Metrosil meets stringent type test requirements at KEMA for Italian national fusion tokamak DTT.

To effectively manage the substantial energy contained within superconducting magnets, especially during quench events, Tokamak magnetic systems need to be equipped with extremely robust protection mechanisms.

In a pioneering move within the realm of Fusion Research, DTT (Divertor Tokamak Test Facility) has introduced Metrosil world leading brand of silicon carbide (SiC) varistors, marking a significant advancement in high energy quench protection. These matched banks of patented semiconducting power varistor tiles will form a critical part of the 3 x FDU, Fast Discharge Units used to protect the 18 x superconducting toroidal field coils.

Matched sets of Metrosil varistor units will be switched in by the custom power electronics of the FDU’s at Frascati Coil Cold Test Facility (FCCTF), to rigorously assess DTT’s superconducting coils and their associated FDUs under cryogenic conditions and at full operational currents and energies before being put into service.

Prior to integration into the cold test facility in Frascati a representative section of Metrosil varistor units underwent meticulous electrical testing at an independent laboratory (KEMA CESI Berlin, Germany). Representatives from the DTT Consortium, M&I Materials Metrosil Division, Manchester, UK and the FDU manufacturer OCEM, Bologna, Italy are collaborating closely throughout this project See (Fig. 2).

During testing, this section of Metrosil varistors, designed for nominal values of 42.5 kA and 85 MJ, were subject to peak currents ranging from 49 kA to 58 kA, and absorbed energies up to 92 MJ. As well as other temperature sensors placed across the system a visual representation of the uniform temperature distribution during testing is shown in Fig. 3.

The comprehensive type testing campaign at KEMA not only affirmed the efficacy of the protective measures Metrosil offers but also facilitated refinements in design and installation protocols, contributing to the overall robustness of the final FDU protection system for the DTT, and the TF Coils 2GJ discharge requirement.

Fig.1. Custom built steel frame with sliding drawers and busbar system supporting 32 matched units of 18 tile patented Metrosil varistors assembled by both OCEM Power Electronics and M&I Materials, Metrosil personnel  at KEMA CESI Laboratory in Berlin.

Fig. 2. DTT, OCEM, Metrosil and KEMA representatives in the test laboratory, Metrosil varistor system in the background.

Fig. 3. Uniform thermal  image  following the final  peak current test.