The purpose of this work is to study the 4H-SiC epitaxial layer properties for the fabrication of a device for neutron detection as an alternative material to diamond detectors used in this field. We have studied a high growth rate process to grow a thick epitaxial layer (250 µm) of 4H-SiC and, in order to estimate the quality of the epitaxial layer, an optical characterization was done through Photoluminescence (PL) spectroscopy for stacking fault defect evaluation. Micro Raman spectroscopy was used for simultaneous determination of both carrier lifetime and induced carriers in equilibrium. We have compared these results with other two samples with an epitaxial layer of 100 micron, obtained with two different growth rates, 60 and 90 µm/h, respectively. From Raman measurements it has been observed that both the growth rate and the grown epitaxial layer thickness have an effect on the measured carrier lifetime. A comparison between different kinds of stacking faults (SF) was done, evaluating the influence of these defects on the carrier lifetime as a function of the injection level and it was observed that only at a low injection is the effect on the carrier lifetime low.

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.

In this article, we report the results from two test campaigns conducted to evaluate the feasibility of implementing a commercially available optical fiber-based distributed sensing technology for Quench Detection (QD) purposes. We successfully characterized the temperature response and sensitivity achievable by this technique when using a bare single mode fiber within a cryogen free cooling system operating in the temperature range from 4 K to 300 K. A fiber was also incorporated into a sample featuring an High-Temperature Superconductor (HTS) stack mounted onto an extruded Aluminum slotted-core cable. Quench-like events were triggered by locally lowering the critical current using the magnetic field produced by a set of permanent magnets placed near the center of the stack. The experiments were carried out at 77 K by cooling the sample through the central channel of the Aluminum core with a forced flow of liquid nitrogen. The test results indicate the viability of this technology as a suitable alternative for QD in long-length HTS cables and motivate further work to develop distributed sensing systems able to work in the conditions foreseen for HTS fusion coils.

The use of wide-band-gap solid-state neutron detectors is expanding in environments where a compact size and high radiation hardness are needed, such as spallation neutron sources and next-generation fusion machines. Silicon carbide is a very promising material for use as a neutron detector in these fields because of its high resistance to radiation, fast response time, stability and good energy resolution. In this paper, measurements were performed with neutrons from the ISIS spallation source with two different silicon carbide detectors together with stability measurements performed in a laboratory under alpha-particle irradiation for one week. Some consideration to the impact of the casing of the detector on the detector’s counting rate is given. In addition, the detector response to Deuterium-Deuterium (D-D) fusion neutrons is described by comparing neutron measurements at the Frascati Neutron Generator with a GEANT4 simulation. The good stability measurements and the assessment of the detector response function indicate that such a detector can be used as both a neutron counter and spectrometer for 2–4 MeV neutrons. Furthermore, the absence of polarization effects during neutron and alpha irradiation makes silicon carbide an interesting alternative to diamond detectors for fast neutron detection.

The aim of this work was a deep spectroscopical characterization of a thick 4H SiC epitaxial layer and a comparison of results between samples before and after a thermal oxidation process carried out at 1400 °C for 48 h. Through Raman and photoluminescence (PL) spectroscopies, the carrier lifetimes and the general status of the epilayer were evaluated. Time-resolved photoluminescence (TRPL) was used to estimate carrier lifetime over the entire 250 µm epilayer using different wavelengths to obtain information from different depths. Furthermore, an analysis of stacking fault defects was conducted through PL and Raman maps to evaluate how these defects could affect the carrier lifetime, in particular after the thermal oxidation process, in comparison with non-oxidated samples. This study shows that the oxidation process allows an improvement in the epitaxial layer performances in terms of carrier lifetime and diffusion length. These results were confirmed using deep level transient spectroscopy (DLTS) measurements evidencing a decrease in the Z_1/2 centers, although the oxidation generated other types of defects, ON1 and ON2, which appeared to affect the carrier lifetime less than Z_1/2 centers.

The high environmental electromagnetic noise characteristic of fusion reactors and low quench propagation velocity of HTS conductors designed for such applications drive the quest for quench detection solutions alternative to voltage methods. Techniques based on optical fiber sensors represent a promising solution, but their integration in cables is not straightforward due to their intrinsic fragility. In this work, we report on the production and testing of an HTS aluminum slotted core cable exploiting a BRAided STack (BRAST) of REBCO tapes. The braid also encloses two stainless steel capillaries containing fiber-optic sensors responsible for monitoring the stack temperature. The sample was subjected to quench experiments at liquid nitrogen temperature, evaluating its electrical and thermal response. The experimental results demonstrate that the integration of optical sensors within the BRAST enables monitoring of stack temperature and detection of quench events, highlighting the greater sensitivity achieved by detecting temperature changes directly on the superconducting stack compared with sensors placed on the outer jacket. This approach represents thus a simple and effective solution for the integration of optical sensors in fusion cables.