PBGUNS is a fully interactive program for the simulation of axisymmetric and 2D electron and ion beams.  A plotting package is employed so that high resolution plots can be viewed on the interactive screen and quality output hard copy plots are available. Cycle-by-cycle results (trajectories, equipotentials, emittance, cathode current densities, and exit plane current distributions) are displayed on the screen while the program is running. Input is fully interactive and only modest knowledge of the input data set is needed. The program can be interrupted and changes can be made to the electrodes or parameters at any time and it is quite tolerant of significant changes being made to the problem.

PBGUNS can simulate virtually any thermionic or field emission, electron gun or beam; or positive or negative, plasma, thermionic or sputter source, ion gun or beam. It can be applied to nanometer-sized, 100 Volt, micro-field emitters and to MeV electron devices and guns. The calculations can be fully relativistic, including self-induced as well as applied magnetic fields. The cathode can be thermionic, employing a Child's Law current density computation (with Langmuir-Blodgett corrections) or it can be a field emitter obeying the Fowler-Nordheim emission law. Ions can be extracted from plasmas, plasma sputter sources, beam sputter sources or thermionic surfaces. PBGUNS will determine the plasma boundary for plasma (positive or negative ions) sources and does not require a "curvature" or any other knowledge of the beam or plasma.

PBGUNS solves Poisson's Equation using iterative relaxation techniques (in double precision, 64 bit arithmetic) on a rectangular array of squares, with an up to 20 times finer mesh (for greater accuracy and stability) covering the cathode or plasma region. The rectangular array of squares makes the calculations of space charge easier and more precise with the ultimate result that the program is very accurate, especially in the critical region near the cathode or ion emission-extraction surface. The program automatically determines the plasma surface for ion beam extraction from a plasma. Space-charge densities are computed from representative trajectories, each carrying current assigned at injection, through the device. Electrode line segments are quadratic equations, usually straight lines or circles. The beam can be saved and restarted on a new mesh for long beam lines. Execution times (on a Pentium PC) can vary from as little as 2 minutes for the smallest arrays to an hour for very large arrays.