• V.P. Yakovlev, T.N. Khabiboulline, N. Solyak, A. Vostrikov
  Fermilab, Batavia
• A. Saini
  University of Delhi, Delhi

Re­sults of anal­y­sis are pre­sent­ed for the lon­gi­tu­di­nal and trans­verse ef­fects of High-Or­der Mode (HOM) ex­ci­ta­tion in the ac­cel­er­a­tion RF sys­tem of the CW pro­ton linac of the Pro­ject X fa­cil­i­ty. Ne­ces­si­ty of HOM dampers in the SC cav­i­ties of the linac is dis­cussed.

• I.R.R. Shinton, R.M. Jones, N. Juntong
  UMAN, Manchester
• N. Baboi
  DESY, Hamburg
• N. Eddy, T.N. Khabiboulline
  Fermilab, Batavia
• T. Flisgen, H.-W. Glock, U. van Rienen
  Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock

We anal­yse the high­er order modes in the 3.9GHz bunch shap­ing cav­i­ties re­cent­ly in­stalled in the XFEL/FLASH fa­cil­i­ty at DESY. We re­port on re­cent ex­per­i­men­tal re­sults on the fre­quen­cy spec­trum, both beam and probe based. These are com­pared to those pre­dict­ed by fi­nite el­e­ment com­put­er codes, glob­alised scat­ter­ing ma­trix cal­cu­la­tions and a two-band cir­cuit model. This study is fo­cused on the dipole com­po­nent of the multi­band ex­pan­sion of the wake­field.

• I.G. Gonin, M.S. Champion, T.N. Khabiboulline, A. Lunin, N. Perunov, N. Solyak, V.P. Yakovlev
  Fermilab, Batavia

In the low-en­er­gy part of the Pro­ject X H-linac there fam­i­lies of 325 MHz SC sin­gle spoke cav­i­ties will be used, hav­ing beta = 0.11, 0.22 and 0.4. Two ver­sions of the beta = 0.11 cav­i­ty were con­sid­ered: low-be­ta sin­gle-spoke cav­i­ty and half-wave cav­i­ty. Re­sults of de­tailed op­ti­miza­tion of both ver­sions are pre­sent­ed. Sin­gle spoke cav­i­ty was se­lect­ed for the linac be­cause of high­er r/Q. Re­sults of the beam dy­nam­ics op­ti­miza­tion for ini­tial stage of the linac with beta=0.11 sin­gle spoke cav­i­ty are pre­sent­ed as well.

• P.V. Avrakhov, A. Kanareykin
  Euclid TechLabs, LLC, Solon, Ohio
• M. Ge, I.G. Gonin, T.N. Khabiboulline, J.P. Ozelis, A.M. Rowe, N. Solyak, G. Wu, V.P. Yakovlev
  Fermilab, Batavia
• J. Rathke
  AES, Medford, NY

Use of a su­per­con­duct­ing trav­el­ling wave ac­cel­er­at­ing (STWA) struc­ture with a small phase ad­vance per cell rather than a stand­ing wave struc­ture may pro­vide a sig­nif­i­cant in­crease in the ac­cel­er­at­ing gra­di­ent in the ILC linac. For the same sur­face elec­tric and mag­net­ic fields the STWA achieves an ac­cel­er­at­ing gra­di­ent 1.2 larg­er than TES­LA-like stand­ing wave cav­i­ties. In ad­di­tion, the STWA al­lows longer ac­cel­er­a­tion cav­i­ties, re­duc­ing the num­ber of gaps be­tween them. How­ev­er, the STWA struc­ture re­quires a SC feed­back waveg­uide to re­turn the few hun­dreds of MW of cir­cu­lat­ing RF power from the struc­ture out­put to the struc­ture input. A test sin­gle-cell cav­i­ty with feed­back was de­signed and man­u­fac­tured to demon­strate the pos­si­bil­i­ty of a prop­er pro­cess­ing to achieve a high ac­cel­er­at­ing gra­di­ent. The first re­sults of high-gra­di­ent tests of a pro­to­type 1.3 GHz sin­gle-cell cav­i­ty with feed­back waveg­uide will be pre­sent­ed.

• E. Vogel, C. Albrecht, N. Baboi, C. Behrens, T. Delfs, J. Eschke, C. Gerth, M.G. Hoffmann, M. Hoffmann, M. Hüning, R. Jonas, J. Kahl, D. Kostin, G. Kreps, F. Ludwig, W. Maschmann, C. Mueller, P. Nommensen, J. Rothenburg, H. Schlarb, Ch. Schmidt, J.K. Sekutowicz
  DESY, Hamburg
• H.T. Edwards, E.R. Harms, A. Hocker, T.N. Khabiboulline
  Fermilab, Batavia
• M. Kuhn
  Uni HH, Hamburg

Ultra short bunch­es with high peak cur­rent are re­quired for ef­fi­cient cre­ation of high bril­liance co­her­ent light at the free elec­tron laser FLASH. They are ob­tained by a two stage trans­verse mag­net­ic chi­cane bunch com­pres­sion scheme based on ac­cel­er­a­tion of the beam off the rf field crest. The de­vi­a­tion of the rf field's sine shape from a straight line leads to long bunch tails and re­duces the peak cur­rent. This ef­fect will be elim­i­nat­ed by adding the Fer­mi­lab-built third har­mon­ic su­per­con­duct­ing ac­cel­er­at­ing mod­ule op­er­at­ing at 3.9 GHz to lin­earize the rf field. The third har­mon­ic mod­ule also al­lows for the cre­ation of uni­form in­ten­si­ty bunch­es of ad­justable length that is need­ed for seed­ed op­er­a­tion. This paper sum­ma­rizes the re­sults from the first com­plete rf sys­tem test at the cry­mod­ule test bench at DESY and the first ex­pe­ri­ence gained op­er­at­ing the sys­tem with beam in FLASH.