Transition from Pastukhov to collisional confinement in a magnetic and electrostatic well

It is shown that the Pastukhov formula for charged particle confinement in a combined magnetic and electrostatic well becomes invalid when the mean free path, reduced by the mirror ratio, is of the order of the system length. A smooth transition is made to a collisional confinement time based on a completely filled loss cone which gets depleted only at the end of the system. A Monte Carlo computer code is used to study the transition regime, and it shows that a good model is to add the analytic Pastukhov and collisional confinement times.