Calculation and simulation of shielding systems for the protection of superconducting electronic circuits from IR radiation
The operation of superconducting electronic circuits is influenced by IR radiation coming from outside. To protect electronic circuits from radiation, shielding systems consisting of several nested shields covered with absorbing coatings are used. Due to the variety of materials used and of the shields sequence, it becomes difficult to choose the most effective shielding system. In this work, a calculation on a base of radiative heat transfer theory and finite element simulation results of several shielding systems for the protection of superconducting circuits from IR radiation are provided. It was demonstrated that the main source of IR photons in the measuring system of superconducting circuits is radiation propagating along wires, as well as released on passive circuit elements and on a chip in the form of heat. The most effective shielding system for various radiation sources was determined by two methods. Calculation and simulation have shown that the greatest influence on the temperature of the quantum circuit is exerted by the surface closest to the sample - the holder lid; therefore, it must be made absorbing. It has been established that the shielding from IR radiation by means of the holder lid surface is sufficient. Based on the simulation, recommendations for choosing a holder design for a quantum circuit have been formulated: for the best protection of a sample with a superconducting electronic circuit, the lid should cover only the chip and the gap between the holder bottom and the holder lid should not exceed 0.1 mm.