Superconducting magnet and cryogenic system of HERA

The Hadron Electron Ring Accelerator (HERA) designed for providing collisions of 30 GeV electrons or positrons with 820 GeV protons in a ring tunnel of 6.3 km circumference is operating at DESY, Hamburg, Germany, since 1991. The proton ring consists of 422 superconducting bending magnets (dipoles), 224 focusing magnets (quadrupoles) and a large number of superconducting correction magnets. For operation these magnets are cooled to 4.4 K by means of a large helium refrigeration plant. The superconducting magnets as well as the cryogenic supply and distribution systems are described and the experience of operation during the last years is summarized. (author)