The Hadron Electron Ring Accelerator (HERA) designed for providing collisions of 30GeV electrons or positrons with 820GeV protons in a ring tunnel of 6.3km 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 4.4K 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 summarised.
Two-dimensional heat transport characterisitics of pressurized He II channels have been experimentally and numerically investigated. The examined channels are 170mm long and 7mm wide with gaps of 5 and 17mm. The channels are kept vertical with both ends open to the bath filled with He II at atmospheric pressure. One of the side walls of the channel is heated uniformly. In the case of the channel with a 17-mm gap it is found from the experiments that although the temperature of He II near the side wall opposite the heated wall remained at He II temperature, He II near the heated wall changes to He I and gas. It is comfirmed from the numerical analysis that the input heat is transported two-dimensionally and a temperature difference is generated in the gap direction when the gap is larger than a certain value.