical trajectories. In order for the plasma to reach the necessary temperatures for fusion to take place, auxiliary heating systems are used. In this abstract we focus on heating the plasma with electromagnetic waves in the ion cyclotron range of frequencies (ICRF). Significant advances have been made in the technological development of these magnetic confinement devices in order to progress towards the main goal of fusion research: to achieve electricity-producing fusion power stations that can provide energy reliably, safely and efficiently. The ratio of fusion power produced to the external power required to maintain the plasma in a steady state is known as the Q-factor. Fusion reactions provide energy to the plasma, which leads to self-heating and eventually to a self-sustained reaction, known as ignition. One of the long-term purposes of fusion research is to achieve this ignition (Q=infinite). However, no device so far has achieved a sustainable Q=1 plasma. The main candidate to do so is ITER (”The Way” in Latin), the largest tokamak nuclear fusion reactor, which is being built in the south of France and which is projected to start operating in 2025. The aim is for ITER to maintain Q≥5 and to reach Q=10 for a duration of 400-600s, demonstrating the feasibility of fusion power and of a ten-fold gain of plasma heating power. The commissioning of ITER is taking place through a staged approach. The First Plasma will be followed by an upgrade of the capabilities of the tokamak and two Pre-Fusion Power Operation (PFPO I and II) phases. In the PFPO phases, the basic controls and protection systems will be demonstrated, including the auxiliary heating and diagnostics systems, in experimental hydrogen (H) and helium (He) plasmas. The Fusion Power Operation (FPO) will start and a transition to deuterium (D) and deuterium-tritium (D-T) campaigns will be made. Most of the ICRF modelling that has been carried out so far for ITER has focused on heating scenarios relevant for the D, T and D-T plasmas in the FPO stage. There is a need to improve our understanding on the performance of ICRF in H and He plasmas in the PFPO phase of ITER, and on the heating schemes planned for this phase. In this abstract we use the ICRF heating code PION [1] integrated into the transport modelling workflow European Transport Solver (ETS) [2] to study and predict how the plasma will be heated when ICRF heating is applied to ITER PFPO plasmas. The integration into a transport modelling workflow is relevant because PION calculates the ICRF power deposition but it does not predict on its own how the heating will affect the plasma and how its parameters will evolve. A transport modelling workflow such as ETS, which has been developed inside the ITER Integrated Modelling & Analysis Suite (IMAS) [3], can calculate the evolution of the plasma discharge and provide the capabilities for self-consistent predictive simulations

Numerical simulations for the atomic beam probe

Fusion plasmas are complex systems with several physical parameters which need continuous control and adjustment. Most plasma diagnostics have limitations of applications regarding the spatial, temporal resolution with typically high relative error. A typical physical parameter is combined from the output of several diagnostics to reduce these limitations. The Atomic Beam Probe (ABP) is a novel diagnostic technique, and in our recent work, we are working on supportive numerical modelling procedures. Our tool has already been supporting diagnostic and scenario design, and we would like to give a hint about possible publication opportunitie

Analysis of the potential of ICRF waves to heat bulk ions in DEMO

While ITER’s main purpose is to confirm the feasibility of nuclear fusion as an energy source, DEMO is planned as the first fusion reactor to produce net electrical energy. Our analysis is carried out for the DEMO 2015 (from now on DEMO2), using the ICRF modelling codes PION and TORIC. We also have analyzed the previous design DEMO 2013 (from now on DEMO1)This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. We are grateful to Dr. R. Wenninger and Dipl.-Ing T. Franke (PPPT, Garching) for DEMO parameters.Peer ReviewedPostprint (published version

Lifetime effects and satellites in the photoelectron spectrum of tungsten metal

Tungsten (W) is an important and versatile transition metal and has a firm place at the heart of many technologies. A popular experimental technique for the characterization of tungsten and tungsten-based compounds is x-ray photoelectron spectroscopy (XPS), which enables the assessment of chemical states and electronic structure through the collection of core level and valence band spectra. However, in the case of tungsten metal, open questions remain regarding the origin, nature, and position of satellite features that are prominent in the photoelectron spectrum. These satellites are a fingerprint of the electronic structure of the material and have not been thoroughly investigated, at times leading to their misinterpretation. The present work combines high-resolution soft and hard x-ray photoelectron spectroscopy (SXPS and HAXPES) with reflected electron energy loss spectroscopy (REELS) and a multitiered ab initio theoretical approach, including density functional theory (DFT) and many-body perturbation theory (G0W0 and GW + C ), to disentangle the complex set of experimentally observed satellite features attributed to the generation of plasmons and interband transitions. This combined experiment-theory strategy is able to uncover previously undocumented satellite features, improving our understanding of their direct relationship to tungsten's electronic structure. Furthermore, it lays the groundwork for future studies into tungsten-based mixed-metal systems and holds promise for the reassessment of the photoelectron spectra of other transition and post-transition metals, where similar questions regarding satellite features remain.CK acknowledges the support from the Department of Chemistry, UCL. NKF acknowledges support from the Engineering and Physical Sciences Research Council (EP/L015277/1). AR acknowledges the support fromthe Analytical Chemistry Trust Fund for her CAMS-UK Fellowship. LER acknowledges support from an EPSRC Early Career Research Fellowship (EP/P033253/1). JL and JMK acknowledge funding from EPSRC under Grant No. EP/R002010/1 and from a Royal Society University Research Fellowship (URF/R/191004). This work used the ARCHER UK National Supercomputing Service via JL’s membership of the HEC Materials Chemistry Consortium of UK, which is funded by EPSRC (EP/L000202). JJGM and SM acknowledge the support from the FusionCAT project (001-P-001722) cofinanced by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible, the access to computational resources at MareNostrum and the technical support provided by BSC (RES-QS-2020-3-0026). Part of this work was carried out using supercomputer resources provided under the EU-JA Broader Approach collaboration in the Computational Simulation Centre of International Fusion Energy Research Centre (IFERC-CSC)Peer Reviewed"Article signat per 13 autors/es: C. Kalha, L. E. Ratcliff, J. J. Gutiérrez Moreno, S. Mohr, M. Mantsinen, N. K. Fernando, P. K. Thakur, T.-L. Lee, H.-H. Tseng, T. S. Nunney, J. M. Kahk, J. Lischner, and A. Regoutz"Postprint (author's final draft

Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall

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 Alfvèn 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.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No. 633053Postprint (published version

The power threshold of H-mode access in mixed hydrogen–tritium and pure tritium plasmas at JET with ITER-like wall

The heating power to access the high confinement mode (H-mode), PLH, scales approximately inversely with the isotope mass of the main ion plasma species as found in (protonic) hydrogen, deuterium and tritium plasmas in many fusion facilities over the last decades. In first dedicated L–H transition experiments at the Joint European Torus (JET) tokamak facility with the ITER-like wall (ILW), the power threshold, PLH, was studied systematically in plasmas of pure tritium and hydrogen–tritium mixtures at a magnetic field of 1.8 T and a plasma current of 1.7 MA in order to assess whether this scaling still holds in a metallic wall device. The measured power thresholds, PLH, in Ohmically heated tritium plasmas agree well with the expected isotope scaling for metallic walls and the lowest power threshold was found in Ohmic phases at low density. The measured power thresholds in ion cyclotron heated plasmas of pure tritium or hydrogen–tritium mixtures are significantly higher than the expected isotope mass scaling due to higher radiation levels. However, when the radiated power is taken into account, the ion cyclotron heated plasmas exhibit similar power thresholds as a neutral beam heated plasma, and are close to the scaling. The tritium plasmas in this study tended to higher electron heating fractions and, when heated with ion cyclotron waves, to relatively higher radiation fractions compared to other isotopes potentially impeding access to sustained H-modes.The authors thank P.A. Schneider, F. Ryter, A. Nielsen, and A. Kappatou for fruitful discussions and for help with data analysis tools. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. G. Birkenmeier received funding from the Helmholtz Association under Grant No. VH-NG-1350.Peer Reviewed"Article signat per 27 autors/es: G. Birkenmeier, E.R. Solano, E. Lerche, D. Taylor, D. Gallart, M.J. Mantsinen, E. Delabie, I.S. Carvalho, P. Carvalho, E. Pawelec, J.C. Hillesheim, F. Parra Diaz, C. Silva, S. Aleiferis, J. Bernardo, A. Boboc, D. Douai, E. Litherland-Smith, R. Henriques, K.K. Kirov, C.F. Maggi, J. Mailloux, M. Maslov, F.G. Rimini, S.A. Silburn, P. Sirén, H. Weisen and JET Contributors"Postprint (published version

Effect of inclusion of pitch-angle dependence on a simplified model of RF deposition in tokamak plasma

Using the PION ICRH modelling code and comparisons against JET tokamak experiments, the effect of including pitch angle dependence within the RF diffusion operator on the fast ion particle distribution functions is quantified. It is found to be of greatest importance in cases of higher harmonic heating and lower heating ion mass, resulting in faster drop-off of the distribution's high energy tail. We see differences of several orders of magnitude in the high-energy range and significant non-linear alterations by several tens of percent to ion species power partition. ITER scenario operational parameters are also considered, and this improved treatment is shown to benefit anticipated ITER scenarios with second harmonic hydrogen heating, according to our predictions. PION's combination of benchmarked simplified wave physics and Fokker-Planck treatment offers modelling advantages. Since including the pitch angle dependence in the RF diffusion operator has not led to a significant increase in the required computing time when modelling different ICRF schemes in JET discharges, it has been made available within the production code.The CCFE part of this work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The BSC part of this project is co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014–2020 with a grant of 50% of total cost eligible. The authors are grateful to Jacob Eriksson for assistance with experimental data, to Lars-Göran Eriksson for discussions on the implementation of the new features, and to Colin Roach and Michael Fitzgerald for valuable comments on the manuscript.Peer ReviewedPostprint (published version