Close-loop control system of the optical klystron magnetic gap of CHG-SRFEL

This paper gives a description of the principle of the magnetic gap control system of the optical klystron for the coherent harmonic generation storage-ring free-electron laser (CHG-SRFEL) in the National Synchrotron Radiation Laboratory. The hardware construction and software flowchart are illustrated for reliably engineering implementation of the system. The magnetic gaps of the three parts of optical klystron, including modulator, dispersive section and radiator can be adjusted separately or simultaneously, and the resolution, can reach 20 μm with the precision of 5 μm. By means of optimizing the position monitoring instrument of the system, the resolution and the precision can be improved to 1.0 μm and 0.2 μm respectively. The vacuum chamber of the storage ring between the optical klystron is free of destruction by multi-protection system. Such system has been employed in the measuring and shimming of the optical klystron magnetic field.