• S. Matsubara, A. Higashiya, H. Maesaka, T. Ohshima, Y. Otake, T. Shintake, H. Tanaka, K. Togawa, M. Yabashi
  RIKEN/SPring-8, Hyogo
• H. Ego, S. Inoue, K. Tamasaku, T. Togashi, H. Tomizawa, K. Yanagida
  JASRI/SPring-8, Hyogo-ken

We re­port the de­sign, per­for­mance, and in­stal­la­tion of the beam di­ag­nos­tic sys­tem of XFEL/SPring-8. The elec­tron beam bunch­es of an XFEL ac­cel­er­a­tor are com­pressed from 1 ns to 30 fs by bunch com­pres­sors with­out emit­tance growth and peak-cur­rent fluc­tu­a­tion which di­rect­ly cause SASE fluc­tu­a­tion. To main­tain the sta­ble bunch com­pres­sion pro­cess, the ac­cel­er­a­tor re­quires rf caiv­ty beam po­si­tion mon­i­tors (BPM) with 100 nm res­o­lu­tion, OTR screen mon­i­tors (SCM) with a few mi­cro-me­ter res­o­lu­tion, fast beam cur­rent mon­i­tors (CT) and tem­po­ral struc­ture mea­sure­ment sys­tems with res­o­lu­tion under pi­cosec­ond. The per­for­mance of the de­vel­oped mon­i­tor in­stru­ments, such as the BPM, the SCM, and the CT, was test­ed at the SCSS test ac­cel­er­a­tor and sat­is­fied with the re­quire­ments. To mea­sure the tem­po­ral struc­ture of the elec­tron bunch, three type mea­sure­ment sys­tems, which are a streak cam­era, an EO sam­pling mea­sure­ment, and a trans­verse de­flect­ing cav­i­ty with a res­o­lu­tion of few-tens fem­tosec­ond, are being pre­pared. The streak cam­era and EO sam­pling shows the res­o­lu­tion of sub-pi­cosec­ond. The in­stal­la­tion of these beam di­ag­nos­tic sys­tems is going on smooth­ly.

• N. Hosoda, H. Maesaka, S. Matsubara, T. Ohshima, Y. Otake, K. Tamasaku
  RIKEN/SPring-8, Hyogo
• M. Musha
  University of electro-communications, Tokyo

The in­ten­si­ty of SASE gen­er­at­ed by un­du­la­tors is sen­si­tive to the peak in­ten­si­ty fluc­tu­a­tion of an elec­tron bunch. The bunch is formed by ve­loc­i­ty bunch­ing in an in­jec­tor and mag­net­ic bunch­ing in bunch com­pres­sors (BC). The peak in­ten­si­ty is sen­si­tive to rf phase and am­pli­tude of off-crest ac­cel­er­a­tion at in­jec­tor cav­i­ties and 5712 MHz cav­i­ties be­fore the BCs. Thus, de­mand­ed sta­bil­i­ties of the rf phase and am­pli­tude for sta­ble SASE gen­er­a­tion are very tight. These are 0.6 de­gree (p-p) and 0.06 % (p-p) at the 5712 MHz cav­i­ties, re­spec­tive­ly. We are con­struct­ing a low-lev­el rf (LLRF) sys­tem com­pris­ing a mas­ter os­cil­la­tor, an op­ti­cal rf sig­nal trans­mis­sion sys­tem, and a dig­i­tal rf con­trol sys­tem using IQ mod­u­la­tor/de­mod­u­la­tor to drive klystrons. To re­al­ize the de­mands, much at­ten­tion was paid to tem­per­a­ture sta­bi­liza­tion for the sys­tem. A wa­ter-cooled 19-inch rack and a wa­ter-cooled cable ducts are em­ployed for al­most all part of the sys­tem. Tem­per­a­ture sta­bil­i­ty of the rack was 0.4 K (p-p) even though out­side was 4 K (p-p). The phase and am­pli­tude sta­bil­i­ties of the LLRF mod­ules were mea­sured to be 0.30 de­gree (p-p) and 0.56 % (p-p). These sta­bil­i­ties are suf­fi­cient for our de­mands.