A 3D Particle-In-Cell calculation of J-PARC RF ion source; Effects due to near antenna electric field

Shibata, Takanori*; Nakano, Haruhisa*; Wada, Motoi*; Shinto, Katsuhiro   ; Okoshi, Kiyonori ; Nammo, Kesao*; Kawai, Isao*; Oguri, Hidetomo  

In the high-power proton accelerator facilities, Radio Frequency (RF) driven negative hydrogen ion (H) sources are adopted as particle sources for the maintenance-free duration over several months and for the stability of the H beam characteristics in the long-term operation. Techniques of RF plasma excitation are also introduced in the fusion field as ion sources of the neutral beam injection (NBI). On the other hand, the RF ion sources have a feature that the extracted beam current and phase space show slight oscillation with input RF frequency. The oscillation of the phase space may lead to mismatches of Twiss parameters or beam loss at the accelerator cavities in the higher-power beam operation. A 3D Particle-In-Cell (PIC) modeling based on Monte-Carlo collision was developed to elucidate the beam oscillation mechanisms. The presentation reports the effects upon the beam formation due to the electric potential fluctuation caused by a capacitive coupling to the internal antenna coil.