Gifford McMahon Machine Used for Precooling of Two Superconducting Cavities at ESRF

A cryo‐module housing two superconducting 352 MHz‐cavities has been developed within the framework of the SOLEIL project design phase. In 2002, the prototype was installed on the ESRF storage ring and tested with beam in the accelerating regime at 4.5 K with the cavities cooled by liquid helium from Dewars. Four such 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 a passive regime, where they remained transparent to the beam. Less than 100 W of heat generated by the beam had then to be evacuated by a helium gas flow. The week of shut down before each test period was used to pre‐cool the module by means of helium gas at a flow rate of 12.5 Nm3/h, the helium being cooled by a Gifford McMahon machine AL300 built by Cryomech (USA). The aim of this poster is to show the special design of the cold head and the way of cooling down the system.