• A.V. Zlobin, E.Z. Barzi, V.S. Kashikhin, M.J. Lamm, V. Lombardo, M.L. Lopes, M. Yu
  Fermilab, Batavia
• G. Flanagan, R.P. Johnson, S.A. Kahn, M. Turenne
  Muons, Inc, Batavia

The He­li­cal Cool­ing Chan­nel (HCC) is a tech­nique pro­posed for six-di­men­sion­al (6D) cool­ing of muon beams. The HCC for muon col­lid­er and some other ap­pli­ca­tions is usu­al­ly di­vid­ed into sev­er­al sec­tions each with pro­gres­sive­ly stronger fields, small­er aper­ture, and short­er helix pe­ri­od to achieve the op­ti­mal muon cool­ing rate. Novel mag­net de­sign con­cepts based on sim­ple coils ar­ranged in a he­li­cal solenoid con­fig­u­ra­tion have been de­vel­oped to pro­vide HCC mag­net sys­tems with the de­sired pa­ram­e­ters. The level of mag­net­ic field in the HCC high-field sec­tions sug­gests using a hy­brid coil struc­ture with High Tem­per­a­ture Su­per­con­duc­tors (HTS) in the in­ner­most coil lay­ers and Nb₃Sn su­per­con­duc­tor in the outer coil lay­ers. The de­vel­op­ment of the con­cepts and en­gi­neer­ing de­signs of hy­brid he­li­cal solenoids based on ad­vanced su­per­con­duc­tor tech­nolo­gies, with spe­cial em­pha­sis on the use of HTS for high fields at low tem­per­a­ture is the key step to­wards a prac­ti­cal HCC. This paper de­scribes the con­cep­tu­al de­signs and pa­ram­e­ters of a short HTS model of a hy­brid he­li­cal solenoid, and dis­cuss­es the struc­tural ma­te­ri­als choic­es, fab­ri­ca­tion tech­niques, and first test re­sults.

• S.A. Kahn, G. Flanagan, R.P. Johnson, M. Turenne
  Muons, Inc, Batavia
• F. Hunte, J. Schwartz
  North Carolina State University, Raleigh, North Carolina

YBCO su­per­con­duc­tors orig­i­nal­ly de­vel­oped for high tem­per­a­ture op­er­a­tion carry sig­nif­i­cant crit­i­cal cur­rent even in the pres­ence of ex­treme­ly high mag­net­ic field when op­er­at­ed at low tem­per­a­ture. The final stage of phase space cool­ing for a muon col­lid­er uses a solenoid mag­net with fields ap­proach­ing 50 T. As part of an R&D ef­fort we pre­sent mea­sure­ments of me­chan­i­cal and elec­trome­chan­i­cal prop­er­ties of the YBCO con­duc­tor. We ex­am­ine the crit­i­cal cur­rent vers­es mag­net field angle at 4.2 K in a mag­net­ic field. Quench prop­er­ties of the con­duc­tor such as min­i­mum quench en­er­gy thresh­old and quench prop­a­ga­tion ve­loc­i­ty will be mea­sured to es­tab­lish safe op­er­a­tional con­duc­tions for the muon cool­ing mag­nets. In this paper we de­scribe a con­cep­tu­al pic­ture for a high field solenoid to be used for muon phase space cool­ing that in­cor­po­rates these low tem­per­a­ture prop­er­ties of YBCO.

• M. Turenne, R.P. Johnson, S.A. Kahn
  Muons, Inc, Batavia
• F. Hunte, J. Schwartz, L. Ye
  North Carolina State University, Raleigh, North Carolina

Mag­net ap­pli­ca­tions for high en­er­gy physics has long been an im­por­tant driv­er for the de­vel­op­ment of su­per­con­duct­ing tech­nol­o­gy. New high tem­per­a­ture su­per­con­duc­tors (HTS), which have very high val­ues of the upper crit­i­cal field Hc2, show promise for mag­nets gen­er­at­ing fields greater than 25 T, such as those re­quired for muon cool­ing [1]. (Rare Earth)Ba2Cu3Oy (REBCO) coat­ed con­duc­tor is an HTS ma­te­ri­al which is well suit­ed to these needs; how­ev­er it re­quires char­ac­ter­i­za­tion in the low tem­per­a­ture (4.2 K), high mag­net­ic field regime. We are propos­ing to mea­sure elec­tro-me­chan­i­cal and mag­net­ic prop­er­ties, in­clud­ing an­gu­lar field de­pen­dence of com­mer­cial­ly avail­able REBCO con­duc­tor. Here we pre­sent re­sults of ini­tial test­ing to char­ac­ter­ize com­mer­cial­ly avail­able REBCO coat­ed con­duc­tors at 77 K, in­clud­ing crit­i­cal cur­rent and quench test­ing to cal­cu­late min­i­mum the quench en­er­gy (MQE) and nor­mal zone prop­a­ga­tion ve­loc­i­ty (NZPV).

• S.A. Kahn, G. Flanagan, R.P. Johnson
  Muons, Inc, Batavia

To achieve the high lu­mi­nos­i­ty re­quired for a muon col­lid­er strong quadrupole mag­nets will be need­ed for the final focus in the in­ter­ac­tion re­gion. These mag­nets will be lo­cat­ed in re­gions with space con­straints im­posed both by the lat­tice and the col­lid­er de­tec­tor. There are sig­nif­i­cant beam re­lat­ed back­grounds from muon de­cays and syn­chrotron ra­di­a­tion which cre­ate un­want­ed par­ti­cles which can de­posit sig­nif­i­cant en­er­gy in the mag­nets of the final focus re­gion of the col­lid­er. This en­er­gy de­po­si­tion re­sults in the heat­ing of the mag­net which can cause it to quench. To mit­i­gate the ef­fects of heat­ing from the en­er­gy de­po­si­tion shield­ing will need to be in­clud­ed with­in the mag­net forc­ing the aper­ture to be larg­er than de­sired and con­se­quent­ly re­duc­ing the gra­di­ent. We pro­pose to use ex­ot­ic high mag­ne­ti­za­tion ma­te­ri­als for pole tips to in­crease the quadrupole gra­di­ent.

• S.A. Kahn, G. Flanagan, R.P. Johnson, M.L. Neubauer
  Muons, Inc, Batavia
• V.S. Kashikhin, M.L. Lopes, K. Yonehara, M. Yu, A.V. Zlobin
  Fermilab, Batavia

A he­li­cal cool­ing chan­nel (HCC) con­sist­ing of a pres­sur­ized gas ab­sorber imbed­ded in a mag­net­ic chan­nel that pro­vides solenoidal, he­li­cal dipole and he­li­cal quadrupole fields has shown con­sid­er­able promise in pro­vid­ing six-di­men­sion­al cool­ing for muon beams. The en­er­gy lost by muons travers­ing the gas ab­sorber needs to be re­placed by in­sert­ing RF cav­i­ties into the HCC lat­tice. Re­plac­ing the sub­stan­tial muon en­er­gy loss­es using RF cav­i­ties with rea­son­able gra­di­ents will re­quire a sig­nif­i­cant frac­tion of the chan­nel length be de­vot­ed to RF. How­ev­er to pro­vide the max­i­mum phase space cool­ing and min­i­mum muon loss­es, the HCC should have a short pe­ri­od and length. In this paper we ex­am­ine an ap­proach where each HCC cell has an RF cav­i­ty imbed­ded in the aper­ture with the mag­net­ic coils are split al­low­ing for half of the cell length to be avail­able for the RF cou­pler and other ser­vices.