The design of the RF cavities for Elettra

The authors discuss the optimization of the RF cavities for the Elettra Storage Ring, the synchrotron radiation light facility now under construction in Trieste, Italy. For Elettra´s cavities a very high accelerating voltage is needed due to the tight requirements of the beam quality, together with the very small dimension of the electron bunches: the high bunch charge (0.7 nC) and repetition rate, and the 2.0 GeV of total energy for the storage ring. At the operating frequency of 500 MHz, and at the accelerating voltage of 1 MV per cavity, 3.3 MV/m of accelerating field are needed. A great deal of care was used to define the cavity geometry in order to avoid electron discharges, resonant or not. The optimization results in a multipactor free cavity with a very low nonresonant electron loading current