Large sample study and modeling of three dimensional magnetic reconnection at SSX

We have recently been performing large sample statistical studies of magnetic reconnection at SSX. We have over 600 merging events in our sample so far. The experiment generates two fully ionized relaxed MHD hydrogen plasmas which move towards each other with approximate velocity v = 30 km/s. The magnetic field in the reconnection region is measured with a planar 4x4 array of B-dot probes. The line averaged electron density in the center of the reconnection region is measured using Mach-Zehnder interferometry. Ion temperature is measured using ion Doppler spectroscopy. Typical SSX plasmas have B = 0.3 T , ne = 4 × 1015 cm−3, and Ti = 40 eV. Current density is calculated in the plane of the probe array using the curl of the magnetic field. In addition, we have added a heterodyne interferometer to compare with our Mach-Zehnder measurement. We are using the Dedalus framework, an open-source flexible spectral method Python framework, to simulate MHD time evolution of two spheromaks merging in a cylindrical 1:10 chamber. We use CFL dynamic time stepping in a 64x64x320 resolution Cartesian grid, with periodic boundary conditions. Temperature is initialized proportionally to density under ideal gas assumptions. Typical magnetic Reynolds number Rm ≈ 1000 and mechanical Reynolds number Re ≈ 200. The vector potential is initialized from the force-free equation ∇ × B = λB and given a perturbation to break axial symmetry. The simulation runs for ~20 Alfvén times during the reconnection event, with the spheromaks merging in the midplane at ~5 Alfvén times.