  A two-fluid flowing plasma model is applied to describe the plasma rotation
and resulted instability evolution in magnetically enhanced vacuum arc thruster
(MEVAT). Typical experimental parameters are employed, including plasma
density, equilibrium magnetic field, ion and electron temperatures, cathode
materials, axial streaming velocity, and azimuthal rotation frequency. It is
found that the growth rate of plasma instability increases with growing
rotation frequency and field strength, and with descending electron temperature
and atomic weight, for which the underlying physics are explained. The radial
structure of density fluctuation is compared with that of equilibrium density
gradient, and the radial locations of their peak magnitudes are very close,
showing an evidence of resistive drift mode driven by density gradient.
Temporal evolution of perturbed mass flow in the cross section of plasma column
is also presented, which behaves in form of clockwise rotation (direction of
electron diamagnetic drift) at edge and anti-clockwise rotation (direction of
ion diamagnetic drift) in the core, separated by a mode transition layer from
$n=0$ to $n=1$. This work, to our best knowledge, is the first treatment of
plasma instability caused by rotation and axial flow in MEVAT, and is also of
great practical interest for other electric thrusters where rotating plasma is
concerned for long-time stable operation and propulsion efficiency
optimization.

Plasma Physics