Magnetic compensation of gravity forces, similar to the
space conditions of “microgravity”, needs the production of a uniform
magnetic force field. We derive here a basic mathematical result that shows
the impossibility to establish exact gravity compensation in a finite
volume. The imperfection of compensation can be, however, quantified and a
relation is derived between homogeneity accuracy and compensation volume in
a cylindrical symmetry. We study how the use of inserts made of saturated
ferromagnetic materials can modify the homogeneity of magnetic force field.
In order to illustrate this result, an iron insert has been numerically
calculated for the particular case of gravity compensation of H2 in a
10 T superconducting coil. An experimental test has been carried out on a
H2 vapour bubble very close to its gas-liquid critical point. Near the
critical point the gas-liquid interfacial tension is vanishing, then any
bubble deformation from the ideal spherical shape reveals the
non-homogeneities in the magnetic compensation force.