Study of Waves and Hall Effect in Reconnecting Current Sheet in a Laboratory Plasma

Magnetic Reconnection is thought to play an important role in affecting magnetic topology, plasma heating, and particle acceleration. A key question about the reconnection process is why the reconnection rates are much faster than predictions by the Sweet-Parker model. There exist two competing theoretical mechanisms: one based on decoupled ion and electron motions (the so-called Hall effect) and another based on enhancement of dissipation due to waves. In a well-controlled laboratory plasma in the magnetic reconnection experiment (MRX), signatures for both mechanisms have been detected during fast reconnection process: the existence of an out-of-plane quadrupole field and electromagnetic fluctuations up to the lower-hybrid frequency range. In this paper, we report experimental results on relationship between these two phenomena, as well as their relationship with the reconnection process. Preliminary analyses indicate that fluctuations tend to appear at the formation stage of current sheet with strong drive while out-of-plane quadrupole field tend to appear clearly during quasi-state reconnection process with relatively week drive. In addition, a small coil is inserted into the current sheet to actively drive electromagnetic waves as a function of frequency and orientation with respect to the reconnecting magnetic field. Measurements of wave propagation and amplification/damping will be reported. This work is supported by NASA and DoE.