Design of spheromak injector using conical accelerator for Large Helical Device

Optimization of CT injector for LHD has been carried out and conical electrode for adiabatic CT compression is adopted in the design. Point-model of CT acceleration in a co-axial electrode is solved to optimize the electrode geometry and the power supplies. The condition to attain the large acceleration efficiency is researched and it is shown to be a function of the ratio of the electrode inductance to the external inductance. Acceleration efficiency of 34% is to be obtained with 3.2 m long conical accelerator and 40 kV–42 kJ power supply. The machine overview of a CT injector named SPICA Mk.I (SPheromak Injector using Conical Accelerator) consisting of 0.8 m conical accelerator is also given.