Perfectly matched pulsed 2MHz RF network and CW 30MHz RF matching network for the J-PARC RF-driven H~- Ion Source

摘要

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of an H~- ion beam current of 60mA within normalized emittances of 1.5πmm·mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of more than 50days, a cesiated RF-driven H~- ion source using a internal-antenna developed at the Spallation Neutron Source (SNS) was developed. As similar as the SNS ion source, the 60kW pulsed 2MHz-RF and 200W CW 30MHz-RF systems are used in order to produce pulsed high-temperature 2MHz-RF plasma and CW low-temperature 30MHz-RF plasma. Each matching network for each system is composed of two vacuum variable condensers (VVCs). In order to supply pulsed 60kW-2MHz-RF power from the power supply (PS) on the ground level, a one-turn isolation transformer using FINEMET cores is installed between the PS and the J-PARC ion source. By comprehending the matching networks with the LTspice IV simulations and high- and low- power experiments and setting the parameters properly, the pulsed 2MHz-RF power up to 46 kW is successfully input to the hydrogen plasma without any misfire and with almost no reflected power.