Quench protection for High-Temperature Superconductor (HTS) magnets is essential for their application in High Energy Physics and emerging Fusion technologies. It is a challenging problem due to the slow propagation of the normal zone in HTS materials and the associated difficulties in detecting and mitigating quench development. Meanwhile, HTS conductors are known to operate within a stable dissipative flux flow regime over a wide range of currents, as long as local heat removal prevents thermal runaway. This has led to a quench avoidance approach focused on early detection of dissipation and acting to prevent thermal runaway*. Implementing this approach practically requires real-time distributed temperature monitoring of the HTS conductor and the ability to divert current away from hot spots to keep the conductor below the runaway threshold.
I will focus on two promising distributed temperature sensing techniques currently under development at LBNL. One is the ultrasonic method, which measures thermally induced changes in sound velocity within acoustic waveguides. The other is the radio-frequency method, which detects local temperature-induced permittivity variations in RF transmission lines constructed with custom insulation materials. Practical examples of both techniques and how they can be integrated with HTS magnet coils and cable conductors will be presented. I will also discuss the development of cryogenic MOSFET-based current controls that can redistribute current flow in multi-element HTS conductors or induce AC losses for active protection. The steps for integrating the distributed sensing and current control systems into a closed-loop quench avoidance and protection system will be explained.
*M Marchevsky and S Prestemon 2024 Supercond. Sci. Technol. 37 035012
Lawrence Berkeley National Laboratory, Berkeley, CA, USA