Tuning of RF amplitude and phase for the separate-type drift tube linac in J-PARC

It is important to accurately adjust the amplitude and the phase of RF power sources for a high intensity proton linac. J-PARC (Japan proton accelerator research complex) linac is one of those high-intensity linacs. J-PARC linac has 30 SDTL (separate-type drift tube linac) tanks to accelerate the negative hydrogen ions from 50 to 181 MeV. Two neighboring SDTL tanks are driven by one klystron, where the phase and the amplitude of these two tanks are controlled in terms of the vector sum. The target-value of the vector sum control should be determined with a beam-based tuning for each klystron. During the beam commissioning, the RF tuning has been performed with a phase scan method introducing a concept of phase signature matching. In the tuning, the output beam energy from the SDTL module is monitored while scanning the RF phase. Comparing the obtained phase dependence of the output beam energy with those from a numerical model, the target-values for the low-level RF control system has been tuned within the required accuracy of 1° in phase and 1% in amplitude. The same tuning procedure has successfully been applied to the RF tuning of buncher and debuncher cavities.