Observation of magnetic field structure during the supersonic spheromak merging process*

The supersonic spheromak (Spk) merging device [T. Matsumoto et al., Rev. Sci. Instrum. 89, 10E108 (2018)] to observe a magnetic reconnection process involving shockwave generation, and the formation of field-reversed configuration (FRC), is being developed at Nihon University.The device consists of two magnetized coaxial plasma guns (MCPG) [T. Asai et al., Nuclear Fusion 57, 076018 (2017)], [T. Edo et al., Plasma and Fusion Research 13, 3405062 (2018)], a transparent quartz chamber, and four external magnetic field coils. Spk-like magnetized plasmoids, generated and accelerated by each MCPG, are injected from opposite ends of the quartz chamber, where they collide and merge. The injection speed of approximately 40–60 km/s was achieved. So that the relative speed will be 80–120 km/s. This speed corresponds to a Mach number of approximately 1.2–2 based on the Alfvén/ion sound velocity. To realize supersonic Spk merging, the injected plasmoids will be evaluated and compared. In this work, a new internal magnetic probe capable of measuring magnetic field vectors in three directions will be developed. This probe will observe the internal magnetic field structure during the collision and merging processes, evaluate the magnetic reconnection process with supersonic inflow, and determine the conditions for FRC formation.