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

Abstract

Coated conductors are promising material for the construction of high field magnets, but the slow propagation velocity of the normal zone makes the protection against quenches a critical issue. The quench protection system for a small insert coil under development at CRPP has been studied. The voltage drop and the hot spot temperature during the quench have been estimated using analytical expressions; the cross section of the copper stabilizer, the voltage threshold and the time constant were set as parameters. Detailed calculations have been carried out using the Cryosoft code THEA. The copper cross section available from the tape manufacturer is enough to ensure that the hot spot temperature remains below 200 K, but only in conjunction with a sensitive quench detection system (voltage threshold lower than 100 mV) and a fast dumping time (time constant shorter than 100 ms). These requirements can be fulfilled in the small insert coil under construction, because the inductance is about 50 mH and because the coil can be quickly discharged independently from the main magnet. The passive protection circuit consists of dump resistor and diodes. In case of longer time constants (few seconds), a larger copper cross section (comparable to the one used in low temperature superconducting magnets) is required in order to maintain the temperature within safe values.

Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

“…One obvious step that may be undertaken is to increase the thickness of the metal stabilizer in order to be able to reduce the rate of heating at the developing hot spot. The effectiveness of this approach is demonstrated, for example, in [97], where the increase of the copper stabilizer cross-section in the ReBCO conductor from 0.16 mm 2 to 0.4 mm 2 yielded a two times reduction of the hot spot temperature in the current dump experiment on an HTS insert coil. An obvious drawback of this approach, however, is that the proportionally reduced engineering current density of the conductor reduces the magnet performance.…”

Progresses and challenges in the development of high-field solenoidal magnets based on RE123 coated conductors

“…Ishiyama et al, worked out general equations to estimate the optimal stabilizer cross-section for a SMES magnet operated at 50 K [133]. Regarding high-field coils, simulation study by Uglietti and Marinucci has shown that a moderate increase in copper cross-section coupled with a sensitive quench detection and a short discharge time constant are sufficient to passively protect a 4 T/40 mm bore magnet [134]. For large coils the copper cross-section should be further increased if a passive protection system (shunt resistors with diodes) is used.…”

AMS-100: The next generation magnetic spectrometer in space – An international science platform for physics and astrophysics at Lagrange point 2

“…It has been shown in Ref. [25] that increasing the stabilizer thickness aids in reducing the magnet temperature at a quench. For the AMS-100 magnets, we assume that the copper stabilizer will be replaced by an equivalent aluminum stabilizer to minimize the material budget [26].…”