An Experimental Setup to Measure the Minimum Trigger Energy for Magnetothermal Instability in $\hbox{Nb}_{3}\hbox{Sn}$ Strands

Abstract

Magneto-thermal instability may affect high critical current density Nb3Sn superconducting strands that can quench even though the transport current is low compared to the critical current with important implications in the design of next generation superconducting magnets. The instability is initiated by a small perturbation energy which is considerably lower than the Minimum Quench Energy (MQE). At CERN, a new experimental setup was developed to measure the smallest perturbation energy (Minimum Trigger Energy, MTE) which is able to trigger the magneto-thermal instability in superconducting Nb 3 Sn-strands. The setup is based on Q-switched laser technology which is able to provide a localized perturbation in nano-second time scale. Using this technique the energy deposition into the strand is well defined and reliable. The laser is located outside the cryostat at room temperature. The beam is guided from room temperature on to the superconducting strand by using a UV-enhanced fused silica fibre. The strand is mounted on a VAMAS barrel. A part of the beam's energy is absorbed into the strand acting as the trigger energy for the magneto-thermal instability. In this paper the experimental setup and the calibration of the absorbed energy is presented.Presented at the 22nd International Conference on Magnet Technology 12-16 September 2011, Marseille, France Geneva, Switzerland CERN-ATS-2012-032February 2012 Abstract-Magneto-thermal instability may affect high critical current density Nb3Sn superconducting strands that can quench even though the transport current is low compared to the critical current with important implications in the design of next generation superconducting magnets. The instability is initiated by a small perturbation energy which is considerably lower than the Minimum Quench Energy (MQE). At CERN, a new experimental setup was developed to measure the smallest perturbation energy (Minimum Trigger Energy, MTE) which is able to trigger the magneto-thermal instability in superconducting Nb3Sn-strands. The setup is based on Q-switched laser technology which is able to provide a localized perturbation in nano-second time scale. Using this technique the energy deposition into the strand is well defined and reliable. The laser is located outside the cryostat at room temperature. The beam is guided from room temperature on to the superconducting strand by using a UV-enhanced fused silica fibre. The strand is mounted on a VAMAS barrel. A part of the beam's energy is absorbed into the strand acting as the trigger energy for the magneto-thermal instability. In this paper the experimental setup and the calibration of the absorbed energy is presented.

Design Optimization, Cabling and Stability of Large-Diameter High Jc Nb3Sn Wires

“…A fuller investigation is needed when evaluating new wire types in order to obtain statistics representative of the performance distribution of the wire. A previously reported approach using a laser to introduce perturbations with a precisely controlled energy [13] will be used to extend this analysis in future work.…”