Superconducting Heatswitches with Diffusion Bonded Joints

Superconducting (SC) heat switches allow for the on-demand control of a thermal load between objects by exploiting the thermal properties of superconductors in their SC and normal states. Typical approaches for constructing SC heat switches include soldering or mechanically clamping a superconductor with a high conductivity metal, such as copper. In this work, we present the effects of diffusion-bonded aluminum-copper joints on the thermal conductance of a SC heat switch in the closed state. Samples were zero-field cooled to milli-Kelvin temperatures and subsequently driven to their normal state to measure the thermal conductance in the closed state. In-situ calibration was performed to account for any systematic variations in thermometry. The temperature-dependent thermal conductance of a diffusion-bonded SC heat switch was compared to a similar SC heat switch with indium-soldered joints. Preliminary results suggest an improved thermal conductance for the diffusion-bonded SC heat switch. Additional measurements in the open state and with minimum aluminum geometry variations are needed to assess the overall performance of these SC heat switches with different joint mechanisms.