In the past few years, most DNA constructions have been desided through the project of GENOMICS or civilian companies. But these constructions were only “Drawings for protains.” To develop medical science or to new medicines, the actual construction of all protains must be cleared. High-magnetic field NMR, Nuclear Magnetic Resonance, is the most effective way to analize these protains. Along with the “TROSY” method, a magnetic field required to achieve 25.85T (1.1GHz) to clear all protain constructions. Depending on these requiments, recent development of the magnet forword to achieve heiher magnetic field. On the other hand, critical current: Ic of superconductiving wire almost aproechies its critical value, which depends on material property. The only way to have a heigh magnetic field is to decrease its operating temperature. This paper shows the recent development of cooling techniques below 4.2K, using superfluid helium, including the subcooled helium method, on NMR cryostat.
The LHC project is in progress at CERN. The LHC accelerator, whose beam energy is 7TeV, consists of more than 2, 000main superconducting magnets. Almost all the magnets are to be operated at 1.9K pressurized He II cooling because of the high magnetic field. The cooling system consists of 8 refrigerator units with a large equivalent capacity of 18kW at 4.5K. Each unit covers to cool the aligned magnets along a distance of 3.3km long. In order to obtain 1.9K pressurized He II with better efficiency, 8 cold compressor units will be installed into the 8 refrigeration systems. The necessary cooling of the magnets is obtained with pipe-shaped heat exchangers embedded in magnet iron yokes. The minimum cooling unit of the magnets is composed with the 6main dipole and 2main quadrupole magnets. The unit length is 106m. This paper will describe the outline of the He II refrigeration system.
This paper reviews the authors' recent works on steady-state heat transfer from heated wires and plates in a pool of saturated and subcooled superfluid helium (He II) for liquid temperatures from 1.8 to 2.1K. The following is described: 1) Critical heat fluxes (CHFs) on wires of various diameter and a theoretical CHF correlation based on the Gorter-Mellink equations that can describe the experimental data. 2) CHFs on flat plates with various widths and lengths and a correlation that can describe the experimental data. 3) CHFs on a flat plate at one side of a rectangular duct with various ratios of cross sectional duct area Ad to the heater surface area Ah, and a correlation that can describe the experimental data. 4) Two dimensional numerical analysis on heat transfer in the duct based on a rigorous two fluid model and comparison with the experimental data.
This paper reviews the authors' recent works on transient heat transfer from heated surfaces produced by stepwise heat inputs in a pool of pressurized superfluid helium (He II) for liquid temperatures from 1.8 to 2.1K. The following is described: (1) Typical behavior of transient heat transfer produced by a stepwise heat input; existence of quasi-steady state with a certain lifetime. (2) Lifetimes of quasi-steady states produced by stepwise heat inputs to a flat plate with various width and length and a correlation that can describe the experimental data. (3) Comparison of the lifetimes on flat plates with those on cylinders. (4) The lifetimes on a flat plate at one side of a rectangular duct with various ratios of cross sectional duct area Ad to the heater surface area Ah, and a correlation that can describe the experimental data. (5) The lifetimes on a flat plate at one side of a rectangular duct with an orifice. (6) Two dimensional numerical analysis on heat transfer in the duct based on a rigorous two fluid model and comparison with the experimental data.
A grant-in-aid project on the database development for He II-cooled superconducting magnet system design has been going on as a 3-year project. Many big projects on He II cooled superconducting magnets and cavities have been planned and are under construction around the world. He II systems consist of many specific technologies such as helium heat transfer coefficients under pressurized and saturated superfluid helium conditions, cooling characteristics in micro channels, Kapitza resistance between the surface of heat exchanger, helium pumping techniques, in situ measurement of temperature, pressure under high magnetic fields, and so on. The four organizations including university and national institutes started their collaborative research on this project to develop a convenient and useful database system. Two activities are going on: The first is to pick up the related papers already published in journals and proceedings in cryogenics and superconductivity fields from 1970. The second is to carry out the original experimental researches on He II technologies to obtain new data and to obtain more accurate and reliable data. As for the first sources, we have already picked up about 1, 000 papers and have carried out several experiments. This paper describes the present situation on this research project on the He II database and future plan.
Numerical stability of the heat transfer equation of superfluid helium is discussed in detail for one- and two-dimensional cases. From the viewpoint of diffusive property of heat conduction, the stability conditions for explicit finite difference equations describing the so-called 1/3-power law have been derived. The stability condition depends on the temperature gradient as well as the heat conductivity function and the mesh spacing. To maintain the numerical stability, the time step should be lowered for low temperature gradients. A linearization of the 1/3-power law for low temperature gradients is useful to suppress the numerical instability, but a threshold of the linearization should be selected as low as possible not to affect numerical results. Finally, the validity of the stability conditions is demonstrated by performing two-dimensional numerical simulations of the natural convection of liquid helium with λ-transition.
A two-dimensional calculation code of He II heat conduction, using implicit method, has been developed. It considers a heat conduction equation of He II, omitting some parameters of the two-fluid model. Implicit method can avoid numerical instabilty from a mutual friction term. The computation time and computer power for the calculation can be saved. The temperature distribution of He II for various heat inputs, bath temperatures, and heater lengths may be calculated on a personal computer in short time.
Above the critical power input of the phase transition, the thermoacoustic oscillation is ignited in channels filled with He II at the atmospheric pressure. The clear sound is continuously generated under some conditions of the channel configuration. The characteristic frequency of the thermoacoustic oscillation, which depends on the channel length, is complementarily discriminated by means of a microphone and an oscillatory disk. Except for the thin layer of the triple phase transition near the heated surface, the temperature distribution along the channel length is held during the thermoacoustic oscillation.
The thermal oscillation in the near-saturated He II transports the work through channels above the critical heat flux qc of the phase transition. The oscillation does not entirely destroy the temperature distribution in the vortex state built at qc. Therefore the additional heat input above qc may be efficiently converted into the work flow superimposed on heat conduction, The characteristic frequencies of the thermal oscillation are discriminated by means of an oscillatory disk and a microphone. The thermal oscillation is dominated by the channel length reflecting the nature of the wave.
We study the characteristic features of a superfluid vortex refrigerator especially designed and precisely constructed for NMR measurements of magnetic compounds. The two tubes of superleak and the four chambers are all made of nonmetal substances to reduce eddy current heating because of applied r.f. pulses. A sufficient cooling power for continuous NMR measurements is obtained. The mutual friction between the superfluid component and the normal-fluid component in He II is also discussed.