During the past two years computer simulation has been used extensively to obtain a detailed description of pulse trapping and pulse stacking of relativisticElayers in astron. Resistors are essential to good trapping, in agreement with experiment. In the code, pulse trapping can easily be arranged to be 100% efficient—in marked contrast to the experiment. Details of pulse stacking are dependent on resistor configuration, degree of charge neutralization, and external well shape, but the field reversal increase invariably runs into a saturation due to axial expansion of the layer. This process can be described as a phase space exclusion or, alternatively, as nonadiabatic axial heating. The pulse‐stacking process involves a tearing and bunching, and it is also nonadiabatic in the radial motion; as a consequence, radial expansion always occurs, and this can also act as a limitation to field reversal unless the resistor locations allow considerable radial room. Very tightly focused (axially) pulses can result from vacuum pulse trapping if system conditions are optimized correctly. This in turn lessens the axial expansion problem for vacuum layers. In contrast, the radial expansion problem is much more severe for vacuum layers, and this effect causes radial loss at some layer strength well short of field reversal. Large‐current (2500 A) nuetralized pulses result in field reversal with one pulse.