Magnetic Reconnection Processes Involving Modes Propagating in the Ion Diamagnetic Velocity Direction*

Experiments in weakly collisional plasma regimes, (e.g. neutral beam heated plasmas in the H-regime [1]), measuring the Doppler shift associated with the plasma local rotation [1], have shown that the toroidal mode phase velocity ${\rm v}_{ph}$ in the frame with $E_r=0$ is in the direction of the ion diamagnetic velocity. For ohmically heated plasmas, with higher collisionalities, ${\rm v}_{ph}$ in the laboratory frame is in the direction of the electron diamagnetic velocity, but plasma rotation is reversed as well, and ${\rm v}_{ph}$, in the $E_r=0$ frame, is in the ion diamagnetic velocity direction. Theoretically, two classes of reconnecting modes should emerge: drift-tearing modes [2] and ``inductive modes'' [3] that depend on the effects of a finite plasma inductivity. The former modes, with ${\rm v}_{ph}$ in the direction of the electron diamagnetic velocity, require the pre-excitation of a different kind of mode in order to become unstable in weakly collisional regimes. The second kind of modes has a growth rate associated with the relevant finite ion viscosity. A comprehensive theory is presented. *Sponsored in part by the US DOE.\\[4pt] [1] P. Buratti et al., Nucl. Fusion 52, 023006 (2012).\\[0pt] [2] B. Coppi, Phys. Fluids 8, 2273 (1965).\\[0pt] [3] B. Coppi, Bull. APS 45, 366 (2000).