Traveling Wave RF Systems for Helical Cooling Channels

The great ad­van­tage of the he­li­cal ion­iza­tion cool­ing chan­nel (HCC) is its com­pact struc­ture that en­ables the fast cool­ing of muon beam 6-di­men­sion­al phase space. This com­pact as­pect re­quires a high av­er­age RF gra­di­ent, with few places that do not have cav­i­ties. Also, the muon beam is dif­fuse and re­quires an RF sys­tem with large trans­verse and lon­gi­tu­di­nal ac­cep­tance. A trav­el­ing wave sys­tem can ad­dress these re­quire­ments. First, the num­ber of RF power cou­pling ports can be sig­nif­i­cant­ly re­duced com­pared with our pre­vi­ous pill­box con­cept. Sec­ond­ly, by adding a nose on the cell iris, the pres­ence of thin metal foils tra­versed by the muons can pos­si­bly be avoid­ed. We show sim­u­la­tions of the cool­ing per­for­mance of a trav­el­ing wave RF sys­tem in a HCC, in­clud­ing cav­i­ty ge­ome­tries with in­ter-cell RF power cou­plers need­ed for power prop­a­ga­tion.