Commissioning of a New X-Band, Low-Noise LLRF System

To increase beam energy in the CLEAR facility at CERN and study the CLIC accelerating structure prototype in operating conditions, the first X-band test facility at CERN was upgraded in 2020. Both, the acquisition and software systems at X-band test stand 1 (Xbox1) were upgraded to exhibit low phase noise which is relevant to klystron based CLIC and to the use of crab cavities in the beam delivery system. The new LLRF uses down-conversion which necessitates a local oscillator which can be produced by two different methods. The first is a PLL, a commonly used technique which has been previously employed at the other X-band facilities at CERN. The second is a novel application of a single sideband up-convertor. The up-convertor system has demonstrated reduced phase noise when compared with the PLL. The commissioning of the new system began in late 2020 with the conditioning of a 50 MW Klystron. Measurements of the quality of the new LLRF will be shown. These will compare the PLL and up-convertor with particular attention on the quality of the phase measurements. Also, a preliminary study of phase shifts in the waveguide network due to temperature changes will be presented.
Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil