• A. Facco, P. Modanese, F. Scarpa
  INFN/LNL, Legnaro (PD)
• Y. Ma
  CIAE, Beijing

The low-beta section of the ALPI linac at Laboratori Nazionali di Legnaro is being upgraded in order to double its energy gain from about 10 MV to 20 MV. This upgrade, performed with a rather limited investment in the background of the standard accelerator activities, is based on the replacement of some rf system components and minor modifications to the cryostats. The cavities, working at 80 MHz, require a 3 dB rf bandwidth of 15 Hz (obtained by means of strong overcoupling) to be locked in the presence of the large Helium pressure fluctuations of ALPI. Their average gradient, although exceeding 6 MV/m at the nominal 7 W power, is presently kept around 3 MV/m during operation, limited by the maximum available rf power in the linac. The ongoing upgrade requires the modification of all low-beta cryomodules to allow new, liquid Nitrogen cooled rf couplers and new, 1 kW amplifiers. A fully equipped prototype cryostat with four, beta=0.047 QWRs has been constructed and tested on line, and operated at 6 MV/m reaching or exceeding all the design goals. The test results will be reported and discussed and the project status will be presented.

• Y. Ma
  CIAE, Beijing
• A. Facco, F. Scarpa
  INFN/LNL, Legnaro (PD)

The low-beta section of the EURISOL driver linac is based on 176 MHz superconducting half-wave resonators (HWR) with beta=0.09 and 0.16. These cavities are an evolution of the 352 MHz ones, previously developed in the same framework, having similar dimensions and components except for their length and rf frequency. They are characterized by a double wall, all niobium structure with light weight, good mechanical stability and a side tuner cooled by thermal conduction. The new 176 MHz Half-wave cavities design includes a removable tuner, which allows to improve tuning range, mechanical stability and accessibility to the cavity interior. A beta=0.13 cavity, which could be suitable for linacs like the SARAF one, was also designed with the same concepts. Design characteristics and expected performance will be presented and discussed.

• W. Hartung, S. Bricker, C. Compton, K. Elliott, M. Hodek, J.P. Holzbauer, M.J. Johnson, O.K. Kester, F. Marti, S.J. Miller, D. Norton, J. Popielarski, L. Popielarski, J. Wlodarczak, R.C. York
  NSCL, East Lansing, Michigan
• A. Facco
  INFN/LNL, Legnaro (PD)
• E.N. Zaplatin
  FZJ, Jülich

Niobium quarter-wave resonators (QWRs) and half-wave resonators (HWRs) are being developed at Michigan State University for two projects: a 3 MeV per nucleon superconducting linac for re-acceleration of exotic ions (ReA3, under construction, requiring 15 resonators), and a 200 MeV per nucleon driver linac for the Facility for Rare Isotope Beams (FRIB, under design, requiring 344 resonators). The QWRs (80.5 MHz, optimum beta = 0.041 and 0.085) are required for both ReA3 and FRIB. Both include stiffening elements and frictional dampers. Nine beta = 0.041 QWRs have been fabricated; seven of them have been Dewar tested successfully with a helium vessel for use in ReA3. Production and testing of ten beta = 0.085 QWRs is in progress. The HWRs (322 MHz, optimum beta = 0.29 and 0.53, required for FRIB) are designed for mechanical stiffness and low peak surface magnetic field. A prototype beta = 0.53 HWR has been fabricated, and a prototype beta = 0.29 HWR is planned. This paper will cover the RF and mechanical requirements, the resonator and vessel design, and Dewar testing of production resonators.