Improvements to PARMILA

PARMILA is an internationally accepted standard for Monte Carlo simulation of linac and transport line performance. We discuss several modifications and improvements to this code. A generalized magnet routine allows the simulation of electrostatic and magnetic quadrupoles, solenoids, sextupoles, and octupoles. Optional inclusion of linear fringe fields and/or geometric aberrations is provided for in the quadrupole transformation. The dipole routine has been replaced with a more accurate algorithm. The accelerating gap transformation has been replaced by a set of implicit equations which accurately describe the relativistic particle behavior in the presence of longitudinal and transverse electric fields described by a set of 6 weighted Fourier moments (transit time factors). A simple model allows these moments, in turn, to be approximated from the cell geometry and the usual T and S functions. A number of added convenience features - interactive disk storage and retrieval of particle coordinates, individual particle input and observations, an interactively callable test for particle longitudinal stability, and an automated quadrupole tuning procedure - all add to the code's versatility, convenience, and strength as a design tool.