• B.D.S. Hall, G. Burt, C. Lingwood
  Cockcroft Institute, Lancaster University, Lancaster
• R.A. Rimmer, H. Wang
  JLAB, Newport News, Virginia

The planned lu­mi­nos­i­ty up­grade to LHC is like­ly to ne­ces­si­tate a large cross­ing angle and a local crab cross­ing scheme. For this scheme crab cav­i­ties align bunch­es prior to col­li­sion. The scheme re­quires at least four such cav­i­ties, a pair on each beam line ei­ther side of the in­ter­ac­tion point (IP). Up­stream cav­i­ties ini­ti­ate ro­ta­tion and down­stream cav­i­ties can­cel ro­ta­tion. Can­cel­la­tion is usu­al­ly done at a lo­ca­tion where the op­tics has re-aligned the bunch. The beam line sep­a­ra­tion near the IP ne­ces­si­tates a more com­pact de­sign than is pos­si­ble with el­lip­ti­cal cav­i­ties such as those used at KEK. The re­duc­tion in size must be achieved with­out an in­crease in the op­er­a­tional fre­quen­cy to main­tain com­pat­i­bil­i­ty with the long bunch length of the LHC. This paper pro­pos­es a suit­able su­per­con­duct­ing vari­ant of a four rod coax­i­al de­flect­ing cav­i­ty (to be phased as a crab cav­i­ty), and pre­sents an­a­lyt­i­cal mod­els and sim­u­la­tions of suit­able de­signs.

• R.A. Rimmer, W.A. Clemens, J. Henry, P. Kneisel, K. Macha, F. Marhauser, L. Turlington, H. Wang
  JLAB, Newport News, Virginia

JLab has de­signed and fab­ri­cat­ed sev­er­al pro­to­type SRF cav­i­ties with cell shapes op­ti­mized for high cur­rent beams and with strong damp­ing of un­want­ed high­er order modes. We re­port on the lat­est test re­sults of these cav­i­ties and on de­vel­op­ments of con­cepts for new vari­ants op­ti­mized for par­tic­u­lar ap­pli­ca­tions such as light sources and high-pow­er pro­ton ac­cel­er­a­tors, in­clud­ing betas less than one. We also re­port on progress to­wards a first beam test of this de­sign in the re­cir­cu­la­tion loop of the JLab ERL based FEL. With grow­ing in­ter­est world­wide in ap­pli­ca­tions of SRF for high-av­er­age power elec­tron and hadron ma­chines, a prac­ti­cal test of these con­cepts is high­ly de­sir­able. We plan to pack­age two pro­to­type cav­i­ties in a de-mount­able cry­omod­ule for tem­po­rary in­stal­la­tion into the JLab FEL for test­ing with RF and beam. This will allow ver­i­fi­ca­tion of all crit­i­cal de­sign and op­er­a­tional pa­ram­e­ters paving the way to a full-scale pro­to­type cry­omod­ule.

• H. Wang, G. Cheng, G. Ciovati, J. Henry, P. Kneisel, R.A. Rimmer, G. Slack, L. Turlington
  JLAB, Newport News, Virginia
• R. Nassiri, G.J. Waldschmidt
  ANL, Argonne

A squashed, el­lip­ti­cal su­per­cond­con­duct­ing (SC) cav­i­ty with waveg­uide dampers on the beam pipes has cur­rent­ly been cho­sen as the base­line de­sign [1] for the Short Pulse X-ray (SPX) pro­ject at the Ad­vanced Pho­ton Source (APS). An al­ter­nate cav­i­ty de­sign, with a waveg­uide damper lo­cat­ed di­rect­ly on the cav­i­ty cell for im­proved damp­ing char­ac­ter­is­tics, has also been de­signed and cold-test­ed with promis­ing re­sults. In ei­ther case, eight cav­i­ties would be op­er­at­ed CW in a sin­gle cry­omod­ule at 2K to pro­duce an elec­tron bunch chirp of 4MV at a fre­quen­cy of 2.815 GHz. De­tailed anal­y­sis of mul­ti­pactor­ing (MP), lorentz force de­tun­ing (LFD), and the ther­mal prop­er­ties of the base­line de­sign has led to an en­gi­neer­ing spec­i­fi­ca­tion of the basic pa­ram­e­ters of the cry­omod­ule.

• H. Wang, G.K. Davis, R.A. Rimmer
  JLAB, Newport News, Virginia
• G. Burt, R.G. Carter, A.C. Dexter, M.I. Tahir
  Cockcroft Institute, Lancaster University, Lancaster

The use of an in­jec­tion locked CW mag­netron to drive a 2.45 GHz su­per­con­duct­ing RF cav­i­ty has been suc­cess­ful­ly demon­strat­ed. With a lock­ing power less than -27 dB with re­spect to the out­put and with a phase con­trol sys­tem act­ing on the lock­ing sig­nal, cav­i­ty phase was ac­cu­rate­ly con­trolled for hours at a time with­out loss of lock whilst sup­press­ing mi­cro­phon­ics. The phase con­trol ac­cu­ra­cy achieved was 0.8o r.m.s. The main con­tribut­ing dis­tur­bance lim­it­ing ul­ti­mate phase con­trol was power sup­ply rip­ple from the low spec­i­fi­ca­tion switch mode power sup­ply used for the ex­per­i­ment.

• K. Yonehara, M. Chung, A. Jansson, A. Moretti, M. Popovic, A.V. Tollestrup
  Fermilab, Batavia
• M. Alsharo'a, R.P. Johnson, M. Notani
  Muons, Inc, Batavia
• D. Huang
  IIT, Chicago, Illinois
• Z. Insepov
  ANL, Argonne
• T. Oka, H. Wang
  University of Chicago, Chicago, Illinois
• D. Rose
  Voss Scientific, Albuquerque, New Mexico

A high pres­sur­iz­ing hy­dro­gen gas filled RF cav­i­ty has a great po­ten­tial to apply for muon col­lid­ers. It gen­er­ates high elec­tric field gra­di­ents in strong mag­net­ic fields with var­i­ous con­di­tions. As the re­main­ing demon­stra­tion, it must work under high ra­di­a­tion con­di­tions. A high in­ten­si­ty muon beam will gen­er­ate a beam-in­duced elec­tron swarm via the ion­iza­tion pro­cess in the cav­i­ty. A large amount of RF power will be con­sumed into the swarm. We show the re­cent non-beam test and dis­cuss the elec­tron swarm dy­nam­ics which plays a key role to de­vel­op a high pres­sure RF cav­i­ty.