We report a study of the variation and compensation of gravitational forces in diphasic (p‐) hydrogen. The sample is placed on the axis of a superconducting coil near one of the ends, in order to benefit from a nearly uniform magnetic field gradient. A variable reduced effective gravity g* can thus be applied to the fluid. It is shown that the exact compensation of gravitational forces (“weightlessness conditions”) is limited by the inhomogeneity of the magnetic field gradient, which consists of a radial force field centered on the point of compensation and varying proportionally with the distance from this point. Such inhomogeneities can be quantified by an associated capillary length (lC). The effect of this remaining field is negligible when lC is smaller than the cell dimension. Near the critical point, the length lC tends to zero and the gas-liquid interface is deformed in a paradoxical pattern, in which the liquid phase lies at the center of the container with the gas phase at the walls. We vary the effective gravity g* and determine in a wide range of reduced temperature τ=(TC−T)/TC=[10−4−0.02] the corresponding capillary length lC from a fit of the interface profile. The data complement previous measurements in n-H2 at g*=1, performed further from TC.

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