  A high-density magnetized plasma has been studied for understanding of plasma
dynamics in partially ionized plasmas. Ion flow field has been obtained
experimentally, and is shown to be associated with a vortex formation. The most
remarkable result is that the direction of rotation is opposite to that of the
ExB drift. Measurement of neutral density profile reveals that there is a steep
density gradient of the neutrals around the vortex, suggesting that the
generation of inward momentum of the neutrals due to the density gradient. The
momentum is transfered to ion with charge-exchange collision, and cause
effective force on the ion. The present experiment shows that this effective
force may dominate the ambipolar-electric field and drive the anti-ExB vortical
motion of ions.
