High-field quench behavior and dependence of hot spot temperature on quench detection voltage threshold in a Bi2Sr2CaCu2Ox coil

• Published in: Superconductor science & technology Vol. 28; no. 7
• Main Authors: Shen, Tengming, Ye, Liyang, Turrioni, Daniele, Li, Pei
• Format: Journal Article
• Language: English
• Published: United States IOP Publishing 15.06.2015
• Subjects: Bi-2212 magnet; PARTICLE ACCELERATORS; quench behavior; quench detection; quench protection; superconducting magnets
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/28/7/075014

Small insert solenoids have been built using a multifilamentary Ag Bi2Sr2CaCu2Ox round wire insulated with a mullite sleeve (∼100 m in thickness) and characterized in background fields to explore the quench behaviors and limits of Bi2Sr2CaCu2Ox superconducting magnets, with an emphasis on assessing the impact of slow normal zone propagation on quench detection. Using heaters of various lengths to initiate a small normal zone, a coil was quenched safely more than 70 times without degradation, with the maximum coil temperature reaching 280 K. Coils withstood a resistive voltage of tens of mV for seconds without quenching, showing the high stability of these coils and suggesting that the quench detection voltage should be greater than 50 mV in order not to falsely trigger protection. The hot spot temperature for the resistive voltage of the normal zone to reach 100 mV increased from ∼40-∼80 K while increasing the operating wire current density Jo from 89 A mm−2 to 354 A mm−2, whereas for the voltage to reach 1 V, it increased from ∼60-∼140 K. This shows the increasing negative impact of slow normal zone propagation on quench detection with increasing Jo and the need to limit the quench detection voltage to <1 V. These measurements, coupled with an analytical quench model, were used to assess the impact of the maximum allowable detection voltage and temperature upon quench detection on the quench protection, assuming a limit of the hot spot temperature to <300 K.