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In the present configuration of the European demonstration nuclear fusion power plant (DEMO), the toroidal magnetic field is produced by 16 superconducting toroidal field (TF) coils. The total stored energy of 146 GJ, more than 3 times the energy stored in ITER TF coils, has to be quickly dissipated in case of quench by suitable Fast Discharge Units (FDU). The energy, the current and the discharge time constant define the voltage to be applied to the coils; however, the peak value at the coil terminals during the fast transient phase at the beginning of the discharge or in case of faults can be much higher. This paper deals with first studies addressed to estimate maximum voltage stresses on the coils in various operating and fault conditions and to evaluate the relative merit of different TF circuit topologies to support the design work, aimed at finding the best compromise between requirements for the coil insulation and cost and size of FDUs, busbars and current leads. Analyses and numerical simulations have been carried out, for both the cases of TF circuit composed of 16 and 8 sectors. The results are reported and discussed.

The Acceleration Grid Power Supply (AGPS) is a system devoted to supply the acceleration grids of the MITICA experiment, the full scale prototype of the ITER Neutral Beam Injector (NBI). The AGPS is a special switching power supply with demanding requirements: high rated power (about 55 MW), extremely high output voltage (-1MV dc), long duration pulses. The procurement of the AGPS is split in two parts: the low voltage conversion system, namely the AGPS-Conversion System (AGPS-CS) and the high voltage DC Generators (AGPS-DCG). The AGPS-CS has been installed and commissioned in between late 2017 and early 2018. The design of the installation engineering has been particularly challenging. Some critical issues concerning the integration with the existing buildings and auxiliary systems were assessed during the installation period. Examples of such issues are the definition of the medium voltage cable layout and interfaces, the design of high current busbars penetrating in the building for compatibility with the prescriptions about fire propagation, the adaptation of the infrastructures to enhance the maintainability of the system. Another important matter has been the assessment of the passive filters needed to damp the voltage oscillation at the end of the cables connecting the AGPS-CS to AGPS-DCG, which were demonstrated to be necessary after the analysis of the cabling layout. Concerning the commissioning and acceptance tests on site, they were performed on a dummy load at reduced power and duty, testing one section of the system at a time, being very difficult to design and realize a test at full rated power. This paper is focused on the installation and commissioning activities, highlighting the peculiar integration aspect of this unique system, above described. Moreover, the results of the site tests are presented, showing the ability of the system to provide the required performance.

In the European DEMOnstration nuclear fusion power plant (DEMO), the desired toroidal magnetic field is produced by a magnet system composed of 16 Toroidal Field (TF) coils, according to the last 2017 reference baseline. The total stored energy of about 140 GJ, more than three times that of ITER TF coils, has to be quickly dissipated in case of quench by a suitable Quench Protection (QP) system. The energy, the current and the required discharge time constant define the voltage to be applied to the coils; however, the peak value at the coil terminals during the fast transient phase at the beginning of the discharge or in case of faults can be much higher. This paper deals with first studies addressed to estimate maximum voltage stresses for TF coils in various operating conditions and for different TF circuit topologies to evaluate their relative merit and to provide inputs for the definition of the number of toroidal sectors as a compromise between requirements for the coil insulation and cost and size of protection system, busbars and current leads. The studies were firstly done with 18 TF coils (2015 reference baseline); since three different winding pack options are under study, we selected the one characterized by the highest inductance, thus by the related highest voltage across the coils at the discharge. Numerical simulations were carried out to reproduce the voltage waveforms at the coil terminals, across the coils and to calculate the i2t in the coils for the cases analyzed for the different TF QP circuit topologies, operating conditions, and number of sectors (18 / 9). Then, the analyses have been updated for the case of 16 / 8 sectors of the last reference baseline; all the main results are reported and discussed.