New Challenges in Nuclear Fusion Reactors: From Data Analysis to Materials and Manufacturing

Dear Colleagues,

A new and challenging period has recently started for the nuclear fusion community. In the new FP9 framework, we are called to provide, in the coming years, the physics and the engineering basis for the operational scenarios and exploitation of the next generation of magnetically controlled nuclear fusion devices, meaning for ITER and DEMO for the Tokamak community and HELIAS for the stellarator one. At the same time, the actual largest and most important tokamak in the world, JET, has approached a new T campaign, the first since 1997.

The already operational fusion reactors are nonlinear, complex and far from a stable equilibrium, with almost every physical parameter indirectly measured using a plethora of diagnostics. Routinely, they produce gigabytes of data that require dedicated storage systems and architectures. Modeling is a necessary step for the comprehension of the physical mechanism behind many experimental observations, but in many aspects, from control and classification to extrapolation and forecasting, statistical and machine learning approaches have been demonstrated to be fundamental.

In this multidisciplinary project, physical goals such as MHD and ELMs stable scenarios, disruption avoidance schemes based on verified chains of events, as well as the comprehension of the role of fast ions, impurities and isotopes mixtures on the plasma stability, regimes and transport are examples of open issues to be addressed in the coming years, in addition to managerial and engineering ones.

The design of diagnostics, control systems, international protocols and the quantification of costs have to be considered, but it is a matter of fact that the new generation of devices will be extremely challenging for materials.

Nuclear fusion reactors are extremely hostile environments for materials and plasma-facing components (PFC). ITER or DEMO will withstand severe steady-state thermal loads up to about 20 MW m⁻² combined with transient ones up to GW m⁻² due to edge-localized modes (ELMs). In addition, off-normal events such as the already cited disruptions or vertical displacement events (VDEs) could take place, compromising the mechanical integrity of the reactor. Thermally induced erosion of plasma-facing material (PFM) and damage of the joints between the PFM and the heat sink are to be considered; material irradiation with hydrogen isotope ions (D⁺ and T⁺) and impurities’ particles will create hydrogen-induced and neutron-induced degradation of the wall, transmutation, and activation. The appropriate choice of PFM, the design and the joining technique of PFC are a challenging issue for fusion reactors’ successful operation.

In this exciting framework, then, this issue calls for papers aimed at providing ideas, projects and discoveries elaborated in all the WP of the FP9 program to build the future and to stand as references for the coming years.

Contributions can be based on (but not limited to) the following fields:

• Diagnostics: design, applications, and development (for example, microwaves and millimeter-wave diagnostics, infrared polarimetry/interferometry, spectroscopic and radiation measurements, neutron/gamma diagnostics, laser diagnostics);
• Modeling;
• Inverse problems (for example, tomography, equilibria reconstruction);
• Data analysis and machine learning techniques;
• Plasma facing materials: their behavior under steady-state and transient heat loads, irradiation effects, tritium retention, joining techniques, etc.;
• Operational control scheme designs (for example, feedback and feedforward schemes);
• Managerial protocol and cost evaluation.

Dr. Emmanuele Peluso
Dr. Michela Gelfusa
Dr. Ekaterina Pakhomova
Guest Editors

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