Calculation of the Cryogenic Loads on a Superconducting RF Module

The thermal radiation of a superconducting RF (SRF) module is simulated using software (ANSYS FLUENT) for three-dimensional computational fluid dynamics (CFD). The heat radiating from beam tubes and an input-power coupler (of waveguide type) of the SRF module into the 500-MHz niobium cavity is calculated simultaneously with partially diffuse and partially specular reflection. The total heat loads on liquid helium (LHe) and liquid nitrogen (LN2) are estimated on introducing both radiation and conduction. This estimated total heat load on liquid helium is verified with a direct experimental measurement of the heat load; the calculated results match the measurement data. The radiative surface properties are investigated on varying the magnitude of the diffuse fraction of surfaces to assess the effect of the surface condition on the thermal radiation; a tabulated list of total heat load is given to understand how most effectively to decrease the cryogenic load of an SRF module. Our results provide guidance for selecting in advance a surface treatment and the direction of design to minimize the cryogenic load from radiated heat.