Observed Suppression of Self-Generated Magnetic Fields in a Laser-Driven Cylindrical Implosion *

A cylindrical implosion using the mini-MagLIF platform at the Omega Laser Facility used oblique proton radiography to measure self-generated magnetic fields produced by the Biermann battery mechanism in the coronal plasma. Proton radiography oblique to the axis of the cylindrical target allows axially resolved measurements of self-generated azimuthal magnetic fields, which are not possible at normal incidence. These experimental measurements are compared to synthetic proton radiographs generated by the PlasmaPy proton radiography module [1] using fields from three-dimensional HYDRA simulations. This comparison shows that magnetohydrodynamics (MHD) overpredicts the self-generated field by a factor of ~2 to 3. Simulations also show that collisionality is low in the region where the fields are generated, suggesting that nonlocal effects may be responsible for the discrepancy. This result provides experimental evidence for previous theoretical predictions that nonlocal effects can result in suppressed self-generated magnetic fields relative to MHD.

 

[1] PlasmaPy Community et al., PlasmaPy (Version 0.6.0), Zenodo, Accessed 14 March 2021, http://doi.org/10.5281/zenodo.4602818.