AbstractThis paper describes the JA home team design of the ITER ECRF power supply system whose capacity is 200 MVA. The system has 16 power supply units to drive 68 gyrotrons with total radio frequency power of 68 MW for plasma heating, current drive and plasma start-up. Each unit drives gyrotrons with energy recovery system to achieve higher than 50% of efficiency. The gyrotron fast protection system is based on a 70 kV, 100 A fast Insulated Gate Bipolar Transistor (IGBT) switch composed of 70 IGBTs connected in series. The breaking capability of this switch is 360 A with a protection time less than 10 μs. The estimated short circuit energy, in case of load fault, is 0.26 joule which is far below the allowable energy of 10 joule. The main power supply output voltage control is done by a.c. thyristor voltage regulator with state feedback control and feedforward control of beam current and voltage of the input a.c. line. In the layout design, the reduction of fire escalation risk is taken into account. The total space needed for the installation is 35 m×200 m for outdoor and 25 m×90 m for indoor.