Successful beam test of the HOM free superconducting SOLEIL cavity prototype at the ESRF

A cryo-module housing two strongly HOM damped 352 MHz superconducting (SC) cavity cells has been developed within the framework of the SOLEIL project design phase. In 2002, the prototype was installed in the ESRF storage ring and tested with beam in the accelerating regime with the cavities cooled down to 4.5 K by means of liquid helium from Dewars. Four series of tests have been carried out at the end of scheduled shutdowns. In order not to disturb the ESRF machine performance during the user mode of operation, the cavities were maintained detuned at room temperature. In this passive regime, they remained transparent to the beam with less than 100 W of heat deposited by the beam and evacuated by a warm helium gas flow. Up to 170 mA of beam could be accelerated with a peak RF voltage of 3 MV and a power of 360 kW from the SC module. This corresponds to the performance required for the first SOLEIL operation phase. The concept of effective HOM damping was validated up to the maximum ESRF intensity of 200 mA. A few week points already identified at previous CERN tests were confirmed: high static cryogenic losses, poor cooling of one HOM coupler and too high fundamental power through the dipolar HOM couplers.