• K. Yamada, S. Arai, M.K. Fujimaki, T. Fujinawa, N. Fukunishi, A. Goto, Y. Higurashi, E. Ikezawa, O. Kamigaito, M. Kase, M. Komiyama, K. Kumagai, T. Maie, T. Nakagawa, J. Ohnishi, H. Okuno, N. Sakamoto, Y. Sato, K. Suda, H. Watanabe, Y. Watanabe, Y. Yano, S. Yokouchi
  RIKEN Nishina Center, Wako
• H. Fujisawa
  Kyoto ICR, Uji, Kyoto

A new additional injector (RILAC2) is constructed at RIKEN Nishina Center in order to enable the independent operation of the RIBF experiments and super-heavy element synthesis. The RILAC2 consists of a 28 GHz superconducting ECR ion source, a low-energy beam transport with a pre-buncher, a four-rod RFQ linac, a rebuncher, three DTL tanks, and strong Q-magnets between the rf resonators for the transverse focusing. Very heavy ions with m/q of 7 such as ¹³⁶Xe²⁰⁺ and ²³⁸U³⁵⁺ will be accelerated up to the energy of 680 keV/u in the cw mode and be injected to the RIKEN Ring Cyclotron without charge stripping. The RFQ linac, the last tank of the DTL, and the bunchers have been converted from old ones in order to save the cost. Construction of the RILAC2 started at the end of the fiscal 2008. The RFQ and DTLs will be installed in the AVF cyclotron vault and be tested in March 2010. The ECR ion source and low-energy beam transport will be set on the RILAC2 in 2010 summer, and the first beam will be accelerated in 2010 autumn. We will present the details of the linac part of RILAC2 as well as the progress of construction which includes the result of high power test of resonators.

• K. Suda, S. Arai, Y. Chiba, O. Kamigaito, M. Kase, N. Sakamoto, K. Yamada
  RIKEN Nishina Center, Wako

A new injector RILAC2 for RIKEN RI-Beam Factory is under construction. The three Drift Tube Linac (DTL) cavities, located downstream of an RFQ linac, are designed to operate at a fixed RF frequency of 36.5 MHz, and to accelerate very heavy ions such as 136Xe²⁰⁺ and 238U³⁵⁺ from 100 keV/u to 680 keV/u for the injection to the RIKEN Ring Cyclotron. The first two cavities (DTL1 and 2) are newly constructed, and an existing cavity is modified for the last one (DTL3). The structure is based on the quarter-wavelength resonator. The inner diameter ranges from 0.8 to 1.3 m. In order to save the construction cost and space for the equipments, direct coupling scheme has been adopted for the RF amplifier. A capacitive coupler was designed to match the input impedance to 700, which corresponds to the optimum output impedance of a tetrode. Design of the cavities and couplers will be described in detail.

• 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.