Electromagnetic drift instability in the 
lower-hybrid frequency range in the reconnection layer

H. Ji, R. Kulsrud, and M. Yamada

By using a local two-fluid theory, we investigate an electromagnetic 
instability in the lower hybrid frequency range driven by cross-field 
current or relative drifts between electrons and ions. The theory 
self-consistently takes into account local cross-field current and 
accompanying pressure gradients. It is found that the instability is 
caused by reactive coupling between the backward propagating whistler 
(fast) waves in the moving electron frame and the forward propagating 
sound (slow) waves in the ion frame when the relative drifts are large. 
The unstable waves propagate obliquely to the unperturbed magnetic 
field and have mixed polarization with significant electromagnetic 
components. A physical picture of the instability emerges as a result 
of further simplifications of the model. The primary positive feedback 
mechanism is based on reinforcement of initial electron density 
perturbations by (de)compression of electron fluid via induced Lorentz 
force. The resultant waves are qualitatively consistent with the 
measured electromagnetic fluctuations in reconnecting current sheet in 
MRX. The resulting resistivity and plasma heating are calculated from 
quasi-liner theory, and within the experimental uncertainties they are 
shown to be quite important for the reconnection process. The 
relationship of these electromagnetic fluctuations to the newly found 
quadrupole out-of-plane field will be discussed.