Hiromichi Uetake

Nonmechanical magnetothermal wind blower by a superconducting magnet

A magnetothermal wind blower without mechanical driving parts is demonstrated up to a velocity of about 0.5 m/s (4 l/min). The wind was created in a ceramic tube, 13 mm i.d., with an external heating coil, and placed in a superconducting magnet with a maximum field of 8 T. The heat zone was at an off-maximum position of the magnetic field distribution. The magnetic forces exerted on the slightly paramagnetic air by the field gradient at the two sides of the magnet center were out of balance due to the asymmetrical heating, thereby creating a net air flow which was detected by the slanting of a candle flame and by measurements of the temperature distribution in the air. The wind direction was such that the warmer air was expelled from the magnet while the cold air was sucked into it. The wind velocity could be quantitatively interpreted by considering the viscous flow of the air driven by the magnetic force imbalance.

Separation of feeble magnetic particles with magneto-Archimedes levitation

Abstract Particles and solid substances with feeble magnetic susceptibility were levitated by magnetic fields with the aid of the “magneto-Archimedes levitation” method [Nature 393 (1998) 749]. A novel feature was found, namely that the initial particle mixture levitated underwent separation into each kind of the ingredient particle aggregates. The samples levitated were NaCl–KCl grain mixtures, and colored glass particles. The experiments below are made with two different compact superconducting magnets with the maximum field of 10 and 12 T. In this study, the two methods, conventional diamagnetic levitation and magneto-Archimedes levitation are comparatively discussed, and the novel magnetic separation is described.

Magnetic field effects on water, air and powders

Magnetic fields up to 10 T have been applied on various substances composed of non-magnetic liquids, solids and/or gases. It has turned out that the magnetic fields of this range do produce various visible effects on the equilibrium shape, relative distribution of the substances or kinetic processes of the systems. The phenomena observed are due to the magnetization force that becomes non-significant in determining the mechanical balance of the system. The effects manifest themselves through the deformation of the equilibrium shape of the liquid interfaces, through the change in the effective weight which determines the relative positions occupied in the space by the substances involved and through the creation of convection in a non-uniform gas or liquid phase in terms of the magnetic susceptibility. Some of the processes seem to be utilized for practical purposes.

Thermal convection control by gradient magnetic field

A new technique to control thermal convection has been demonstrated by utilizing a gradient magnetic field. When the center of the superconducting magnet was fixed below the center of the heating region, the thermal convection flow was accelerated. In contrast, the convection flow was suppressed when the field center was fixed above the heating center, and under certain conditions, a reverse direction of flow was observed. The control of the flow was made possible by the experimental procedure, in which a downward flow was induced when the magnetic field was applied prior to the heating, and an upward flow was observed under the reverse procedure. These phenomena can be understood by taking account of the balance between the thermal driving force and the magnetic force acting on the air. A detailed analysis was made by examination of the temperature distribution in the observed system. The results suggest the possibility of using a gradient magnetic field for controlling thermal convection without any mec...

Self-organization of nonmagnetic spheres by magnetic field

Two-dimensional crystallization of nonmagnetic gold spheres was achieved by the application of a high magnetic field. This phenomenon is based on the two different forces caused by a magnetic field; interactions between magnetic dipoles induced in the nonmagnetic spheres and magnetic force derived from field gradient. The former force is generally so weak and, hence, negligible. However, under an appropriate condition, we can achieve the subtle balance between the two forces. This phenomenon is a new class of self-assembling phenomena, and we believe that our achievement will be a milestone in the utilization of magnetic fields.

Magnetic-field simulation for shielding from high magnetic fields

Magnetic-field simulations have been carried out to attain efficient magnetic shielding from high and static magnetic fields. A stray field created by a 10 T solenoid superconducting magnet with a φ100 mm room-temperature bore was assumed. As a shielding material, plate-, cylindrical-, and the combination of a plate- and framework-shaped irons were selected. To investigate the effect of the iron shield, the shielding factors were evaluated systematically by changing the shape, size, thickness, etc. of the shield emphasizing the area around 2 m apart from the field center in the axial direction. Various simulations led us to conclude that the shielding factor becomes high because of the use of large iron plates and not because of either the thickness or the number of layered plates. Then, the combination of a iron plate and framework was suggested and examined as a way of efficient shielding. On the other hand, when the shield was placed in the radial direction, the larger and the thicker the shield became...