The TESLA 500 cryogenic system layout

The superconducting 2 x 250 GeV e+e- linear accelerator TESLA is composed of a series of high frequency resonators (cavities), fabricated of high purity niobium. It has to be operated at a temperature of ca. 2 K. A nominal refrigeration power of about 51 KW at 2 K, 37 KW at 4.5 K and 314 KW at 40/80 K is required. The cooling power has to be distributed over a distance of more than 30 km, Different aspects of the cryogenic system are discussed.