Vector Fields Ltd., Oxford
* M. N. Wilson, Superconducting magnets p217ff
** S. Caspi et Al, Calculating Quench propagation with Ansys, IEEE Trans. Appl. Supperconduct. Vol 13, No2, pp1714-1717
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| MOAPMP01 | Coupled Transient Thermal and Electromagnetic Finite Element Simulation of Quench in Superconducting Magnets | simulation, electromagnetic-fields, target, controls | 70 | |||||
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Resistive, normal zones may propagate through the low temperature superconducting coils. The rise in temperature in the windings and the internal voltages developed during this quench process are a critical issue for magnet safety, in addition the eddy currents induced in support structures during a quench may result in large Lorentz forces that can cause damage. Approximate adiabatic models have been used to achieve good results for the time profile of the current decay*. More accurate methods based on finite element simulations have also been used to obtain temperature and voltage distributions**. This paper describes transient, closely coupled thermal, electromagnetic finite element and circuit simulations developed to model quenching magnets. The program was designed to be efficient for this calculation. It uses nodal finite elements for the transient thermal simulation and edge elements for the electromagnetic simulation. The two simulations can be performed on different symmetry groups so that the model size can be minimized. Circuit models are coupled to the electromagnetic simulator either using filamentary edge loops or with a full volume mesh in the coils. Accurately meshing the coils increases the model size, but it is essential if accurate fields and time derivatives of the field are required. The main source of heat in the coils during quench is resistive loss in the normal zone. However rate dependent losses caused by the changing magnetic field may cause heating and therefore trigger a quench in other coils. Having closely coupled thermal and electromagnetic simulations makes it easy to include these effects and hence greatly improves the reliability of the simulation. Calculated and measured results for a 4 coil superconducting polarized target magnet will be presented. In this system the quench spreads to another coil as a result of rate dependent losses, the calculated results change dramatically if these losses are not included.
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* M. N. Wilson, Superconducting magnets p217ff |
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