Hybrid Accelerator Design for a Free Electron Laser

An accelerator system for a free electron laser (FEL) is described that incorporates both an electrostatic accelerator and an RF linac. The purpose of the design is to minimize the emittance of the high current pulses injected into the RF linac. Emittance contributes to the effective energy spread of the beam in the FEL. A large effective energy spread will reduce gain and conversion efficiency. The pulses leaving the electrostatic accelerator are compressed in a dispersive magnetic buncher before injection into the linac. After the beam leaves the FEL, energy is recovered in an RF decelerator followed by a decelerating and collecting column in the electrostatic accelerator. A new electrostatic accelerator design is presented to both provide high charging current and collect an electron beam with a large fractional energy spread.