Bunch shape monitor for the high-intensity H beam with 3 MeV using the carbon material

Kitamura, Ryo   ; Futatsukawa, Kenta*; Hayashi, Naoki  ; Hirano, Koichiro  ; Kosaka, Satoshi*; Miyao, Tomoaki*; Moriya, Katsuhiro  ; Nemoto, Yasuo*; Oguri, Hidetomo  

The longitudinal measurement and tuning at the beam transport after the RFQ are important to reduce the beam loss and the emittance growth in the J-PARC linac, when the high-intensity H beam of more than 60 mA is supplied. The new bunch shape monitor (BSM) using the carbon-nanotube (CNT) wire is necessary to measure the bunch shape of the high-intensity H beam with 3 MeV, because the CNT wire has a high-temperature tolerance and a small energy deposit. However, when the high voltage was applied to the CNT wire to extract the secondary electron derived, the discharge prevents the power supply from applying the voltage. Therefore, the discharge should be suppressed to measure the bunch shape with stability. Considering the characteristics of the CNT as the emitter, when the length of the CNT wire was short, the high voltage of -10 kV was applied to the CNT wire. The current status and future prospects of the BSM using the CNT wire are reported in this presentation.