The self-electric field effect on the MRI instability of magnetized rotational flows: Cylindrical model

Department of Physics and Institute for Plasma Research, Kharazmi University - 49 Dr. Mofatteh Avenue, Tehran 15614, Iran

Received: 31 May 2017
Accepted: 14 September 2017

Abstract

The self-electric field effect on the magnetorotational instability (MRI) of non-neutral rotating electron-ion plasmas, related to axisymmetric disks, is investigated by using a cylindrical model. Describing the equilibrium state of the rotational system in the presence of a self-electric field, the fluid-Maxwell equations as well as the linear perturbation theory are employed to derive the dispersion relation (DR) of the excited modes in the system. The obtained DR analysis leads to analytical stability conditions, the growth rate of the instability, and the saturation amount of the pure instability excited in the system, depending on the equilibrium velocity difference between the involved components. Moreover, the numerical analysis of the obtained DR shows that the self-electric field has an important role for the MRI in the region where the angular frequency due to drift, , dominates over all the frequencies, in the outer part of non-neutral disks. In this region, the growth rate of the MRI increases dramatically with the ratio of the ion density to electron density until it saturates. On the other hand, in the inner region of the disk in which the gravitational frequency overcomes the others, the growth rate of the instability is found to be much smaller than that of the outer region. These results can be applicable to understand the MRI growth rate of the differentially rotating non-neutral plasma systems existing in the astrophysical environments, particularly in the magnetosphere of a neutron star.