The Use of a Magnetic Field and Magnetic Force as a Means to Improve the Quality of Protein Crystals - Molecules: Nucleation, Aggregation and Crystallization - page 202

is also significant; hence, the product H (grad H ) has a considerable mag-
nitude. In many commercial superconducting magnets, such a position is
found about 100 mm separated from the magnet center. In many cases,
there are two positions that are symmetrically positioned with respect to
the center on both sides. It is at these positions that the effect of the mag-
netic force can best be observed.
Experiments to observe the effects of the magnetic force can be car-
ried out, in the case of using a superconducting magnet, in either a verti-
cally or a horizontally directed bore. If the bore is vertical, then the
direction of the magnetic force is the same as that of gravity; the magnetic
force is either downward or upward. In the former case, the magnetic
force works to strengthen the gravitational pull on Earth. In the latter case,
the magnetic force works to weaken gravity. In the special case where the
magnetic force has the same magnitude as gravity but directed upward,
the magnetic force and gravitational force will be balanced. It is in this
case that feeble magnetic substances “float” within the magnet.
With regard to the direction of the magnetic field, an electromagnet
usually generates a field in the horizontal direction, since a pair of large
and heavy pole pieces are often placed at the same level, i.e. in the left-to-
right direction. A superconducting magnet often has a bore that is vertical.
In this case, vertical magnetic fields are generated at the center of the
bore. The field gradually diminishes above and below the center. In such
a configuration, the direction along which the field gradient is steepest
becomes vertical. It is in this configuration that the upward magnetic force
is generated and can be used to cancel out gravity. However, some super-
conducting magnets can be rotated by 90 around a horizontal axis. If this

operation is carried out, the bore direction becomes horizontal. It is more
difficult for mechanical reasons to direct the bore neither vertically nor
horizontally.

°

Historical Background

As early as 1988, Ryuma Kuroda, who had just entered a graduate course
at the University of Tokyo (Faculty of Engineering, Department of