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

Shen, G.; Ikegami, Masanori*

In the beam commissioning of J-PARC linac, the RF set-point tuning has been performed based on a phase scan method. In the tuning of DTL2 and DTL3, the phase scan curves show a remarkable agreement with the numerical model. In the DTL1 tuning, however, the phase scan curves show a notable discrepancy from the numerical model especially with the RF set-points far from its design value. A three-dimensional particle simulation has been conducted with IMPACT, and the generation of the low energy component and the severe filamentation are identified as the main sources of the observed discrepancy. To circumvent this difficulty, we have adopted two phase scan curves as the reference restricting the parameter range for the phase scan. The reference curves and scanning phase range are carefully determined to avoid the influence from the filamentation. The tuning goal of 1 in phase and 1% in amplitude is satisfied for DTL1 with the two-reference scheme.