TDA3D: Updates and improvements to the widely used three-dimensional free electron laser simulation

TDA3D is a widely distributed and often used Free Electron Laser (FEL) simuIation code. While a number of versions of TDA exist, this paper describes the official version which is well tested and supported. We describe the capabilities of the code emphasizing recent improvements and revisions. TDA3D is a steady-state (time-independent) amplifier code. The code self-consistently solves, after averaging over a wiggler period, the paraxial wave equation for the radiation field and the Lorentz equations of motion for the electrons. The paraxial wave equation includes diffraction and optical guiding. The calculation of the electron beam motion takes into account longitudinal bunching and transverse betatron oscillations, so that emittance, energy spread, and external focusing can be properly modeled. Recent additions to the simulation include the ability to model natural wiggler focusing in one or both planes, alternating gradient quadrupoles or sextupoles, and ion channels. The initial loading of the electron distribution can be controlled to allow for matching into focusing channels, improved quiet starts (non-correlated phase-space distributions), and arbitrary energy spread.