A numerical model for stability considerations in HTS magnets

We propose that in an HTS application, stability is lost more likely becaus e of a global increase in temperature caused by heat generation distributed over the whole coil than because of a local normal zone which starts to pr opagate. For consideration of stability in HTS magnets, we present a comput ational model based on the heat conduction equation coupled with Maxwell's equations, whereby analysis can be performed by using commercial software p ackages for computational electromagnetics and thermodynamics. For temperat ure distribution inside the magnet, we derive the magnetic held dependent e ffective values of thermal conductivity, specific heat, and heat generated by electromagnetic phenomena for the composite structure of the magnet, whi le cooling conditions and external heat sources are described as boundary c onditions. Our model enables the magnet designer to estimate a safe level o f the operation current before a thermal runaway. Finally, as examples, we present some calculations of the HTS magnet with ac to review the effects o f slanted electric field-current density E(J) characteristics and high crit ical temperature of HTS materials.