History and theoretical design equations for the ferromagnetic shielding which has been generally used for biomagnetic measurement are described. Methods of demagnetization are reviewed, which are needed for the improvement of shielding performance. The main features of the large magnetically shielded room for operation with SQUID systems in medical research and diagnosis in the near future are also described. Finally, high performance shielded room which is under construction at SSL is presented.
Immersion cooling of a coated metallic object is discussed. Paradoxically, a coated object cools quicker than when the same object is bare. Through this phenomena the reader is introduced to various related topics. The main subject in the first issue is about the stability of the interface between liquid and vapor around the object and how this instability causes an early transition from film boiling to nucleate boiling state. In the second issue, the reader is introduced in more detail to film boiling by taking up the issue of film boiling on a long flat heater. A model for film boiling on such a heater is cited and effects of heater orientation and temperature on film boiling are qualitatively described based on this model. Finally, heat transfer in subcooled forced-flow helium is compared with that of supercritical helium, and ranges of heat flux are discussed for effective use of these two types of helium heat transfer.
A 20T large bore superconducting magnet has been developed at the National Research Institute for Metals. In this paper, design for its coils is mainly discussed. Design policy for this magnet system is to meet two contradicting requirements; large bore diameters and generation of high magnetic fields. The magnet consists of four coils, and should be operated at 1.8K in saturated superfluid helium to generate its highest field. Magnetic fields of 15T in a 314mmφ thermally insulated chamber, of 18T in a 160mmφ bore and of over 20T in a 44mmφ bore are designed to be generated with combinations of these four coils.