EUROfusion

Accurate models of the scrape-off layer are required for the design and operation of tokamak fusion reactors. Scrape-off layer simulations are computationally expensive, difficult to operate and suffer from numerical instabilities. A potential remedy comes in using machine learning models trained on simulations for fast and easy to use predictions. We present a such candidate surrogate model - named SOLPS-NN - to provide recommendations for the methods to construct it. Based on a large dataset of several thousand SOLPS-ITER simulations with reduced neutral fidelity, a variation of machine learning models with differing architectures and scopes are tested. The evaluation shows that simple fully connected neural networks are a suitable architecture. It is demonstrated that the whole spatial domain can be predicted at once, but that it is easier to achieve high accuracy by employing independent models for different observables. The presented surrogate model with reduced neutral fidelity is sufficient to predict access to detachment with trends similar to experiments. A small dataset of higher fidelity ITER baseline SOLPS-ITER simulations is used to (re-)train surrogate models. The smaller extent of the ITER dataset allows for achieving much more accurate predictions. Transfer learning from the previous surrogate model works but has no direct benefits over training a new model from scratch. Future efforts should focus on discovering the potential and the methods for models utilizing simulations with mixtures of fidelity.

Gyrokinetic (GK) stability strongly influences the performance of high-confinement-mode pedestals in spherical tokamak plasmas. High-fidelity gyrokinetic codes such as GENE can model microinstability-driven transport, but the computational cost limits their routine use in integrated pedestal modeling workflows. Instead, present workflows often rely on reduced transport assumptions, such as the ballooning-critical pedestal model used in EPED. This work investigates machine-learning surrogate models for local linear gyrokinetic simulations in a MAST-U-relevant pedestal parameter space, with the aim of providing faster gyrokinetic-based inputs to reduced pedestal models. A sampling workflow is developed in which pedestal profile parameters are varied within experimentally motivated bounds and used to generate physically self-consistent Grad-Shafranov equilibria. This reduces the dimensionality of the data-generation problem compared with sampling local gyrokinetic inputs directly, while maintaining physically plausible combinations of plasma profiles, geometry, and local stability parameters. The surrogate models are trained to predict linear growth rates, real frequencies, and diffusivity-ratio transport fingerprints from local linear GENE simulations. A multi-head multilayer perceptron accurately reproduces the growth rate, while the diffusivity ratios and real frequency exhibit more clustered, regime-dependent behavior. A multi-head classification-regression model using frequency-based regime classes reduces the mean absolute error for these clustered targets and better captures sharp transitions associated with changes in the underlying instability regime, although errors near mode-transition regions remain a limitation.

The Engineering Validation and Engineering Design Activities for the International Fusion Materials Irradiation Facility (IFMIF/EVEDA) project have been conducted as one of the three projects (IFMIF/EVEDA, IFERC and JT60SA) within the Broader Approach (BA) agreement between EURATOM and the Japanese government since 2007. The IFMIF is intended to deliver accelerator-based deuterium-lithium (D-Li) neutrons at energies and intensities sufficient to enable the qualification of candidate materials for future fusion energy reactors, such as DEMO. The primary objective of the IFMIF/EVEDA project is twofold: (i) to develop a detailed engineering design of the IFMIF and (ii) to validate its major components, namely the accelerator facility, the lithium target facility and the test facility. During Phase I of the BA, which concluded in March 2020, the engineering validation activity (EVA) for the lithium target facility and the test facility were successfully completed through the construction and testing of prototypes. In contrast, the EVA for the accelerator facility, implemented through the Linear IFMIF prototype accelerator (LIPAc), remains on-going. The current phase (Phase II) focuses on the continued commissioning of the LIPAc and the enhancement of some sub-systems to support the development of the Fusion Neutron Source Design (FNSD). This article presents an overview of the progress achieved in the LIPAc commissioning and FNSD activities and outlines the future directions of the activities.

The electron cyclotron (EC) system is critical for heating and controlling the fusion plasma. The system foreseen for installation in the equatorial port of the EU-DEMO reactor will be exposed to intense neutron irradiation, making activation, maintenance, and waste classification key design constraints. This study analyses the neutronic response and activation of the main EC components using MCNP to calculate neutron fluxes, energy spectra, and nuclear heating. It also includes FISPACT-II calculations of activation inventories, decay heat, contact dose rates, and dominant radionuclides. The results, assessed over relevant cooling times, show that stainless-steel components located closest to the plasma exceed low-level waste (LLW) limits even after extended cooling periods, whereas inner and rear components exposed to lower neutron fluxes generally meet LLW criteria. Dominant long-lived radionuclides have been identified to support waste classification and disposal planning. These findings provide essential guidance on material selection, waste minimisation, shielding and cooling design, and interim storage strategies, supporting the safe integration of the EC system within the DEMO reactor.

Abstract The main scientific purpose of JT-60SA is to complement ITER in the preparation of the operation of a DEMOnstration fusion reactor, in particular investigating the conditions for a controllable high-beta steady-state regime able to optimise the fusion gain. In order to accomplish this task, a sequence of operation and machine enhancement periods in the next few years are planned to reach the target performance of the machine before a transition to a full tungsten wall. EUROfusion and Fusion for Energy are jointly contributing to the enhancement plan of JT-60SA, in particular, with regard to the present contribution, to provide JT-60SA with state-of-the-art diagnostics in support of its scientific and technical objectives. This paper reports the status of the projects being implemented in view of the next scientific campaigns or under consideration through the various stages from feasibility to detailed design.