Finite element modeling of vacuum magnetic fields for the TREX drive cylinder using COMSOL*

The Terrestrial Reconnection EXperiment (TREX) [1] at the Wisconsin Plasma Physics Laboratory (WiPPL) [2] aims to explore the kinetic collisionless regime of magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has made in situ measurements of anisotropic electron distributions in this regime [3], and the upgraded TREX drive cylinder may be able to recreate these observations in a laboratory setting. This is accomplished by lowering the system's inductance, reducing the electron fluid crossing time to a level comparable to the electron-ion collision time (~1 μs). Additionally, a cylinder composed of 40 aluminum plates shields the radial component of the magnetic field, supporting the development of current layers up to ~2 m. The electric and magnetic fields were modeled using COMSOL Multiphysics, validating the design's functionality. COMSOL uses a finite-element method to model the drive cylinder geometry, allowing us to implement the appropriate time dependence of the coil current and numerically compute the fields from Maxwell's equations. Finally, the model provides an estimate of the magnetic diffusion time of the drive cylinder of ~2 ms, allowing us to approximate the plates as perfect conductors for the duration of the ~10 μs experiment.