Quench studies on a layer-wound Bi₂Sr₂CaCu₂O_x/AgX coil at 4.2 K

Abstract

To evaluate the controlled quench behavior of high temperature superconducting (HTS) coils, particularly when using HTS coils in a hybrid configuration as an insert in a low temperature superconducting magnet, a layer-wound solenoid using Bi 2 Sr 2 CaCu 2 O wire was instrumented with several strip heaters to generate quenches in the axial and azimuthal directions. An array of distributed voltage taps and thermocouples were used to monitor the quench signals. Minimum quench energies (MQE) and quench propagation velocities (NZPVs) were determined. Results show that quench energies were moderate. NZPVs were slow but quench reaction times were of the same order as reaction times obtained at low quench energy densities in Nb 3 Sn coils.

High-field quench behavior and dependence of hot spot temperature on quench detection voltage threshold in a Bi2Sr2CaCu2Oxcoil

“…Quench behaviors of Ag--sheathed Bi--2212 multifilametnary round wires were investigated using heater--induced experiments in both a solenoid and short length (reacted in 15 cm with ends open and tested in 13 cm) strands. The specifications of the solenoid are summarized in Table 1.…”

“…Quench protection of superconducting magnets, which must detect a non--recovery normal zone and force the magnet current to go to nearly zero within a few seconds or even some fractions of a second to prevent overheating of superconducting windings [9,10], is nontrivial even for superconducting magnet systems made from Nb--Ti and Nb 3 Sn [11,12] for which abundant coil fabrication and operation experiences have been accumulated. It is especially challenging for superconducting magnet systems based on high temperature superconductors (HTS) [13,14] because measurements in short samples of both Bi--2212 [15,16] and (RE)Ba 2 Cu 3 O 7--x (RE = rare earth) coated conductors [17] show that at 4.2 K normal zones propagate at an order of cm/s, instead of m/s for Nb--Ti and Nb 3 Sn at 4.2 K, even in strong magnetic fields ( Figure 1 summarizes propagation speed data of Ag/Bi--2212 round strands and coils available in the literature and measured for this study), limiting our ability to drive the resistive zone to occupy as large a fraction of the winding volume as possible for developing an internal resistance useful for active quench protection. During a quench, conductor temperature rises quickly.…”

“…This knowledge is important for evaluating the effectiveness of voltage measurement for detecting a quench in Bi--2212 magnets and for determining the limits of Bi--2212 magnet technology. Measurements performed so far [15,16,19--21] focuses on determining minimum quench energy and normal zone propagation velocity, and some of these measurement [15] report hot spot temperature, measured by thermocouples that unlikely track temperature rises faster than 10 K/s accurately. This report will present a careful measurement of time evolution of hot spot temperature T max vs. V nz , the normal zone resistive voltage for various J o in magnetic fields, in a Bi--2212 solenoid.…”

Design of a Quench Protection System for a Coated Conductor Insert Coil

“…If it is assumed that the operating current is 260 A, the current density in the copper stabilizer during the quench may reach about 1600 for a standard YBCO tape (copper cross section 0.16 ) and 650 for the tape stabilized 1051-8223/$26.00 © 2011 IEEE with 0.4 copper. For comparison, the current density in a Bi2212 coil [6], whose NZPV is close to the one of coated conductor, was about 420…”

“…The main problem concerning the protection of HTS coils is the slow normal zone propagation velocity (NZPV), which makes it extremely difficult to detect the quench in time. An experimental study of the quench behavior of a Bi2212 coil has been presented in [6]: despite the slow NZPV of few cm/s, the coil could withstand several quenches without damage. Quench experiments have been carried out on various YBCO model coils Manuscript [7]- [10], in order to study the NZPV, the minimum quench energy (MQE) and the general physics of the quench process.…”