Dependence of magnetic reconnection on ion gyroradius during the super-Alfvénic/sonic collisional merging process of field-reversed configurations*

The observation of the magnetic reconnection during the super-Alfvénic/sonic collisional merging process of field-reversed configurations (FRCs) is being attempted in the FAT-CM device. In the collisional merging formation of FRCs, two FRC-like initial-plasmoids collide at a relative speed that exceeds both the typical Alfvén speed and the ion sound speed, then they merge into one FRC [1]. The fast magnetic reconnection may occur during the collisional merging process which is completed in around 20 microseconds. In collision-less plasmas, the finite Larmor radius effect is considered to be one of the mechanisms that dissipates the magnetic flux and causes fast magnetic reconnection at Alfvén speed. In this work, the low-density FRC formation technique [2] is applied to the formation of dilute and high-temperature initial-plasmoids to control the ion gyroradius. The reconnection process is observed using the fast-framing camera (ULTRA Cam HS-106E, nac Image Technology Inc.) with a bandpass filter. The dependence of global behavior of the magnetic reconnection on ion gyroradius will be presented.

[1] T. Asai et al., Nucl. Fusion 59, 056024 (2019).

[2] Y. Ohkuma et al., Nucl. Fusion 38, 1501 (1998).