May question is about possible approaches to solve the following system $$ \begin{array}{rcl} \nabla{n}&=&n\,\mathbf{E},\\ \nabla\cdot\mathbf{E}&=&1-n, \end{array} $$ in general with some boundary conditions (BC). In particular, I'm interested to solve it in the polar coordinates $$ \begin{array}{rcl} \partial_rn&=&nE_r,\\ \partial_{\varphi}n&=&rnE_{\varphi},\\ \partial_r{(rE_r)}+\partial_{\varphi}{(E_{\varphi})}&=&r(1-n), \end{array} $$ plus some BC.
Any suggestions?
Update 1
According to request of @nicoguarolet let's say that boundary conditions are as follows $$ \begin{array}{c} \left.n(r,\varphi)\right|_{r=r_L}=n_0\approx1,~ \left.E_{\varphi}\equiv E_r(r,\varphi)\right|_{r=r_L}=E_0\approx0,\\ \left.\partial_rE(r,\varphi)\right|_{r=r_R}=0,\\ \end{array} $$ where $[r,\,\varphi]\in[r_L,\,r_R]\times[\varphi_L,\,\varphi_R].$ Hope, that I haven't missed somewhat.