Using magnetic levitation to produce cryogenic targets for inertial fusion energy: experiment and theory

We present experimental and theoretical studies of magnetic levitation of hydrogen gas bubble surrounded by liquid hydrogen confined in a semi-transparent spherical shell of 3 mm internal diameter. Such shells are used as targets for the Inertial Confinement Fusion (ICF), for which a homogeneous (within a few per-cent) layer of a hydrogen isotope should be deposited on the internal walls of the shells. The gravity does not allow the hydrogen layer thickness to be homogeneous. To compensate this gravity effect, we have used a non-homogeneous magnetic field created by a 10 T superconductive solenoid. Our experiments show that the magnetic levitation homogenizes the thickness of liquid hydrogen layer. However, the variation of the layer thickness is very difficult to measure experimentally. Our theoretical model allows the exact shape of the layer to be predicted. The model takes into account the surface tension, gravity, van der Waals, and magnetic forces. The numerical calculation shows that the homogeneity of the layer thickness is satisfactory for the ICF purposes.