Numerical Simulation of Microchannel Deformation in Enhanced Insulation for Nb–Ti Superconducting Accelerator Magnets

A new insulation scheme for the Nb–Ti superconducting magnets to better extract heat from the coil was proposed in 2007, and several experiments were done to validate this novel concept, including the construction of a large aperture quadrupole. An essential parameter of this scheme is the size of the microchannels provided by a new topology of the insulation wrapping, allowing a direct helium path from the helium bath to the strands. The main question is whether these channels are still open under the large pressures induced during assembly and by electromagnetic forces. In this paper, one shows that a thermal model of the insulation scheme can be used to interpret the experimental data. The model suggests that the microchannels are significantly reduced with respect to their nominal values but are still well open. To validate this result, a finite-element model of the insulation and strands under pressure is done, and the behavior of this complex topology is estimated. The mechanical model confirms that the microchannels are open even under pressures of 100 MPa, with a cross-sectional reduction on the order of 50%. A parametric analysis of the microchannel deformation versus pressure is carried out, showing a good agreement with the experiments.