High brightness and high average power Free Electron Lasers known as x-ray FELs, developed by DOE, are intently desired by the scientific community for their unique capabilities and for the opportunities they enable in the medical and biological sciences, such as imaging biological molecules or chemical reactions. Beam optics codes (particularly Particle-in-Cell codes) couple non-uniformity and surface structure to current and emittance in a complex manner and are the de facto tool of choice in device design, but such codes neglect time-dependent contributions to the emission current due to the difficulty of accounting for multiple scattering events on the emission distribution. Such a limitation
