Periodic Reporting for period 3 - EUROfusion (Implementation of activities described in the Roadmap to Fusion during Horizon Europe through a joint programme of the members of the EUROfusion consortium)
Berichtszeitraum: 2023-01-01 bis 2023-12-31
In a pan-European collaboration under the umbrella of the EUROfusion consortium, almost 200 research institutes, universities, and R&D organisations work together towards the realisation of fusion energy. The optimal fusion process for power generation on earth is the fusion of the hydrogenic isotopes Deuterium and Tritium. The process requires a delicate balance between the magnetic confinement necessary to isolate the plasma inside the reactor volume away from the wall components, and the power created by the fusion process itself while dealing with the extremely hot plasma. Fusion is not a single technology but depends on a complex set of intertwined technologies from multiple disciplines. The main objective of the DEMOnstration fusion power plant (DEMO) design and technology R&D during Horizon Europe is to further advance the technical basis of a DEMO fusion power plant aiming at a complete integrated concept design. This includes detailed assessments of the technical feasibility, safety, licensing issues and life-cycle costs.
The last JET tokamak experimental campaigns provided valuable data regarding long stable plasma operation with minimal plasma facing component deterioration. The Deuterium-Tritium experiments at JET allowed to advance the capabilities of real time control methods to keep the balance of the fuel mix, recycling, and accounting of the Tritium fuel, and the development of techniques to stabilise Magneto-Hydrodynamic turbulence that generates bursts of plasma particles and energy to the walls.
Operations started on the JT-60SA tokamak (Japan) which is the model of a successful collaboration between Europe and Japan. The machine will be exploited jointly and will address the access to long pulse operation, few 100s of seconds, using super conducting magnetic coils to confine the plasma.
The W7-X Stellarator made progress in prolonging the high-performance phase and discharge duration in conditions relevant for reducing the heat loads to the plasma facing walls. The optimal heating mix to increase the temperature of the fuel ions in the core of the device was explored, and this topic will be further studied after the installation of the planned upgrades of the heating systems.
Experiments in several European facilities, either in linear machines (Pilot Surface Interaction (PSI-2) & MAGNUM-PSI in Netherlands) or tokamaks (WEST in France & ASDEX-Upgrade in Germany) were carried out to predict the lifetime of the tungsten tiles in the ITER divertor. A prompt redeposition factor of eroded Tungsten of up to 94% was confirmed experimentally in line with the results inferred from the JET tokamak experiments, yielding vital information regarding the Tungsten source strength in ITER. Plasma Wall Interaction and Exhaust processes in a reactor-like device such as erosion, migration, and deposition of Plasma-Facing Materials, and Tritium retention which are critical for the Plasma Facing Components lifetime, nuclear safety, and machine availability were also investigated. In particular, ion bombardment experiments mimicking the effect of neutrons in Tungsten materials were conducted up to 5 displacements per atom, showing a more than one order of magnitude increase in Tritium trapping sites, i.e. Tritium retention with plasma operation and associated neutron damage.
The development of a Pulse Design Tool has started in close collaboration with ITER. There were significant advancements in gyrokinetic and time-dependent simulations, as well as improvements in modelling tools and code interfaces.
Activities relating to the concept design of the EU-DEMO have progressed. The work packages responsible for the system design and technology R&D have continued the maturation and down-selection of variants. Design space exploration was a major focus in 2023. Several studies were conducted by the DEMO Central Team to define the optimum EU-DEMO design space, which is heavily constrained by physics and technology, aiming to minimise either the machine size or the technical risks. This included the assessment of the impact of varying certain stakeholder requirements, such as electricity output and pulse duration; the impact and associated risks of using high-field toroidal magnets, benefiting from promising high temperature superconductors; and machine configurations at low aspect ratio. The feasibility study of a volumetric neutron source has started aiming at completion by October 2024.
Lower aspect ratio configuration studies revealed that the plasma volume is not significantly affected when reducing the aspect ratio, however, the reattachment heat flux and magnetic field were reduced, leading to a new low aspect ratio baseline variant shown in Fig. 1. It was shown that reducing the electricity output from 500 MW to 100 MW, the device major radius drops by only 10% from 8.8 m to 8.0 m. On the other hand, increasing the duration of the pulse, keeping constant the net electricity power and accumulated neutron fluence, the major radius increases because the size of the central solenoid increases due to the required larger flux swings. It should also be noted that at very low pulse lengths i.e. below 1.5 hours, the size increases because of fatigue considerations, requiring thicker structures for the central solenoid.
Operations started on the JT-60SA tokamak (Japan) which is the model of a successful collaboration between Europe and Japan. The machine will be exploited jointly and will address the access to long pulse operation, few 100s of seconds, using super conducting magnetic coils to confine the plasma.
The W7-X Stellarator made progress in prolonging the high-performance phase and discharge duration in conditions relevant for reducing the heat loads to the plasma facing walls. The optimal heating mix to increase the temperature of the fuel ions in the core of the device was explored, and this topic will be further studied after the installation of the planned upgrades of the heating systems.
Experiments in several European facilities, either in linear machines (Pilot Surface Interaction (PSI-2) & MAGNUM-PSI in Netherlands) or tokamaks (WEST in France & ASDEX-Upgrade in Germany) were carried out to predict the lifetime of the tungsten tiles in the ITER divertor. A prompt redeposition factor of eroded Tungsten of up to 94% was confirmed experimentally in line with the results inferred from the JET tokamak experiments, yielding vital information regarding the Tungsten source strength in ITER. Plasma Wall Interaction and Exhaust processes in a reactor-like device such as erosion, migration, and deposition of Plasma-Facing Materials, and Tritium retention which are critical for the Plasma Facing Components lifetime, nuclear safety, and machine availability were also investigated. In particular, ion bombardment experiments mimicking the effect of neutrons in Tungsten materials were conducted up to 5 displacements per atom, showing a more than one order of magnitude increase in Tritium trapping sites, i.e. Tritium retention with plasma operation and associated neutron damage.
The development of a Pulse Design Tool has started in close collaboration with ITER. There were significant advancements in gyrokinetic and time-dependent simulations, as well as improvements in modelling tools and code interfaces.
Activities relating to the concept design of the EU-DEMO have progressed. The work packages responsible for the system design and technology R&D have continued the maturation and down-selection of variants. Design space exploration was a major focus in 2023. Several studies were conducted by the DEMO Central Team to define the optimum EU-DEMO design space, which is heavily constrained by physics and technology, aiming to minimise either the machine size or the technical risks. This included the assessment of the impact of varying certain stakeholder requirements, such as electricity output and pulse duration; the impact and associated risks of using high-field toroidal magnets, benefiting from promising high temperature superconductors; and machine configurations at low aspect ratio. The feasibility study of a volumetric neutron source has started aiming at completion by October 2024.
Lower aspect ratio configuration studies revealed that the plasma volume is not significantly affected when reducing the aspect ratio, however, the reattachment heat flux and magnetic field were reduced, leading to a new low aspect ratio baseline variant shown in Fig. 1. It was shown that reducing the electricity output from 500 MW to 100 MW, the device major radius drops by only 10% from 8.8 m to 8.0 m. On the other hand, increasing the duration of the pulse, keeping constant the net electricity power and accumulated neutron fluence, the major radius increases because the size of the central solenoid increases due to the required larger flux swings. It should also be noted that at very low pulse lengths i.e. below 1.5 hours, the size increases because of fatigue considerations, requiring thicker structures for the central solenoid.
During the JET Deuterium-Tritium experiments, a new fusion energy world record (69 MJ) was achieved in a single plasma pulse sustained for 5 seconds. Here, about 3 times more energy was injected to heat the plasma than was produced. The 69 MJ of energy was released from only 0.21 milligrams of a mix of 50-50% Deuterium and Tritium fuel. In the W7-X Stellarator a plasma discharge of 8 minutes with a record 1.3 GJ of injected energy was achieved.
Studies with varying magnetic field strengths concluded that increasing the magnetic field does not lead to a reduction in machine size, if the EU-DEMO requirements are considered, limiting the benefit of using high temperature superconductors as shown in Fig. 2. This is due to the large structures needed to withstand the electromagnetic forces, thick blanket and neutron-shield structures needed to protect the coils from radiation damage effects, and new divertor solutions required beyond present-day capabilities. Nevertheless, high temperature superconductors still offer certain benefits including the simplification of the magnet cooling scheme thanks to the increased temperature margin, which can simplify coil construction and minimize high-voltage risks at the terminals.
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Studies with varying magnetic field strengths concluded that increasing the magnetic field does not lead to a reduction in machine size, if the EU-DEMO requirements are considered, limiting the benefit of using high temperature superconductors as shown in Fig. 2. This is due to the large structures needed to withstand the electromagnetic forces, thick blanket and neutron-shield structures needed to protect the coils from radiation damage effects, and new divertor solutions required beyond present-day capabilities. Nevertheless, high temperature superconductors still offer certain benefits including the simplification of the magnet cooling scheme thanks to the increased temperature margin, which can simplify coil construction and minimize high-voltage risks at the terminals.
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