Nonlinear structures in a protoplanetary disk Murchana Khusroo and Madhurjya P Bora Department of Physics, Gauhati University, Guwahati-14, Assam, India I. Introduction Balbus and Hawley, in 1991, were able to explain that accretion disks undergo a powerful shearing instability transmitted by a weak magnetic field that is responsible for the origin of turbulent viscosity in accretion disks, which they termed as magnetorotational instability (MRI) [1]. In a protoplanetary disk system (PPD), various nonlinear magnetic activities that are taking place, are strongly subjected to non-ideal magnetohydrodynamics (MHD) effects due to the low ionisation of the disk plasma. Inutsuka and Sano, in 2005, showed that in a weakly ionised PPD, the MRI-driven turbulence produces a strong electric field in the neutral co-moving frame which leads to plasma heating at some parts of the disk [2]. In 2015, Okuzumi and Inutsuka reported that this plasma heating reduces the electric conductivity J/E before the onset of impact ionization. Also, the influence of the plasma heating on ionisation degree of the gas results the Ohm's law to be nonlinear in  [3]. It has been observed that this plasma heating triggered by the electric field eventually leads to an asymmetric electron distribution in the protoplanetary disk, which can be represented by the Davydov distribution function [4]. In this paper, we investigate how this asymmetry in electron distribution plays a significant role in the behaviour of electrostatic solitary waves (ESW) that are produced in the PPD. In Section II, we give a brief description of MRI turbulence and the resultant plasma heating in the disk as well as electron heating in a PPD. In Section III, we put forward our basic formalism of the Sagdeev potential. Finally in Section IV, we summarise the work. II. MRI turbulence and plasma heating Consider a weakly ionised plasma with an abundance of neutrals. In absence of any accelerating field, the electrons tend to thermalize with the neutrals. However, when there is an external electric field, electrons are accelerated heavily due to their mobility and low energy transfer during binary collisions. So, there exists an equilibrium in such a plasma, where the external electric field  ≫  !"#$ such that the random thermal energy of the electrons greatly exceeds that of the neutrals, namely  !!! ≫ √  !  ! , where the `n' subscript denotes the neutrals, and 46 th EPS Conference on Plasma Physics P5.4009