The refrigeration and cryogenic distribution system for the shortpulse x-ray source

Abstract

This report describes the essential elements of the cryogenic system. The cryogenic distribution system starts at the level of the linac superconducting RF cavities [1] and moves out through the cryogenic piping to the liquid helium refrigeration plant that will be used to cool the RF cavities and the undulator magnets. For this report, the cryogenic distribution system and cryogenic refrigerator includes the following elements: (1) The piping within the linac cryogenic modules will influence the heat transfer through the super-fluid helium from the outer surface of the TESLA niobium cavity and the liquid to gas interface within the horizontal header pipe where the superfluid helium boils. This piping determines the final design of the linac cryogenic module. (2) The acceptable pressure drops determine the supply and return piping dimensions. (3) The helium distribution system is determined by the need to cool down and warm up the various elements in the light source. (4) The size of the cryogenic plant is determined by the heat loads and the probable margin of error on those heat loads. Since the final heat loads are determined by the acceleration gradient in the cavities, a linac with five cryogenic modules will be compared to a linac with only four cryogenic modules. The design assumes that all cryogenic elements in the facility will be cooled using a common cryogenic plant. To minimize vibration effects on the beam lines, this plant is assumed to be located some distance from the synchrotron light beam lines. All of the cryogenic elements in the facility will be attached to the helium refrigeration system through cryogenic transfer lines. The largest single cryogenic load is the main linac, which consists of four or five cryogenic modules depending on the design gradient for the cavities in the linac section. The second largest heat load comes from the cryogenic modules that contain the transverse deflecting RF cavities. The injector linac is the third largest heat load. The seven superconducting undulator magnets in the hard x-ray production section are the smallest heat loads connected to the light source refrigeration plant. The linac and deflecting cavity sections require helium cooling at 1.9 K, 5 K and 40 K. The undulator magnets require two-phase helium cooling at 4.3 to 4.5 K.