PRECISE RF CONTROL SYSTEM OF THE SCSS TEST ACCELERATOR

We present the development and performance of the low-level rf control system of the SCSS test accelerator. The rf phase and amplitude of the acceleration field are precisely controlled by a low-level rf system comprised of IQ modulators / demodulators and VME waveform generators / digitizers. Recent improvements established high-resolution phase and amplitude setting capabilities of 0.01 degree and 0.01%, respectively. In addition, the phase disturbance due to the temperature drift of an acceleration cavity was reduced by tuning a precise temperature regulation system. The temperature fluctuation was improved to be 0.01 K rms. As a result, the rf phase and amplitude stabilities of sub-harmonic buncher cavities were achieved to be 0.02 degree rms and 0.03 % rms, respectively. The saturated FEL radiation in the wavelength region of 50–60 nm is stably generated