Coherent synchrotron radiation monitor for microbunching instability in XFEL

The microbunching instability is an important issue in an X-ray Free Electron Laser (XFEL). The intensity of the Free Electron Laser (FEL) can be reduced significantly by the microbunching instability so that the laser heater is widely used to reduce it. In the X-ray Free Electron Laser of the Pohang Accelerator Laboratory (PAL-XFEL), to directly monitor the microbunching instability, a visible charge coupled device camera was included into the coherent radiation monitor which uses a pyroelectric detector. It enabled us to measure the microbunching instability more clearly and optimize the FEL lasing in the PAL-XFEL.