• Y. Watanabe
  JAEA, Ibaraki-ken

In J-PARC RCS, horizontal closed orbit distortion (COD) which is ±2 or 3mm in amplitude was observed all over the ring. Main component of the horizontal COD is 1kHz, phase variation period about 140 seconds. This paper demonstrates phase variation of the 1kHz horizontal COD caused by switching ripple from dipole magnet power supply. To suppress the phase variation of the horizontal COD, switching timing of the dipole magnet power supply was synchronized J-PARC timing system.

• M. Watanabe, J. Kamiya, K. Suganuma, T. Takayanagi, N. Tani, T. Togashi, T. Ueno, Y. Watanabe
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

3 GeV rapid cycling synchrotron (RCS) of J-PARC accelerates proton beams from the 181 MeV up to 3 GeV. The RCS injects the beam to the Main Ring and transports it to the muon production target and neutron production target in the Materials and Life Science Experimental Hall. Proton beams in the RCS are fast extracted by kicker magnets at the repetition rate of 25 Hz. The rise time of the magnetic field is approximately 260 ns due to the propagation time through the coaxial cable and the kicker magnet itself. The flat-top length of it is required to 840 ns in order to extract two beam bunches. Pulse forming lines (PFL) and thyratrons are used to make the rise time and the flat-top, at the maximum charging voltage of 80 kV. Two thyratrons, which is a CX1193C made by e2V Ltd., are used for a power supply. 16 thyratrons are used in the eight power supplies of the kicker system. Since thyratrons are gaseous discharge switching devices, they often make misfire or self-breakdown in several hours. In this paper, present status of operation and voltage adjustment method of the reservoir and cathode heater power supply of the thyratrons in the kicker system are described.

• 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.

• T. Higo, T. Abe, M. Akemoto, S. Fukuda, N. Higashi, Y. Higashi, N.K. Kudo, S. Matsumoto, T. Shidara, T. Takatomi, K. Ueno, Y. Watanabe, K. Yokoyama, M. Yoshida
  KEK, Ibaraki

Under the CERN-SLAC-KEK collaboration, we have been developing the high gradient TW accelerator structures. One of the main focuses is the feasibility study of CLIC accelerator structure at X-band. A high power facility, Nextef*, was established at KEK in 2007. A few structures have been tested, including an un-damped disk-loaded structure successfully tested beyond 100 MV/m, a heavily damped structure to be tested from late 2009 and a structure made in a quadrant configuration. These structures follow the same accelerating-mode RF parameter profile, called CLIC-C**, but show different features at high gradient operation. Various observables, such as dark current, vacuum activities, light emission, breakdown rate, and so on, are measured. We discuss the high gradient phenomena related to these observables and the possible improvement for stable operation at a higher gradient.

* T. Higo et al., THP038, LINAC06,2006.
**A. Grudiev, http://indico.cern.ch/conferenceDisplay.py?confId=30911

• 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.

• Y. Sato, M.K. Fujimaki, N. Fukunishi, A. Goto, Y. Higurashi, E. Ikezawa, O. Kamigaito, M. Kase, T. Nakagawa, J. Ohnishi, H. Okuno, H. Watanabe, Y. Watanabe, S. Yokouchi
  RIKEN Nishina Center, Wako

The RI beam factory at RIKEN Nishina Center needs high intensity of uranium ion beams. We constructed a new injector, RILAC2, which would provide several hundred times higher intensity. As a part of the RILAC2, we designed the low energy beam transport, LEBT, from the superconducting ECR ion source to the RFQ entrance. In this paper we present its requirements and problems, and show our design as the solutions to them. Especially we focus a technique of a pair of two solenoids to treat a rotational operation and a focusing operation independently. Based on this design, the LEBT was completed in March 2010. The RILAC2 will be operational this fall.

• Y. Sato, M.K. Fujimaki, N. Fukunishi, A. Goto, Y. Higurashi, E. Ikezawa, O. Kamigaito, M. Kase, T. Nakagawa, J. Ohnishi, H. Okuno, H. Watanabe, Y. Watanabe, S. Yokouchi
  RIKEN Nishina Center, Wako

The RI beam factory at RIKEN Nishina Center needs high intensity of uranium ion beams. We have used so far the RFQ pre-injector upstream of the linac system, in which the extraction voltage of the ECR ion source is as low as 5.7 kV for the uranium beam. However, for much higher intensity beams from a newly developed superconducting ECR ion source, such a low voltage was expected to significantly increase their emittance due to the space charge effect. To reduce this effect, we prepared a new pre-injector line of 127 kV for uranium beams by placing the ion source on a high-voltage terminal. In this paper we present the design of the 127 kV medium energy beam transport, MEBT, and show the measured results through the line.

• Y. Higurashi, M.K. Fujimaki, A. Goto, E. Ikezawa, O. Kamigaito, M. Kase, M. Komiyama, T. Nakagawa, J. Ohnishi, Y. Watanabe
  RIKEN Nishina Center, Wako
• T. Aihara, M. Tamura, A. Uchiyama
  SHI Accelerator Service Ltd., Tokyo

The next generation heavy ion accelerator facility, such as the RIKEN RIBF, requires great variety of high charged heavy ions with a magnitude higher beam intensity than currently achievable. In the last decade, performance of the ECR ion sources has been dramatically improved with increasing the magnetic field and RF frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key components (magnetic field configuration, gas pressure etc) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and the technology, we successfully constructed the new 28GHz SC-ECRIS which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. In the test experiment, we obtained the direct evidence that the field gradient and the zone size strongly affect the beam intensity. It concludes that the gentler field gradient and large ECR zone size gives intense beam of highly charged heavy ions from ECR plasma. In this contribution, we report the systematic study of these effects on the beam intensity of highly charged heavy ions.