• 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

• T. Higo, Y. Higashi, S. Matsumoto, K. Yokoyama
  KEK, Ibaraki
• C. Adolphsen, V.A. Dolgashev, A. Jensen, L. Laurent, S.G. Tantawi, F. Wang, J.W. Wang
  SLAC, Menlo Park, California
• S. Döbert, A. Grudiev, G. Riddone, W. Wuensch, R. Zennaro
  CERN, Geneva

A CERN-SLAC-KEK col­lab­o­ra­tion on high gra­di­ent X-band ac­cel­er­a­tor struc­ture de­vel­op­ment for CLIC has been on­go­ing for three years. The major out­come has been the demon­stra­tion of sta­ble 100 MV/m gra­di­ent op­er­a­tion of a num­ber of CLIC pro­to­type struc­tures. These struc­tures were fab­ri­cat­ed ba­si­cal­ly using the tech­nol­o­gy de­vel­oped from 1994 to 2004 for the GLC/NLC lin­ear col­lid­er ini­tia­tive. One goal has been to re­fine the es­sen­tial pa­ram­e­ters and fab­ri­ca­tion pro­ce­dures need­ed to re­al­ize such high gra­di­ent rou­tine­ly. An­oth­er goal has been to de­vel­op struc­tures with stronger dipole mode damp­ing than those for GLC/NLC. The lat­ter re­quires that sur­face tem­per­a­ture rise dur­ing the puls­es be high­er, which may in­crease the break­down rate. Struc­tures with heavy damp­ing will be test­ed in late 2009/early 2010, and this paper will pre­sent these re­sults to­geth­er with some of the ear­li­er re­sults from non-damped struc­tures and struc­tures built with a quad­rant ge­om­e­try.

• S. Kazakov, T. Higo, S. Matsumoto
  KEK, Ibaraki

A waveg­uide vac­u­um valve for WR90 waveg­uide was de­signed, fab­ri­cat­ed and test­ed. The valve con­sists of a mod­i­fied com­mer­cial gate valve sand­witched with smooth ta­pers. The TE10 trav­el­ing wave in WR90 waveg­uide is "trans­mod­ed" into TE¹¹⁺TM11 mode in the taper, going through the gate valve and is ta­pered back to the nor­mal mode in WR90. The test has been suc­cess­ful­ly done. The valve sta­bly trasmit­ted 40MW peak power with 500ns pulse width and this is lim­it­ed by avail­able RF power source.

• S. Matsumoto, M. Akemoto, T. Higo, H. Honma, K. Kakihara, T. Kamitani, H. Nakajima, K. Nakao, Y. Ogawa, Y. Yano, K. Yokoyama, M. Yoshida
  KEK, Ibaraki

In order to im­prove the cap­ture ef­fi­cien­cy of the positron pro­duced at the tar­get in pre­sent KEKB In­jec­tor linac, a new pro­ject has just start­ed to uti­lize L-band (1298MHz) RF. The pre­sent S-band (2856MHz) cap­ture cav­i­ties and suc­ces­sive three RF units are to be re­placed by those of L-band. The spec­i­fi­ca­tions of the L-Band sys­tem should ful­fill the de­mands of a positron damp­ing ring down­stream which is also to be under study for super KEKB pro­ject. Be­sides the whole de­sign work of the sys­tem, our pre­sent on­go­ing work is rather con­cen­trat­ed on es­tab­lish­ing L-Band RF source and ac­cel­er­at­ing struc­tures.

• J.W. Wang, J.R. Lewandowski, J.W. Van Pelt, C. Yoneda
  SLAC, Menlo Park, California
• B.A. Gudkov, G. Riddone
  CERN, Geneva
• T. Higo, T. Takatomi
  KEK, Ibaraki

A CERN-SLAC-KEK col­lab­o­ra­tion on high gra­di­ent X-band struc­ture re­search has been es­tab­lished in order to demon­strate the fea­si­bil­i­ty of the CLIC base­line de­sign for the main linac sta­bly op­er­at­ing at more than 100 MV/m load­ed ac­cel­er­at­ing gra­di­ent. Sev­er­al pro­to­type CLIC struc­tures were suc­cess­ful­ly fab­ri­cat­ed and high power test­ed. They op­er­at­ed at 105 MV/m with a break­down rate that meets the CLIC lin­ear col­lid­er spec­i­fi­ca­tions of < 5·10^-7/pulse/m. This paper sum­ma­rizes the fab­ri­ca­tion tech­nolo­gies in­clud­ing the me­chan­i­cal de­sign, pre­ci­sion ma­chin­ing, chem­i­cal clean­ing, dif­fu­sion bond­ing as well as vac­u­um bak­ing and all re­lat­ed as­sem­bly tech­nolo­gies. Also, the tol­er­ances con­trol, tun­ing and RF char­ac­ter­i­za­tion will be dis­cussed.

• T. Sugimura, M. Akemoto, D.A. Arakawa, A. Enomoto, S. Fukuda, K. Furukawa, T. Higo, H. Honma, M. Ikeda, E. Kadokura, K. Kakihara, T. Kamitani, H. Katagiri, M. Kurashina, S. Matsumoto, T. Matsumoto, H. Matsushita, S. Michizono, K. Mikawa, T. Miura, H. Nakajima, K. Nakao, Y. Ogawa, S. Ohsawa, M. Satoh, T. Shidara, A. Shirakawa, T. Suwada, T. Takenaka, Y. Yano, K. Yokoyama, M. Yoshida
  KEK, Ibaraki

The next gen­er­a­tion B-fac­to­ry 'Su­perKEKB' pro­ject whose tar­get lu­mi­nos­i­ty is 8 ×10³⁵ cm^-2s^-1 is under con­sid­er­a­tion. A 'nano-beam scheme' is in­tro­duced to the Su­perKEKB. In the scheme, an elec­tron beam (En­er­gy = 7 GeV, Charge = 3-4 nC/bunch, Ver­ti­cal emit­tance =2.8 x 10^-5 m) and a positron beam (En­er­gy = 4 GeV, Charge = 4 nC/bunch, Ver­ti­cal emit­tance = 1.6 x 10^-5 m), are re­quired at the end of in­jec­tor linac. They are quite chal­leng­ing tar­gets for the pre­sent linac. In order to meet the re­quire­ments, we will in­tro­duce some new com­po­nents to the linac. They are a pho­to-cath­ode RF gun for an elec­tron beam, a positron cap­ture sec­tion using new L-band cav­i­ties, a newly de­signed positron-gen­er­a­tion tar­get sys­tem and a damp­ing ring for a positron beam. This pre­sen­ta­tion shows a strat­e­gy of our in­jec­tor up­grade.