A self-consistent beam loaded traveling wave accelerator model for use in TRACE 3-D

An optics model of a constant gradient traveling wave (CGTW) accelerator structure has been implemented for TRACE 3-D. TRACE 3-D is an envelope code including space charge that is used to model bunched beams in magnetic transport systems and radio frequency (RF) accelerators when the effects of beam current might be significant. The new matrix model has been developed to allow incorporation of particle beam loading (current) effects on the accelerator gradient and the accelerator structure's beam focusing properties in a self-consistent manner. The beam loaded electric field for a CGTW accelerator structure is constant for only a particular design current (e.g. 0 current), otherwise it can be written as a function of accelerator attenuation and axial position along the structure. The variation of the electric field through the structure has been taken into account in the new model. CGTW structures differ substantially in focusing properties and beam loading properties from standing wave structures. Examples are presented using the new TW model, propagating electron beams with different currents through the Stanford Linear Accelerator Center's 3 m structure. The results will be compared to the zero current TW structure model in TRANSPORT and the Tank model (a standing wave structure model) in TRACE 3-D. A computer demonstration of the new element is also presented.