The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) is now in the final beam commissioning phase, aiming for a design output beam power of 1 MW. With a series of injector linac upgrades in 2013 and 2014, RCS developed a high-intensity beam test, and launched 1-MW beam tuning in October 2014. The most important issues in realizing such a high-power continuous beam operation are to control and minimize beam loss for maintaining machine activations within permissible levels. In RCS, numerical simulation was successfully utilized along with experimental approaches to isolate the mechanism of beam loss and find its solution. By iteratively performing actual beam experiments and numerical simulations, and also by several hardware improvements, we have recently established a 1-MW beam operation with very low fractional beam loss of a couple of 10 −3 . In this paper, our recent efforts toward realizing such a low-loss high-intensity beam acceleration are presented as a follow-up of our previous article, H. Hotchi et al. Phys. Rev. ST Accel. Beams 12, 040402 (2009), in which the initial beam commissioning status of RCS has been reported.
The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex was commissioned in October 2007. Via the initial beam tuning and a series of underlying beam studies with low-intensity beams, since December 2009, we have intermittently been performing beam tuning experiments with higher-intensity beams including the injection painting technique. By optimizing the injection painting parameters, we have successfully achieved a 420 kW-equivalent output intensity at a low-level intensity loss of less than 1%. Also the corresponding numerical simulation well reproduced the observed painting parameter dependence on the beam loss, and captured a characteristic behavior of the high-intensity beam in the injection painting process. In this paper, we present the experimental results obtained in the course of the RCS beam power ramp-up, especially on the beam loss reduction achieved by employing the injection painting, together with the numerical simulation results.
The 3 GeV rapid-cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) project generates a 1 MW proton beam. In operation of a high intensity hadron accelerator, the most important issue is to minimize the uncontrolled loss. The RCS beam collimation system is designed for this purpose and the performance is confirmed. In the present design, the physical aperture is 1.5 times wider than the primary collimator aperture, so that the beam loss can be sufficiently localized under this condition. The influence of positioning errors of the collimators is also estimated. Furthermore, the dependence of the collimation efficiency on the impact parameter is investigated taking the growth process of the beam halo into consideration. As a result, the beam loss mechanism changes according to the impact parameter.
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