Compact fusion reactors require high temperature superconductors (HTS) for the production of high field magnets capable of confining the plasma and achieving enough fusion power to reach commercial interest. The generation of high energy neutrons in the plasma, together with the consequent proliferation of secondary particles, threatens the long term performance of the HTS materials due to the heat load and radiation damage. For this reason it is crucial to develop tools for the comprehensive simulation of radiation environment and effects throughout the reactor structure. Here we present Monte Carlo simulations of an ARC-like reactor yielding the neutron and secondary particles spectra, the power deposition, and the materials damage mapped over the whole system, focusing on the effects on the toroidal field and poloidal field HTS coils. We find that the peak of the heat deposition in the magnets is located near the divertor, and that a strongly non-homogeneous distribution of damage urges the geometrical optimization of neutron shields.

The development of compact fusion reactors relies on high temperature superconductors to generate the required high field. In this frame Rare-Earth Barium Copper Oxide tapes appear as the most promising solution. However, these tapes will experience a radiation harsh environment due to the high flux and fluence of energetic neutrons and of the secondary particles produced by the neutrons interaction with the materials. Realistic 3D Monte Carlo simulations represent the required tool to reliably estimate the radiation environment of the tapes, providing the starting point for experimental investigation of their radiation hardness and performance under working conditions. In this paper a comprehensive analysis of damage and energy deposition including secondary particles on a 3D model of a VIPER cable is carried out, starting from a 3D model of an ARC-class reactor.

High-temperature superconducting-slotted cables, including the VIPER cable, are being investigated as possible candidates for winding the toroidal field coils of compact nuclear fusion machines, such as ARC. The higher performance of HTS materials in terms of magnetic fields and currents allows them to reduce their size compared to machines based on Nb alloys and compounds. However, compactness also means a closer interaction between the plasma products and the coils, creating new technological challenges to be faced. Among the others, the thermal effects induced on the superconducting materials by direct particles (i.e., neutrons), secondary particles and gamma-ray heating, will be stronger than for low-field larger machines and must be quantified. In this paper, a detailed thermo-magnetic model is built up using the software COMSOL Multiphysics to simulate the consequences of the D-T plasma operation products on the first turn of a toroidal field coil of the ARC preliminary machine design. The irradiation-induced heat load on the (RE)Ba ₂ Cu ₃ O _7-δ tapes, computed via Monte Carlo simulations, is used as input for the thermal analysis of the VIPER cable. At the same time, a homogenized T-A formulation is developed for checking the performance reduction in the current/field operating conditions.

Compact fusion reactors are receiving increasing interest as a promising route for accelerating the path toward commercial fusion, thanks to their reduced size and cost. However, this compactness introduces new technological challenges, including higher radiation loads on critical functional components, such as the magnet system. Neutron shielding is therefore of utmost importance to guarantee the expected lifetime of the device, and its selection must account for the harsh environment imposed by the high radiation flux. Shielding materials should be structurally stable, not melt within the operational temperature windows, and be relatively low-cost. For nuclear reactor applications, binary compounds are typically the preferred choice as they often meet these requirements, particularly in terms of availability and cost. In this work, we present a systematic Monte Carlo analysis of more than 700 binary compounds, exposed to the neutron spectrum at the most loaded position of the vacuum vessel in a simplified model of a compact fusion reactor. Shielding performances were evaluated in a toroidal geometry in terms of neutron attenuation, power deposition, and activation, leading to the identification of several promising compositions for effective neutron shielding in future fusion applications.