Inducing Microbunching in the CLARA FEL Test Facility

We present simulation studies of the laser heater interaction in the CLARA FEL test facility using a non-uniform laser pulse. The microbunching instability, which manifests itself as correlated energy or density modulations in an electron bunch, can degrade the performance of an FEL. Most x-ray free electron lasers (FELs) utilise a so-called laser heater system to impose a small increase in the uncorrelated energy spread of the bunch at low energy to damp the instability – this technique involves imposing a laser pulse on the bunch while it is propagating through an undulator in a dispersive region. However, if the instability can be controlled, the electron bunch profile can be manipulated, yielding novel applications for the FEL, or for generation of THz radiation. Control of the microbunching instability can be achieved by modulating the intensity profile of the laser heater pulse to impose a non-uniform kick along the electron bunch. We have simulated this interaction for various laser intensity profiles and bunch compression factors.
Proceedings of the 38th Int. Free Electron Laser Conf., FEL2017, Santa Fe, NM, USA