Technical Papers and Presentations

High-temperature superconductors were discovered in 1986, and it was quickly realised that they could lead to numerous technological breakthroughs. Their high current-carrying capacity has placed them at the centre of today’s fusion race, where they are seen as a key enabler for high-field confinement magnets. Over the past decade, this growing interest in HTS REBCO tapes has made them progressively more commercially available, while simultaneously reducing their cost and improving their performance. This rapid advancement is enabling disruptive solutions across a wide range of sectors, including energy, medical systems, space applications, and high-field magnets.

HTS REBCO conductors exhibit no electrical resistance below their critical temperature when operated in direct current (DC). Nevertheless, even in DC systems, magnets experience transient operation: they must be charged and discharged, and during these processes even HTS conductors experience losses. These transient events must be carefully modelled to estimate the Joule heating and to design the cooling system appropriately.

Modelling REBCO magnets is challenging. First, alternating current (AC) operation requires transient simulations. Second, the superconducting layer is approximately 1 μm thick, while the magnet itself may range from several centimetres to several metres in size. This means that models must bridge multiple orders of magnitude in physical size, quickly becoming computationally intensive. Finally, REBCO performance depends not only on temperature, but also on the current passing through the conductor and the magnetic field magnitude as well as angle, relative to the conductor’s surface.

COMSOL Multiphysics has been extensively used to model HTS devices and has been verified against experimental work numerous times. Combined with its flexibility in allowing users to implement their own partial differential equations, this has made COMSOL Multiphysics a go-to tool for assessing AC losses in HTS devices.

In this presentation, we discuss building a solenoid magnet geometry comprised of a multitude of pancake-wound coils and possible simplifications, meshing techniques, handling the highly non-linear behaviour of HTS conductors, homogenisation techniques, and other methods that can accelerate the simulation of HTS devices, with a particular focus on modelling AC losses.