We have developed and installed two accelerator-based cold neutron sources within a electron linac at Hokkaido University and a proton synchrotoron at National Laboratory for High Energy Physics. Solid methane at 20K was adopted as the cold moderator. The methane condensing heat exchangers attached directly to the moderator chambers were cooled by helium gas, which was kept cooled in refrigerators and circulated by ventilation fans. Two cold neutron sources have operated smoothly and safely for the past several years. In this paper we describe some of the results obtained in the preliminary experiments by using a modest capacity refrigerator, the design philosophy of the cooling system for the pulsed cold neutron sources, and outline of two facilities.
An outline of the Superconducting Super Collider (SSC) project, a 20TeV on 20TeV proton-proton collider, is given. The SSC will have immense potential for major advances in understanding the nature of matter. Background information and specifications for the three different types of superconducting magnet with emphasizing various magnetic fields (low field option 3T, medium field option 5T, high field option 6.5T) are provided. Also discussed are specific R & D needs of the SSC project.
Heat transfer from horizontal copper surface to liquid helium at near the lambda line is measured in the range of saturated pressure to 8.0kgf/cm2. The heat transfer surface is 2.0cm in diameter and heated electrically. In nucleate boiling of He I heat transfer at near the lambda point the temperature of the heat transfer surface increases rapidly in step heat input and then decreases very slowly toward steady state. In natural convection regime, large and slow fluctuations in surface temperature observed. In pressurized He II, below the critical pressure, heat transfer data obtained at close lambda temperature show the behavior of nucleate boiling of subcooled He I. Above the critical pressure He II heat transfer data near lambda temperature show transition to boiling curve different from that of supercritical He I heat transfer.
For the purpose of clarifying the fracture toughness and microfracture mechanism of fiber reinforced plastics composites at cryogenic temperature 4K, fracture toughness tests were performed for a short glass fiber reinforced polyester composite. Acoustic emission signals were also detected during the fracture toughness tests to obtain a reasonable explanation of the microfracture mechanism. The results are summarized, as follows: (1) The maximum load on the load-displacement curve at 4K increases by about three times that at room temperature 297K. (2) The AE activity for the specimen at 4K is extremely higher than that at 297K. (3) The fracture toughness KAE, which is defined as the critical stress intensity factor corresponding to the abrupt increase of AE energy, becomes larger with decreasing temperature below room temperature. (4) The fracture toughness obtained by the 5% offset procedure of ASTM standard does not agree with the fracture toughness KAE. (5) The AE signals were discriminated into two types by the spectrum analysis and the microfracture mechanism was discussed.
A multifilamentary NbTi composite conductor, which contains about 10 thousands sub-micron diameter filaments, has been manufactured in long lengths. Fine filament size of 0.52μm, a tight twist pitch of 1.13mm for the wire diameter of 0.11mm and Cu-CuNi mixed matrix resulted in strongly reduced a. c. losses; the hysteresis loss and the coupling loss were observed to be 73kW/m3 and 56kW/m3 respectively in the alternating magnetic field of 50Hz with an amplitude of 1.5T. A triplex conductor was constructed by cabling three strands at a twisting pitch of 2.4mm. Several small coils wound from this cable were operated at 50Hz. One of the coils generated a maximum field of 1.52T at the operation current which was very close to the static critical current. Preliminary design studies have shown that, if this conductor is used in superconducting armature windings of rotating machines, considerable economical benefits are obtained compared with conventional armatures. These results will open new prospects for industrial applications of superconductivity in high ramp rate pulsed magnets and power frequency devices.