“…The first of the these problems leads to solution of Laplace or Poisson's equation, and the second one to solution of transport equation defined for the phenomena taking place in the IMS detectors as, so called, advection-diffusion problem [15]. In case of analysis of phenomena occurring in vicinity of the collector electrode, the solution of the non-stationary problems is essential, because the final goal is to find time dependence of current flowing from the collector.…”