  A 2D nonlinear model for the electrical potential in the edge plasma in a
tokamak generates a stiff problem due to the low resistivity in the direction
parallel to the magnetic field lines. An asymptotic-preserving method based on
a micro-macro decomposition is studied in order to have a well-posed problem,
even when the parallel resistivity goes to $0$. Numerical tests with a finite
difference scheme show a bounded condition number for the linearised discrete
problem solved at each time step, which confirms the theoretical analysis on
the continuous problem.
