Numerical Simulation of Quench Propagation in LTS and YBCO 2G Conductors and Coils
- Philippe Masson, University of Houston
Friday, March 15, 11:00 AM - Special Seminar
NSCL Lecture Hall
Superconductors will play an important role in tomorrow’s power systems by enabling the development of more efficient and more compact electrical systems. The unique properties of superconductors allow for current to flow with no resistive losses, however, different types of losses need to be considered in variable regimes and in some cases, thermal runaways (quench) can occur. Quench in superconductors is an electro-thermal instability induced when a local energy input exceeds a certain threshold. It can be created from a multitude of causes including defects in the material, lower critical current or external energy input. A typical local quench starts as a hot spot, creating a local resistive transition of the superconductor forcing the transport current to migrate to the resistive part of the wire; the normal zone propagates along the winding. This phenomenon, very common in low temperature superconductors because the minimum quench energy is very low, is addressed by an active detection system monitoring voltages at different locations. Unfortunately, High Temperature Superconductors (HTS) exhibit very low normal zone propagation velocities (NZPV) making quench detection challenging using conventional voltage-based detection systems. A reliable and quench detection system is critical to the development of power applications of high temperature superconductivity and therefore quench propagation analysis needs to be part of any superconducting magnet design. The peak temperature during a quench strongly depends upon the magnet topology, type of superconductor, current discharge time constant, type of cooling system and operating temperature.
The presentation deals with the simulation of quench propagation using finite element analysis for both LTS and HTS epoxy impregnated coils. The more challenging modeling of YBCO winding is presented at two different scales: at the coil level and at the tape conductors level with an accurate geometry representation. The differences in quench behavior between the LTS and HTS magnets are discussed.