Low-beta structures for cw operation

Abstract

Arcing problems and mechanical instabilities may limit the output energy of cw RFQ's even below 2 MeV. Between 2 and 10 MeV, Alvarez type DTL's are not convenient. The proposed structures are derived from slot-coupled, iris loaded, p-mode, 5-cell resonators. But the noses are shaped so that they provide a large enough space at atmospheric pressure to accommodate a magnetic quadrupole, to insure a FODO-type focusing. The beam sees a 3p or a 5p delay-line. Those structures are well suited for 350 MHz, or above, operating frequency, where there is enough space for water pipes to insure a sufficient cooling for cw operation. The focusing quadrupoles are entirely in the air and easily accessible. Fabrication is substantially the same as slot-coupled CCL's and beam dynamics is intermediate between 2p and 4p Alvarez structures.