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.
It is expected that the normal-zone propagation of high-temperature superconductor (HTS) is slower than that of low-temperature superconductor (LTS) because of its large heat capacity. If the normal-zone propagates too slowly, hot spots will develop, possibly resulting in permanent conductor damage. Accordingly, it is necessary to measure propagation for designing of HTS magnet quantitatively. This paper describes electromagnetical and thermal behaviors during normal transition in Bi-2223/Ag superconducting multifilamentary tapes by conduction cooling. Some experiments were carried using operating temperature, 10-40K, and transport current as parameters in zero magnetic field. Sample tapes are transmitted normally with heater to initiate a quench. The voltage and temperature properties which accord with a normal transition are measured by voltage taps and thermocouples attached to sample tapes, and we also calculated longitudinal and transverse directions normal-zone propagation velocities from the voltage traces. In the case of conduction cooling, we investigate the cooling effect due to the length of the sample tape because its cooling condition is different from the case of using a coolant, for example liquid helium.
In order to improve performances of a very compact dilution refrigerator developed by Ootuka et al., we have modified some parts, which include a condenser and a 3He evacuation tube. Improvements in ultimate temperature and in handling-easiness have been achieved through modification. The ultimate temperatures is 80mK in the continuous mode and 36mK in the one-shot mode.