Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators

In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms– Free Electron Laser (FEL) and Inverse Free Electron Laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2laser lines, electrons can be microbunched with different periodicity 300 –100 μm suitable for injection into plasma densities in the range 10¹⁶– 10¹⁷cm^-3, respectively. The requirements on the THz radiation power and the electron beam qualities are also discussed.