• M. Eshraqi, M. Brandin, I. Bustinduy, C.J. Carlile, H. Hahn, M. Lindroos, C. Oyon, S. Peggs, A. Ponton, K. Rathsman
  ESS, Lund
• R. Calaga, T. Satogata
  BNL, Upton, Long Island, New York
• A. Jansson
  Fermilab, Batavia

A three year de­sign up­date for the Eu­ro­pean Spal­la­tion Source (ESS) linac is just start­ing and a full re­view of this work will be pre­sent­ed. The ac­cel­er­a­tion in the medi­um en­er­gy part of the LINAC using the spoke cav­i­ties have been op­ti­mized and the rest of the ma­chine has been re­designed to in­cor­po­rate this op­ti­miza­tion. The ESS LINAC will de­liv­er an av­er­age power of 5~MW to the tar­get in the nom­i­nal de­sign and the pos­si­bil­i­ty to up­grade to 7.5~MW has been in­clud­ed in all the de­sign steps.

Acknowledgments to all the people in the ESS LINAC Reference Group.

• M. Chung, A. Jansson, A. Moretti, A.V. Tollestrup, K. Yonehara
  Fermilab, Batavia
• A. Kurup
  Imperial College of Science and Technology, Department of Physics, London

To demon­strate the fea­si­bil­i­ty of a high pres­sure RF cav­i­ty for use in the cool­ing chan­nel of a muon col­lid­er, an ex­per­i­men­tal setup that uti­lizes 400-MeV Fer­mi­lab linac pro­ton beam has been de­vel­oped. In this paper, we de­scribe the beam di­ag­nos­tics and the col­li­ma­tor sys­tem for the ex­per­i­ment, and re­port the ini­tial re­sults of the beam com­mis­sion­ing. The tran­sient re­sponse of the cav­i­ty to the beam is mea­sured by the elec­tric and mag­net­ic pick­up probes, and the beam-gas in­ter­ac­tion is mon­i­tored by the op­ti­cal di­ag­nos­tic sys­tem com­posed of a spec­trom­e­ter and two PMTs.

• M. Chung, A. Jansson, A.V. Tollestrup, K. Yonehara
  Fermilab, Batavia
• Z. Insepov
  ANL, Argonne

Ion­iza­tion cool­ing is a crit­i­cal build­ing block for the re­al­iza­tion of a muon col­lid­er. To sup­press break­down in the pres­ence of the ex­ter­nal mag­net­ic field, an idea of using an RF cav­i­ty filled with high pres­sure hy­dro­gen gas is being con­sid­ered for the cool­ing chan­nel de­sign. In the high pres­sure RF cav­i­ty, ion­iza­tion en­er­gy loss and lon­gi­tu­di­nal mo­men­tum re­cov­ery can be achieved si­mul­ta­ne­ous­ly. One pos­si­ble prob­lem ex­pect­ed in the high pres­sure RF cav­i­ty is, how­ev­er, the dis­si­pa­tion of sig­nif­i­cant RF power through the elec­trons ac­cu­mu­lat­ed in­side the cav­i­ty. The elec­trons are gen­er­at­ed from the beam-in­duced ion­iza­tion of the high pres­sure gas. To char­ac­ter­ize this detri­men­tal load­ing ef­fect, we de­vel­op a sim­pli­fied model that re­lates the elec­tron den­si­ty evo­lu­tion and the ob­served pick­up volt­age sig­nal in the cav­i­ty, with con­sid­er­a­tion of sev­er­al key molec­u­lar pro­cess­es such as the for­ma­tion of the poly­atom­ic molecules and ions, ex­ci­ta­tion, re­com­bi­na­tion and elec­tron at­tach­ment. This model is ex­pect­ed to be com­pared with the ac­tu­al beam test of the cav­i­ty in the Mu­Cool Test Area (MTA) of Fer­mi­lab.

• 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.

• P. Snopok, L. Coney
  UCR, Riverside, California
• A. Jansson
  Fermilab, Batavia
• C.T. Rogers
  STFC/RAL/ASTeC, Chilton, Didcot, Oxon

In the Muon Ion­iza­tion Cool­ing Ex­per­i­ment (MICE), muons are cooled by ion­iza­tion cool­ing. Muons are passed through ma­te­ri­al, re­duc­ing the total mo­men­tum of the beam. This re­sults in a de­crease in trans­verse emit­tance and a slight in­crease in lon­gi­tu­di­nal emit­tance, but over­all re­duc­tion of 6D beam emit­tance. In emit­tance ex­change, a dis­per­sive beam is passed through wedge-shaped ab­sorbers. Muons with high­er en­er­gy pass through more ma­te­ri­al, re­sult­ing in a re­duc­tion in lon­gi­tu­di­nal and trans­verse emit­tance. Emit­tance ex­change is a vital tech­nol­o­gy for a Muon Col­lid­er and may be of use for a Neu­tri­no Fac­to­ry. Two ways to demon­strate emit­tance ex­change in the straight solenoidal lat­tice of MICE are dis­cussed. One is to let a muon beam pass through a wedge shaped ab­sorber; the input beam dis­tri­bu­tion must be care­ful­ly se­lect­ed to ac­com­mo­date chro­mat­ic aber­ra­tions in the solenoid lat­tice. An­oth­er ap­proach is to use the input beam for MICE with­out beam se­lec­tion. In this case no poly­no­mi­al weight­ing is in­volved; how­ev­er, a more so­phis­ti­cat­ed shape of the ab­sorber is re­quired to re­duce lon­gi­tu­di­nal emit­tance.

• A.D. Bross, M. Chung, A. Jansson, A. Moretti, K. Yonehara
  Fermilab, Batavia
• D. Huang, Y. Torun
  IIT, Chicago, Illinois
• D. Li
  LBNL, Berkeley, California
• J. Norem
  ANL, Argonne
• R. B. Palmer, D. Stratakis
  BNL, Upton, Long Island, New York
• R.A. Rimmer
  JLAB, Newport News, Virginia

TThe Mu­Cool RF Pro­gram fo­cus­es on the study of nor­mal con­duct­ing RF struc­tures op­er­at­ing in high mag­net­ic field for ap­pli­ca­tions in muon ion­iza­tion cool­ing for Neu­tri­no Fac­to­ries and Muon Col­lid­ers. This paper will give an overview of the pro­gram, which will in­clude a de­scrip­tion of the test fa­cil­i­ty and its ca­pa­bil­i­ties, the cur­rent test pro­gram, and the sta­tus of a cav­i­ty that can be ro­tat­ed in the mag­net­ic field which al­lows for a more de­tailed study of the max­i­mum sta­ble op­er­at­ing gra­di­ent vs. mag­net­ic field strength and angle.

• Y. Torun, D. Huang
  IIT, Chicago, Illinois
• A.D. Bross, M. Chung, A. Jansson, A. Kurup, J.R. Misek, A. Moretti
  Fermilab, Batavia
• J. Norem
  ANL, Argonne

Muon cool­ing re­quires high-gra­di­ent nor­mal con­duct­ing cav­i­ties op­er­at­ing in mul­ti-Tes­la mag­net­ic fields for muon beam fo­cus­ing in an ion­iza­tion cool­ing chan­nel. Re­cent ex­pe­ri­ence with an 805-MHz pill­box cav­i­ty at the Fer­mi­lab Mu­Cool Test Area has shown sig­nif­i­cant drop in ac­cel­er­at­ing field per­for­mance for the case of par­al­lel elec­tric and mag­net­ic fields. It has been sug­gest­ed that hav­ing the mag­net­ic field per­pen­dic­u­lar to the elec­tric field should pro­vide mag­net­ic in­su­la­tion and sup­press break­down. An 805-MHz Cu rect­an­gu­lar box cav­i­ty was built for test­ing with the fields per­pen­dic­u­lar. It was mount­ed on an ad­justable sup­port to vary the angle be­tween the rf elec­tric and ex­ter­nal mag­net­ic field. We re­port on de­sign and op­er­a­tion of the rect­an­gu­lar box cav­i­ty.