A New Cooling System for Cryocooled Permanent Magnet Undulators at Diamond Light Source

In this paper we report about the first test results of a new system to cool the magnet girders of a Cryogenic Permanent Magnet Undulator (CPMU) using a liquid nitrogen thermosiphon to drive the circulation. This has the advantage of absorbing large amounts of heat with very small temperature gradients. By choosing the right pipe diameters and using a combination of variable impedance and heaters the thermosiphon can be set up in such a way that the nitrogen is boiling inside the cooling channels thereby reducing the temperature variation along the girder and minimising the temperature rise for heat loads up to several hundreds of watts.