Magnetic reconnection is a ubiquitous and important process throughout the Universe. It explosively reconfigures the topology of magnetic field lines, and enables the rapid dissipation of magnetic energy, heating and accelerating the plasma. This process has been studied in both space and laboratory experiments, including the collisionless regime relevant to the solar wind. In recent years, high energy density experiments driven by lasers or pulsed-power have further expanded the plasmas in which we can study reconnection.

In particular, recent pulsed-power experiments have demonstrated the development of the plasmoid instability, a tearing of the reconnecting current sheet, which leads to very rapid reconnection and dissipation of the magnetic energy. Although in the purely MHD regime plasmoids are predicted to develop only at high Lundquist numbers (a dimensionless measure of plasma conductivity), recent theoretical work has demonstrated the existence of a semi-collisional regime, in which two fluid effects are important, which enables plasmoids to form at much more modest conditions. In addition, the significant density perturbations present in these experiments and in real astrophysical plasmas may enable plasmoids to form at lower Lundquist numbers than As such, these pulsed-power experiments offer a qualitative window into the plasmoid instability, which is believe to be important in reconnection throughout the Universe.

Recently, MIT graduate student Thomas Varnish has been developing a platform to study guide-field reconnection, in which there is an out-of-plane component to the magnetic field in addition to the anti-parallel reconnecting fields. We tested two iterations of this platform on the MAIZE pulsed-power facility at the University of Michigan, first using an externally applied magnetic field from a pulsed Helmholtz coil, and then with tilted wire arrays to embed the guide field in the plasma flows. Further experiments using this platform will be carried out on PUFFIN and COBRA.

We are grateful to the NSF and NNSA for supporting graduate student Thomas Varnish through award PHY2108050, “Developing Pulsed Power Driven Turbulent Reconnection Platforms”.

Further Reading