Phase Stability in the RF Reference System for the PEFP 100-MeV LLRF Control System

Phase Stability in the RF Reference System for the PEFP 100-MeV LLRF Control System

The 100-MeV proton linear accelerator of the Proton Engineering Frontier Project (PEFP) has been developed and consists of a 3-MeV radio frequency quadrupole accelerator (RFQ), a 20-MeV drift tube linac (DTL), a medium energy beam transmitter (MEBT), and 100-MeV DTL tanks. The error of the accelerating field in the cavity should be within ±1° in phase and ±1% in amplitude,and the phase difference between adjacent cavities should be maintained continuously. To satisfy these requirements, high phase stability is required in the RF reference system for the PEFP lowlevel radio frequency (LLRF) control system. The RF reference system for the PEFP 100-MeV accelerator, which is composed of a local oscillator (LO), a rigid coaxial reference line of about 80-m length, Heliax cables, and LLRF analog components, was designed and its phase stability was evaluated. The reference signal was chosen to be the 300 MHz LO signal for phase stability of the LLRF control system. The phase noise of the local oscillator was measured and calculated as a phase error of 0.058 degrees. In the entire length of the RF reference distribution line, a phase stability of ±0.05 degrees was evaluated for a temperature change of ±0.1 °C. The phase stability of the LLRF analog system for up/down-conversion was also measured and depended on the temperature stabilization.

The 100-MeV proton linear accelerator of the Proton Engineering Frontier Project (PEFP) has been developed and consists of a 3-MeV radio frequency quadrupole accelerator (RFQ), a 20-MeV drift tube linac (DTL), a medium energy beam transmitter (MEBT), and 100-MeV DTL tanks. The error of the accelerating field in the cavity should be within ±1° in phase and ±1% in amplitude,and the phase difference between adjacent cavities should be maintained continuously. To satisfy these requirements, high phase stability is required in the RF reference system for the PEFP lowlevel radio frequency (LLRF) control system. The RF reference system for the PEFP 100-MeV accelerator, which is composed of a local oscillator (LO), a rigid coaxial reference line of about 80-m length, Heliax cables, and LLRF analog components, was designed and its phase stability was evaluated. The reference signal was chosen to be the 300 MHz LO signal for phase stability of the LLRF control system. The phase noise of the local oscillator was measured and calculated as a phase error of 0.058 degrees. In the entire length of the RF reference distribution line, a phase stability of ±0.05 degrees was evaluated for a temperature change of ±0.1 °C. The phase stability of the LLRF analog system for up/down-conversion was also measured and depended on the temperature stabilization.