• Y. Takeda, Y. Irie, H. Kawakami, M. Oyaizu, I. Sugai, A. Takagi
  KEK, Ibaraki
• T. Hattori, K.K. Kawasaki
  TIT, Tokyo

Japan Proton Accelerator Research Complex (J-PARC) requires thick carbon stripper foils (200-500 ug/cm²) to strip electrons from the H^- beam supplied by the linac before injection into the Rapid Cyclic Synchrotron. A H^- beam of 181MeV energy is injected into the 3 GeV Rapid Cycling Synchrotron (RCS) with a pulse length of 0.5 ms, a repetition rate of 25 Hz, and an average beam current of 200 μA. The H^- ions are stripped into protons by a charge stripper foil in the injection section. For this high-energy and high-intensity beam, the conventional carbon stripper foils will be ruptured in a very short time. Thus, long-lived thick carbon stripper foils are needed to this high-power accelerator. For this purpose, we are described R and D of long-lived Hybrid Boron-mixed Carbon foils (HBC-foils) of 100 - 500 μg/cm² by arc discharge method. The preparation procedure is described and lifetime measurement by using a 3.2MeV Ne⁺ DC beam of 2-3 μA are reported.

• H. Fujimori, Z. Igarashi, Y. Irie, Y. Sato, M.J. Shirakata, I. Sugai, A. Takagi, Y. Takeda
  KEK, Ibaraki

The carbon stripping foil is the key element for the high-intensity proton accelerator. At KEK, the foil test system using the 650keV H^- Cockcroft-Walton accelerator is in operation, which can simulate the energy depositions to the foil with the same amount in the J-PARC. In order to quantatively observe the foil degradations (such as foil thinning, pin-hole production) during irradiation, online energy and particle analyzing system is under construction. This report outlines the design detail of the analyzing system including the detectors.

• A. Takagi, Y. Irie, I. Sugai, Y. Takeda
  KEK, Ibaraki

Thick carbon foils (>300ug/cm²) has been used for stripping of H^- ion beam into protons at the injection stage of the 3GeV Rapid Cycling Synchrotron (3GeV-RCS) in J-PARC. The carbon stripping foils with high durability at high temperature >1800K are strongly required. We have recently developed a new irradiation system for lifetime measurement of the stripping foils using the KEK 650keV Cockcroft-Walton type of high voltage accelerator with high current pulsed negative hydrogen ion beam, which can simulate the high energy-depositions upon foils in the RCS. It is found that, by adjusting the peak intensity and the pulse length of the hydrogen ion beams appropriately, the energy deposition becomes equivalent to that exerted by the incoming hydrogen ions and the circulating protons at the injection process of the RCS. The most important factor that affects the foil lifetime is the foil temperature. During lifetime tests by this system, the temperature of foil is measured by a fast thermometer and by using a phototransistor in a pulsed mode (650keV, 10mA, 0.25msec, 25Hz). The new irradiation system and some preliminary results on lifetime of the carbon stripping foil will be presented.

• P.K. Saha, H. Harada, H. Hotchi, K. Yamamoto, Y. Yamazaki, M. Yoshimoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• I. Sugai
  KEK, Ibaraki

The beam loss caused by the nuclear scattering together with the multiple Coulomb scattering at the stripping foil is one of the key issue in RCS (Rapid Cycling Synchrotron) of the J-PARC (Japan Proton Accelerator Research Accelerator). In order to have a very realistic understanding, a systematic study with both experiment and simulation has been carried out recently. A total of seven targets with different thickness were used and the measured beam losses were found to be good in agreement with that in the simulation. A detail and realistic understanding from such a study will be very useful not only to optimize the foil system including the thickness and size at present with the injection beam energy of 181 MeV but also for the near future upgrade with 400 MeV and in addition can be a good example for similar existing and proposing projects.

• Y. Yamazaki, M. Kinsho, O. Takeda, M. Yoshimoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• I. Sugai
  KEK, Ibaraki

J-PARC requires thick carbon stripper foils to strip electrons from the H^- beam supplied by the linac before injection into the Rapid Cycling Synchrotron (RCS). Foil thickness is about 200 μg/cm² corresponding to conversion efficiency of 99.7% from the primary H^- beams of 181MeV energy to H⁺. For this purpose, we have successfully developed hybrid type thick boron-doped carbon (HBC) stripper foils, which showed a drastic improvement not only with respect to the lifetime, but also with respect to thickness reduction and shrinkage at high temperature during long beam irradiation. We started to study carbon stripper foils microscopically why carbon foils have considerable endurance for the beam impact by boron-doped. At first, we made a comparison between nominal carbon and HBC by the electric microscope and ion-induced analysis. In this paper, we will introduce some results for characteristics of HBC foils.

• M. Yoshimoto, H. Harada, N. Hayashi, H. Hotchi, Y. Irie, M. Kawase, M. Kinsho, R. Saeki, P.K. Saha, K. Yamamoto, Y. Yamazaki
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• T. Ishiyama
  KEK/JAEA, Ibaraki-Ken
• I. Sugai
  KEK, Ibaraki

The hybrid type thick boron-doped carbon (HBC) stripping foils are installed and used for the beam injection at the 3GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex). The HBC foils are developed by Sugai group in KEK, which improved the lifetime drastically. Up to now, the performance deterioration of the stripping foils can not be seen after the long beam irradiation for the 120kW user operation and 300kW high power beam demonstration at the RCS. In order to examine the characteristic of the HBC foils, various beam studies were carried out. The beam-irradiated spot at the foil was measured by scanning the foil setting position, the charge exchange efficiency was evaluated with various thickness foils, and the effect of the SiC fibers supporting the foil mounting was checked with different mounting foils. Beam study results obtained with using the HBC foils will be presented. In addition, the trends of outgas from the stripping foils and the deformations of the foils during the beam irradiation will be reported.