Benefits of high-energy varistors in breakdown and fast discharge units

Tokamak coils require protection systems to extract the stored magnetic energy without breaking the power supply circuit. This is more critical in superconducting coils, especially due to quench phenomena. This protection can be simply obtained by fast discharge units (FDUs), able to insert proper resistor banks in the coil circuit. Similarly, resistive switching network units (SNUs) are the standard method to initiate plasma in tokamak. The use of varistors instead of linear resistors can introduce several benefits for the tokamak operations, including the possibility to implement in a single unit both the SNU and the FDU functions. These principles are descried in this paper with reference to their applications in the DTT facility, reporting some examples of the possible and selected parameters. Nevertheless, the proposed approaches, the developed theory and the obtained results can be adapted to any tokamak and nuclear-fusion project.