Abstract
Equipartitioning is an efficient beam-dynamics design scheme also for radio frequency quadrupole (RFQ). To realize an equipartitioned RFQ, it is essential to reproduce the nonuniform intervane voltage profile required from the beam dynamics. We developed a cavity design and tuning method to this end. The dimensions of a voltage-ramped four-vane cavity were determined by a three-dimensional rf simulation. To produce the desired vane voltage profile, the longitudinal variation of the cross-sectional shape was adjusted using the least-squares method based on the simulated responses of the vane-base width to the quadrupole-mode field. In the low-level tuning, slug-tuner positions were determined based also on the least-squares solutions obtained from the simulated tuner responses to the field profile. Finally, the deviation of the quadrupole-mode field was within 1.5% from the design profile, and the mixed dipole modes were 1% of the quadrupole-mode field after only two iterations of tuner adjustment; they are sufficiently smaller than the requirement of 2%.
Highlights
In recent high-intensity hadron accelerators, excessive beam loss is a potential cause of radio activation on the accelerator components
To satisfy the beam-quality requirements with an optimized length, we developed and demonstrated an radio frequency quadrupole (RFQ) for the Japan Proton Accelerator Research Complex (J-PARC) [1] H− linac based on the beam-oriented design scheme [2]
The equipartitioning beam-dynamics design is implemented to this RFQ, so this RFQ is called epRFQ
Summary
In recent high-intensity hadron accelerators, excessive beam loss is a potential cause of radio activation on the accelerator components. The analytical method is good for understanding the principle; the parameters, such as the resonant frequencies of each mode, should be carefully calculated to obtain a proper response function Sometimes, it is difficult, or the model becomes too complicated, to derive the response function if detailed structures such as dipole stabilizing rods (DSRs) on the cavity ends [8,9] are implemented. We established a method to realize the ramped V profile required from the equipartitioning beam-dynamics design by making full use of the FEM tool. This significantly simplifies the tuning procedure and shortens the tuning time. We describe in detail the procedure for this rf design and tuning method developed for epRFQ
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