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

The J-PARC linac has three DTL tanks to accelerate the negative hydrogen ions front 3 to 50 MeV. The phase and amplitude are adjusted for each cavity with a phase scan method within the accuracy of 1 degrees in phase and 1% in amplitude. The experimental results show, a remarkable agreement with the numerical model within a sufficient margin in the tuning of the last two DTL tanks. However, a notable discrepancy between the experiment and the numerical model is seen in the tuning of the first DTL tank. After studying with a three-dimensional multi-particle simulation, the generation of the low energy component and the pronounced filamentation are identified as the main causes of the discrepancy. The optimization of the tuning scheme is also discussed to attain the tuning goal accuracy for the first DTL tank.