Design and development of cryogenic system for cryogenic undulator at NSRRC.

A cryogenic system using cryo-coolers is developed for a cryogenic undulator at NSRRC. This system can keep magnet arrays at 50 K for higher magnetic performance in an ultra-high vacuum environment. Separation chambers between the cold head in high vacuum and the magnet array in ultra-high vacuum is necessary. While the magnet arrays are cooled to 50 K, the temperature uniformity on the magnet arrays must be minimized to reduce undulator phase error. For the above reason, cooling locations should be optimized to meet these requirements. To solve the temperature variation of the magnet array due to the beam-induced heat load, 8 heaters on the magnet arrays are used to keep the temperature variation within tolerance. Flexible thermal straps were designed for conducting cool between the cold head and the magnet arrays, in addition to absorbing the length difference of the cryogenic undulator magnet gap. Bellow shafts were specially designed to reduce the conduction of heat transfer between the room temperature of the mechanical frame and the low temperature of the magnet. These heat-load issues and technologies will be discussed in this letter.