A Superconducting 352 MHz Prototype Cavity for LEP

It is proposed to upgrade the large electron-positron storage ring LEP to energies above the initial 55 GeV by superconducting accelerating cavities operated at 352 MHz. A new cavity geometry has been developed which will allow to locate the main and higher order mode couplers at the beam tubes of the cavities. Experimental results obtained with monocell cavities fabricated from niobium material of different thermal conductivity and with a 4-cell prototype cavity are discussed.