Speaker
Description
Quenches are a major issue for superconducting magnets because of their high current density which translates to high stored magnetic energy and eventually heat dissipation that may cause irreversible damage if left unadressed. Designing a well-protected magnet against quenches is one of the key considerations in the design. The objective of this paper is to describe the experimental demonstation of a novel quench detection and protection principle, combining a superconducting coil with a co-wound normal-conducting secondary coil. Similar to a co-wound voltage tap, the presence of the secondar coil allows for inductive noise suppression, thus facilitating low-noise quench detection. After quench detection, discharging the superconducting coil over an energy extractor featuring diodes and resistors gives rise to a very quick initial discharge of the superconducting coil. Following the quench-back principle, the induced currents in the secondary coil quickly heat up the cold mass and trigger a homogeneous quench. A major benefit of this quench protection principle is that, compared to quench protection configuration featuring energy extraction without quench-back, the needed voltage over the energy extractor is reduced by more than one order of magnitude.
To experimentally demonstrate the principle, a demonstrator magnet consisting of co-wound NbTi and Cu coils with an open warm bore size of 400 mm was assembled and tested. During testing the magnet was ramped to nominal current of 200 A without training quenches while producing a B-field of 1 T at center bore. The operational parameters were measured and found to agree with simulations and calculated results. The detection threshold voltage of quenches is verified at common electromagnetic noise-inducing frequencies by an inductively coupled pick-up coil paired with a signal generator.
The quench detection and protection method is expected to not just be beneficial for low-temperature superconductors, but also high-temperature superconductors, where quench detection at low threshold voltages is an important attribute to have. This paper describes how these principles can be scaled to higher field low- temperature superconducting or future high-temperature superconducting (HTS) detector magnets.
