This paper introduces the Francis Bitter National Magnet Laboratory. It provides a brief history of the Laboratory and a description of its high-field facilities. Also discussed are hybrid magnets and their important requirements as facility magnets. Furthermore, discussion is presented on the critical roles that structure and materials play in determining the strength of resistive inserts for hybrid magnets and on the relationship between power input to the insert and the central field. The paper concludes with a suggestion for the future direction of hybrid magnet based on the use of high-temperature superconducting magnets.
Frictional heat generated during sliding of two surfaces is transferred to their substrates through real contact points. To obtain the distribution of real contact points of a JN1-JN1 contact interface, a thin PET film method, previously developed by the present author, was used. On the basis of this distribution of the real contact points, the temperature inside the JN1, which had the shape of a rectangular prism and was immersed in liquid helium, was calculated by 3-dimensional FEM analysis. Two extreme boundary conditions at the contacting interface were taken into account since it was difficult to determine the reasonable boundary condition. One condition was that the temperature at the contact surface other than the real contact area was kept at a constant value of 4.2K and the other was adiabatic. In the case of the adiabatic boundary condition, the distribution of the real contact area affected the distribution of temperature at depths down to 2mm.
Double-inlet pulse tube refrigerators have a phase shifter, which is located at the hot end of the pulse tube and consists of an orifice valve, a bypass valve, and a reservoir tank. Linearized thermoacoustic theory suggests that the phase shift between pressure and displacement of gas has a strong influence on the performance of the refrigerator. In this report, instantaneous mass flow rates of the gas through the orifice and the bypass valves were measured by hot-wire anemometers to estimate the phase shift. The experimental results indicate that the phase shift can be over 90° in a double-inlet pulse tube refrigerator, while it is below 90° in an orifice pulse tube refrigerator. The experimental results also show that not only the phase shift but also the average mass flow rate at the hot end of the pulse tube must be optimized to reach the minimum temperature. Further, numerical simulation based on linearized thermoacoustic theory was conducted to estimate the effects of the average mass flow rate and the phase shift. The calculated results show that the thermoacoustic theory may be applied to estimate the performance of pulse tube refrigerators.