• K. Niki, H. Ishiyama, I. Katayama, H. Miyatake, M. Okada, Y. Watanabe
  KEK, Ibaraki
• S. Arai
  RIKEN Nishina Center, Wako
• H. Makii
  JAEA, Ibaraki-ken

The mea­sure­ment of 12C(alpha,gamma) re­ac­tion is planned at TRIAC(Tokai Ra­dioac­tive Ion Ac­cel­er­a­tor Com­plex). An in­tense pulsed alpha beam with the width of less 10ns and the in­ter­val be­tween 250ns and 500ns is re­quired for this ex­per­i­ment. Be­cause the Split Coax­i­al RFQ (SCRFQ), which is one of the TRIAC ac­cel­er­a­tors, has a radio fre­quen­cy of 26MHz, the bunch in­ter­val be­comes 38.5ns. In order to make the bunch in­ter­val of 250ns or more, the pre-bunch­er with a fre­quen­cy of 2-4MHz, is con­sid­ered to be in­stalled up­stream of the SCRFQ. It is de­signed as the pre-bunch­er has two gaps with non-Pi mode. In order to make the bunch­ing beam pro­file like a pseu­do saw­tooth-wave, the RF volt­age syn­the­sized three har­mon­ic fre­quen­cies is ap­plied to these gaps. Con­se­quent­ly, the pre-bunch­er has a com­pact size and no leak­age elec­tric field out­side gaps, and can keep the RF volt­age low. Re­cent­ly, the beam test of this pre-bunch­er with a case of 2MHz-RF and SCRFQ was per­formed by using 16O⁴⁺ and 12C³⁺ beams. The clear bunch struc­ture with a in­ter­val of 500ns was ob­tained by the SSD set down­stream of the SCRFQ. The re­sults of the beam test are al­most con­sis­tent with those of the beam sim­u­la­tion code.

• M. Okada, H. Ishiyama, I. Katayama, H. Miyatake, K. Niki, Y. Watanabe
  KEK, Ibaraki
• S. Arai
  RIKEN Nishina Center, Wako
• H. Makii
  JAEA, Ibaraki-ken

In TRIAC (Tokai Ra­dioac­tive Ion Ac­cel­er­a­tor Com­plex), in­tense bunched beams are planned for mea­sure­ments of 12C(alpha, gamma) re­ac­tions. For 2-4MHz bunch­ing to the 26MHz linac beams, saw­tooth-wave pre-bunch­er has been de­vel­oped. Since the wave ap­plied to the pre-bunch­er is pseu­do saw­tooth shape syn­the­sized from three sine waves, par­ti­cles in out-of-bunch phase be­come back­grounds to the bunched beams. In order to re­move them, a mul­ti­lay­er chop­per has been newly in­stalled up­stream the pre-bunch­er. The mul­ti­lay­er chop­per has 20 elec­trodes (40mm wide, 10mm long, and 0.1mm thick) piled up with gaps of 1.9mm in ver­ti­cal­ly to the beam di­rec­tion. And a square-shape elec­tric po­ten­tial (100V max­i­mum, 2-4 MHz) is ap­plied to each elec­trodes al­ter­nate­ly. The short gap makes it pos­si­ble to re­al­ize sharp beam-chop­ping with rel­a­tive­ly low elec­tric po­ten­tial and weak leak­age elec­tric field, al­though beam par­ti­cles could be lost by 5% or more, since this chop­per is set on the way of beams. As a re­sult, the ratio of bunched par­ti­cles to back­grounds has been im­proved from 3:1 to 99:1 by the chop­per. High in­ten­si­ty beam test by 16O⁴⁺ beam will be also re­port­ed.