Cooling efficiency and thermal stability is strictly demanding for practical applications of superconductors operating at current values close to the critical current, such as superconducting detectors. Indeed, a thermally unstable device can show premature quench, i.e. it can suddenly switch from the superconducting state to the normal one at a current value lower than the expected one, which can result in false counts. Cooling by direct contact with a liquid He bath is considered the best way to obtain thermal stability in a superconducting device. Other, cheaper cooling techniques can be suitable to achieve satisfactory working conditions. In this work, we evaluate the impact of three different cooling environments, namely liquid He in a standard cryostat and both dynamic and static He gas in a cryogen-free cryostat, on current voltage characteristics (CVCs) acquired in ultra-thin superconducting microbridges suitable for detectors. In particular, we use the Flux-Flow Instability phenomenon as a tool to analyze voltage stability in CVCs in the three different environments and we find that cryogen-free techniques have performance comparable to liquid He cooling.
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