Effect due to RF discharge from a high intensity H ion source upon the extracted beam

Shinto, Katsuhiro   ; Shibata, Takanori*; Wada, Motoi*

In J-PARC, peak H current of several tens mA is extracted from an ion source driven by a solid-state rf amplifier with the frequency of 2 MHz for production of a cesiated hydrogen plasma. In case of the rf-driven ion source for producing the high-intensity H current, the plasma density in the source chamber is so high that the ion sheath around the beam extraction area can follow the rf oscillation. The H beam current fluctuation as large as approximately 1 mA was observed at the average beam current of 44 mA measured by a Faraday cup installed downstream of the ion source. The beam exhibited some fluctuation to the transverse motion as well. To further clarify this high frequency oscillation of the beam extraction sheath, we propose a measurement system using a time-resolved and highly sensitive emittance monitor in order to observe the real-time beam fluctuation in the phase space.