The TESLA Cryogenic Distribution System

The construction of the 33 km long 500 GeV centre-of-mass energy (upgradeable to 800 GeV) superconductinglinear collider TESLA at DESY with an integrated X-ray FEL facility of 0.1 nm wavelength has been proposed by an international collaboration. The collider will consist of more than 21000 superconducting 9-cell 1.3 GHz RF cavities assembled in about 1800 cryomodules containing also a superconducting magnet package with a quadrupole and dipole steering coils. The paper describes the cryogenic distribution system necessary for cooling to 2 K, mainly consisting of twelve 2.5 km long cooling chains (cryogenic units) of cryomodules, and gives information on the heat load budget, on operating modes as well as on the energy upgrade philosophy