The design of a compact conduction-cooling system for SRF material characterization

The precise and efficient testing of the RF performance of superconducting radio frequency (SRF) samples under superconducting conditions serves as the fundamental support for developing new SRF materials. The traditional SRF material RF performance testing systems have technical bottlenecks such as strong dependence on liquid helium, long testing cycles, and high operating costs. In this paper, the design and Multiphysics simulation analysis of a novel conduction-cooling RF performance testing system for SRF materials are presented. The system is numerically predicted to achieve 50 mT and n <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> </mml:mrow> </mml:math> -level measurement of the surface resistance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m2"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> without liquid helium cooling. The core part of the system is an optimized mushroom-type sample host cavity, which operates primarily in the 3.9 GHz <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m3"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>TE</mml:mtext> </mml:mrow> <mml:mrow> <mml:mn>011</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> mode, with a sample radius of 33 mm. A <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m4"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mtext>Nb</mml:mtext> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> Sn coating on the inner cavity surface is proposed in the design to lower microwave loss, and the entire conduction-cooling structure is engineered and analyzed numerically. Additionally, the resolution and measurement range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m5"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> are systematically evaluated via Multiphysics simulations, showing the potential of the design for low-cost, high-quality SRF material characterization.