Superconducting Cavity Beam Test in CESR
The first use of a superconducting accelerating structure in a storage ring is described. Two 5-cell 1500 MHz ''muffin tin'' superconducting niobium cavities (1 m active length) were operated in the Cornell 8 GeV e/sup +/e/sup -/ storage ring, CESR. A 6.1 mA beam was captured and stored at 3.5 GeV using only the superconducting cavity. Up to 12.5 kW was transferred to the beam by the cavity. Single bunch currents up to 12 mA were reached in conjunction with the normal 500 MHz RF. Beam induced higher order mode (HOM) powers of 290 W were carried to room-temperature loads by four couplers and waveguides; no HOM-induced cryogenic dissipation was detectable. Q's of the 76 most prominent resonances were measured. Transverse and longitudinal beam instabilities were studied by mechanically sweeping the tune of the cavities; current thresholds are compared to theory. The cavity exhibited the ability to survive breakdown at high incident power without degradation.
Superconducting Cavities for Synchrotron Use
For two months, as of this writing, a 60 cm length of niobium S-band standing wave accelerator has been installed in the Cornell Electron Synchrotron. The Q0 has remained at its initial value of 1.1 × 109, and the accelerating field at breakdown has remained at 4 MeV/m. The cavity has been used to accelerate the synchrotron beam to 4 GeV by itself and to accelerate the beam to 12 GeV in concert with the normal RF system.
Design Studies for a 1500 MHz Superconducting Accelerator Cavity for use in an e+e− Storage Ring
The cost of a high-energy e+ e− machine can be substantially reduced if superconducting cavities with accelerating gradients of several MV/m can be used1,2). From an RF performance as well as economic point of view, higher operating frequencies are preferred. The upper limit, however, is set by requirements of storage ring operation such as useful aperture, beam bunch length, stored energy, and synchrotron oscillation frequency. Based on these considerations, design studies on a 1500 MHz structure have been carried out with a view towards installing 2m of superconducting cavity in CESR. These studies include measurements on higher-mode properties of the multi-cell structure, tests of devices that provide the coupling necessary for higher-mode power extraction, and damping of instability driving modes, multipactor control techniques on superconducting sections, and tests of 1500 MHz multi-cell superconducting sections.