In the thermal design of high magnetic field superconduct
ing accelerator magnets, the emphasis is on the use of
superfluid helium as a coolant and stabiliz
ing medium. The very high effective thermal conductivity of
helium below the lambda transition temperature significantly helps to extract
heat from the coil w
ind
ings dur
ing steady state and transient
heat deposition. The layout and size of the
helium channels have a strong effect on the maximum amount of
heat that can be extracted from the porously
insulated superconduct
ing cables. To better understand the behavior of
superfluid helium penetrat
ing the magnet structure and coil w
ind
ings, simulation based on a three dimensional f
inite element model can give valuable
insight. The 3D geometries of
interest can be regarded as a complex network of coupled 1D geometries. The govern
ing physics is thus similar for both geometries and therefore validation of several and different 1D models is performed. Numerically obta
ined results and published experimental data are compared. Once the viability of the applied methods is proven, they can be
incorporated
into the 3D geometries. Not only the transport properties
in the bulk of the
helium are of
interest, but also the strong non-l
inear behavior at the
interfaces between solids and
superfluid helium (Kapitza conductance) is important from an eng
ineer
ing po
int of view, s
ince relatively large temperature jumps may occur here.
In this work it is shown how He-II behavior in magnet windings can be simulated using COMSOL Multiphysics. 1D models are validated by experimental results taken from literature in order to improve existing 2D and 3D models with more complete physics. The examples discussed include transient heat transfer in 1D channels, Kapitza conductance and sub-cooling of normal liquid helium to temperatures below the lambda transition in long channels (phase front movement).