• 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.