| Popis: |
Superconducting RF accelerating cavities of different frequencies are presently operating on various accelerators world wide. The large majority of these cavities are made of niobium sheet, by lathe spinning and welding. In one case only, i.e. LEP2 at CERN, the majority of cavities is made of copper, internally coated with a thin layer of sputtered niobium. The main motivation for developing Nb-coated copper cavities mustbe found in the higher stability against quenching, consequent to the higher thermal conductivity of copper at liquid helium temperatures. Additional advantages are higher Q 0 values at low fields, insensitivity to trapped earth magnetic field and lower cost. Beside these advantages, the Nb-coated cavities unfortunately suffer from a faster Q 0 degradation with increasing the accelerating field. The performances of Nb-sheet and Nb-coated cavities are critically compared on the grounds of the large industrial production required by the LEP2 project. |
