Rapid 3-D Simulation of a Bunch-Length Diagnostic for Laser Wakefield Accelerators via Coherent Transition Radiation at THz Frequencies

76105-Laser wakefield accelerator (LWFA) concepts, characterized by ultra-high gradients and ultra-short bunch lengths, show great promise for reducing the cost and size of future high-energy electron linacs. A new non-invasive, bunch-length diagnostic is critical to continuing the rapid advances in LWFA technology. Coherent transition radiation (CTR), generated as the short bunches exit the plasma, could provide such a diagnostic if the effects of various secondary complications were quantified. This project will develop particle-in-cell (PIC) simulations to characterize the CTR emitted from a self-modulated (SM) LWFA. In Phase I, methods for maximizing the emitted energy at the THz frequencies will be explored. Simulation results will be used to interpret experimental data. High-risk technical issues will be resolved by showing that explicit two-dimensional Cartesian PIC simulations can correctly model a full SM-LWFA interaction, including the CTR emission from the micron-scale electron bunches emerging from plasmas. Also, a new ponderomotive guiding center treatment of the laser pulse will be implemented within the framework of the existing PIC code. Commercial Applications and Other Benefits as described by the awardee: The enhanced PIC simulation code should provide a uniquely powerful bunch-length diagnostic for plasma-based accelerators. In addition, a new and uniquely powerful source of THz radiation could have many applications in medicine, science, and national security.