آذر خسروی

According to previous studies, it is known that Magneto-Rotational-Instability (MRI) can produce turbulent in accretion disks and it can be the origin of viscosity in these systems. These studies showed that MRI can not perform in systems with strong magnetic field. So, the origin of viscosity is as open question in accretion disks with strong magnetic field yet. In this paper, we try to review the instability of accretion plasma disks in the presence of the term including electron pressure in Ohm law. This term can be important in the inner region of accretion disks where the temperature is high and density is low. Some additional terms such as time dependent electrical field and Nernst coefficients are added to equations also. Noted, these terms are neglected in previous studies. Then, the local instability analysis is applied and solutions show that the presence of electron pressure term in Ohm law, can affect the stability of system. According to results, in a system with strong magnetic field (β ≤ 0.1) and without this term, (A = 0), the growth rate of MRI mode is so small,γ <0.2. This result is same as previous result and means that MRI can not perform in accretion systems with strong magnetic field. However, in the presence of this term, A /= 0, result becomes difference. Low A parameter, A ≤ 0.12, can decrease the growth rate of unstable mode to zero and leads to more stability in system. On the other hands, big one, A  0.2 increases the growth rate of unstable mode and leads to more instability in system. So, a system with strong magnetic field, (β = 0.1) can be unstable, γ = 0.7, when the fraction of electron pressure term in Ohm law is big, A = 0.9. These results show that the MRI can be amplified by electron pressure in the inner part of accretion disks and so a system with strong magnetic field can be magneto rotationally unstable in the presence of big electron pressure.