Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

1. Mini-workshop on thermal modeling and thermal experiments for accelerator magnets The modeling of temperature distributions in magnet cross sections with COMSOL Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

2. COMSOL multiphysics (1/3) • Easy implementation of standard problems and the examples in the model library • Straightforward coupling via material properties which depend on results of previous iterations (for example: rho(T) and Iapplied cause Joule heating -> delta T -> rho(T) etc. • Freedom for the user to implement his/her own PDE, material properties etc Chemical reactions Fluid dynamics Heat Electrodynamics MULTIPHYSICS Acoustics Mechanics User defined PDE Erwin Bielert (doctoral student) TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

3. COMSOL multiphysics (2/3) COMSOL uses 5 steps of modeling: • Drawing (or importing) the geometry • Implementing physics (material properties, initial conditions, boundary conditions) • Meshing the geometry • Solving the problem • Post-processing the results Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

4. COMSOL multiphysics (3/3) Problems during the mentioned 5 steps: • Not always straightforward, importing can be a better option (AutoCAD, Inventor, SolidWorks, Pro/E, CATIA) • Material properties in the low temperature range are hard to find and most often, large errors/uncertainties are present • Large differences in characteristic lengths cause large computational effort. Furthermore the order of meshing the domains in 3D is not user friendly • Convergence problems arise without mentioning what the cause is, for inexperienced users this is a major drawback • Good user interface, plenty of possibilities to investigate the results, if necessary results can be exported Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

5. Applications Busbar/interconnect (see presentation A.Verweij) MQXC Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

6. Topics of interest (1/2) Thermal stability at magnet level • Temperature distributions during steady state heat losses • Typical temperature range 1-10K • The maximum temperature at the conductor windings (the temperature margin) must be controlled and this is directly influenced by the overall magnet design • Implemented heat sources are heat leaks, radiation and beam losses (from for example FLUKA) • Low temperature material properties are essential (thermal conductivity, specific heat capacity, density, viscosity) Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

7. Topics of interest (2/2) Quench and ramping of magnets Temperature distribution over time, transient calculations thermal runaway, quench velocity, protection etc. Typical temperature range from 1K to 600K The overall design influences the evolution of temperature and pressure inside the cold mass Joule heating is an additional heat source and is large compared to steady state heat sources Material properties over a much broader range of temperatures are needed (thermal conductivity, specific heat capacity, density, viscosity) Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

8. 2D example: Joule heating andconvective cooling Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

9. 2D purely conductivesimulations MQXC (1/4) Steady state temperature distribution overview Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

10. Thermally open design Idea by G. Kirby conductors void/helium protection sheet kapton fishbone Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

11. 2D purely conductivesimulations MQXC (2/4) Steady state temperature distribution zoom Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

12. 2D purely conductivesimulations MQXC (1/4) Steady state heat flux overview Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

13. 2D purely conductivesimulations MQXC (1/4) Steady state heat flux zoom Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

14. Thermal properties Source: NIST cryogenics CRC handbook of chemistry and physics (86th edition) EFDA material data compilation for superconductor simulation (Bauer et al.) CUDI (Verweij) Bibliographical study (Floch) Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

15. Characteristic lengths/times • The difference in characteristic lengths of some orders of magnitude (FEM intrinsic problem, problems with too fine meshes take too much time to be solved) • In magnets: the thickness of insulation layers (~0.1-1mm) compared to the distance between conductor and heat exchanger (~10cm) Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets

16. Implementation of helium • Effective thermal conduction is dependent on heat flux, which causes a circular dependency • Superfluid heliumflowin complex geometries • 2D approach of collar and iron yoke with averaged bulk properties influenced by packing factor • Passing through Tλ gives convergence problems (like passing Tc in superconductors) Erwin Bielert TE-MSC-SCD Mini-workshop on thermal modeling and thermal experiments for accelerator magnets