Abstract
For the acceleration of very high intensity protons in the 3 GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), the beam loading compensation in the rf accelerating cavities is implemented. The magnetic-alloy (MA) loaded cavities, which have a wide-band frequency response, are employed in the J-PARC RCS. The wake voltage in the wide-band MA cavity consists of not only a component of the fundamental accelerating rf, but also the higher harmonics. We developed a multiharmonic feedforward compensation system, which handles the most important three harmonics ($h=2,4,6$). The function of the multiharmonic feedforward is described. Adjustments of the amplitude and phase patterns for the cancellation of the wake voltage during the acceleration period are not trivial. We developed the commissioning methodology of the feedforward. We describe the methodology in the cases without and with driving the accelerating rf. The commissioning of the systems for 11 cavities in the RCS was successful. We describe the commissioning results and the beneficial effects of the feedforward compensation in the beam operation.
Highlights
In the 3 GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) [1,2,3]. the magnetic-alloy (MA) loaded cavities are employed to generate the high accelerating voltage, which is necessary to accelerate high intensity proton beams
In the barrier cavity in the Brookhaven AGS, which has a very low Q value about 0.6, a multiharmonic FF system was used [14]. It is reported in the references above that the multiharmonic beam loading compensation by the rf feedforward method works; the compensation was performed without driving rf voltages and frequency sweeps, which is necessary for the application to the J-PARC RCS
One can notice that the third harmonic (h 1⁄4 6) component appears in the cavity voltage monitor from 0 to 15 ms while in the level rf (LLRF) driving rf only the fundamental (h 1⁄4 2) and the second harmonic (h 1⁄4 4) components exist
Summary
In the 3 GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) [1,2,3]. the magnetic-alloy (MA) loaded cavities are employed to generate the high accelerating voltage, which is necessary to accelerate high intensity proton beams. We employ the rf feedforward (FF) method to compensate the multiharmonic beam loading. The multiharmonic beam loading compensation in a wide-band MA cavity by the feedforward method was tested by using electron beams [13]. In the barrier cavity in the Brookhaven AGS, which has a very low Q value about 0.6, a multiharmonic FF system was used [14] It is reported in the references above that the multiharmonic beam loading compensation by the rf feedforward method works; the compensation was performed without driving rf voltages and frequency sweeps, which is necessary for the application to the J-PARC RCS. It is not easy to adjust the feedforward parameters during a full acceleration period, in which the parameters such as frequencies and relative loading factors Y vary, by analog circuits. We describe the details of the methodology and present the commissioning results
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