A time-dependent, two-dimensional, axisymmetric magnetohydrodynamics code is employed to model, validate and extend the experimentally-limited performance characteristics of a GigaWatt-level plasma source that utilized magnetoplasmadynamic acceleration for gas energy deposition. Accurate modeling required an upgrade of the code's circuit routines to properly capture the Pulse-Forming-Network current waveform which also serves as the primary variable for validation. Comparisons to experimentally deduced current waveforms were in good agreement for all power levels. The simulations also produced values for the plasma voltage which were compared to the measured voltage across the electrodes. Trend agreement was encouraging while the magnitude of the discrepancy is approximately constant and interpreted as a representation of electrode fall voltage. Force computations captured the expected electromagnetic acceleration trends and serve as further verification. They also allow examination of the device as a very-high power magnetoplasmadynamic thruster operating at power levels in the excess of 180M W. The computations offer insights into the plasma's characteristics at different power levels through two-dimensional distributions of pertinent parameters and identify design guidelines for effective stagnation temperature values as a function of mass-flow rate.