Numerical study of the thermal field in a cryostat for nuclear magnetic resonance imaging

In this paper, we present the preliminary results about the thermal field inside the cryostat, obtained by finite element numerical simulations performed in Comsol Multiphysics environment. The simulations concern simplified three-dimensional geometries obtained from field inspections and construction schemes; sizes and materials actually used and all modes of heat transfer are taken in account. We discuss some configurations of thermal insulation and boundary conditions able to simulate the effect of a "cold head" placed in contact with a very limited portion of the cryoshields. Finally, we show results about the thermal field when tie rods are mounted that in real cryostats allow to mantain the empty cavity and to center the magnetic field.