A novel design of Ohmic Transformer Power Supply (OTPS) for Spherical Tokamaks

Nuclear fusion is one of the few sustainable options to replace fossil fuels as the world's primary energy source, with Deuterium and Tritium as fusion fuels.Thich can be achieved by intersection of fusion science and power electronics in fusion reactors called Tokamak. Spherical Tokamak (ST) are low aspect Ratio Fusion Reactors with promising vital features such as improved plasma stability, better confinement, and higher power output than traditional Tokamaks. Ohmic Transformer Power Supply (OTPS) generates a high current derivative in the Ohmic field coils, which induces emf through transformer action and leads to gas breakdown, plasma current initiation, and plasma current ramp-up by producing sufficient ramp voltage in each stage. This paper proposes a capacitor-based novel design of OTPS in which the coil current slope is controlled using a multilevel H-Bridge topology. IGBTs and Thyristor have been used in this topology as switching devices. The fast controlled discharging of the capacitor has been achieved by switching three cascaded H-Bridge inverters. This will provide plasma initiation in Tokamaks through high di/dt in the range of 3-4 MA/s. The controlled action of coil current is achieved using the digital signal processor (DSP). Low pass LC filter has been used to reduce the ripple in coil current; this increases the complexity but counters the non-uniform loop voltage profile issue. This topology can produce a different loop voltage profile, which can enable to achieve different operational objectives.