Optimization of wall thickness for water-cooled hollow conductor drive coils in human-sized MPI

Abstract

The reduction and removal of heat dissipated in the drive coil emerges as a major concern when Magnetic Particle Imaging is scaled to human size. The low ac-resistance of Litz wire can reduce the power that generates the heat, but cooling Litz wire bundles can pose a challenge. Hollow conductors with axially flowing coolant present an attractive alternative, but because of skin and proximity effects, the wall thickness is a critical design parameter affecting both the heat created and its rate of removal. Here, we introduce and experimentally validate an analytical method for calculating drive coil heating and optimizing the wall thickness. We demonstrate that the optimal wall thickness provides a 3.3x improvement in cooling efficiency for a fixed pressure with only marginal changes to the coil resistance. A 3.3x improvement in cooling efficiency would allow for ~1.8x more current for the same coil temperature rise, and thus higher drive fields.