Effects of ambipolar potential on multiple mirror confinement

The diffusion model for multiple mirror confinement has previously been limited to devices with a large number of cells and high mirror ratios. Ambipolar effects were assumed to reduce the confinement time by the usual factor [1+Z(T/sub e/ /T/sub i/)]-1. For the ideal multiple mirror regime, in which the mean free path is shorter than the cell length but long compared with the mirror scale length, a new discrete staircase density profile model, without those limitations, has been developed. A theory employing model distribution functions for ion and electron transport in a multiple mirror device has been used. A self-consistent ambipolar potential is included. It has been found that the ambipolar potential reduces the confinement time somewhat less than the usual ambipolar factor. Special attention is given to the last cell which acts as a boundary condition for the system. The ambipolar potential across the last mirror throat is studied and found to be of the order of 0.3kT/sub e/. For devices with small numbers of cells, significant improvements over previously calculated multiple mirror confinement times are found