Achievement of a low-loss 1-MW beam operation in the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

Abstract

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.

Empirical condition of betatron resonances with space charge

“…The widest one is located just below the bare tunes of 6.5. After a careful tune survey, the operating point of the RCS has been chosen at around ðν 0x ; ν 0y Þ ¼ ð6.45; 6.42Þ [63], which is consistent with the theoretical prediction in Fig. 19.…”

“…The thin solid lines show the positions of the resonances at zero-intensity limit (η → 1). A red dot on the picture indicates the typical operating point of the RCS, i.e., ðν 0x ; ν 0y Þ ¼ ð6.45; 6.42Þ [63]. the right-hand side can give rise to a lot of extra instability bands overlooked or underestimated in previous resonance studies.…”

“…As shown in Fig. 19, a clear third-order difference resonance band is lying near the regular operating point of the RCS [63,70]. Since the sophisticated injection painting scheme is available in this high-power machine, the ratio of the initial transverse emittances can be controlled over a wide range.…”

“…Let us try to draw a stability tune diagram for a particular machine, applying the general rule described above. As an example, we consider the lattice of the rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) [63]. So far, the spacecharge-induced resonance in the RCS has been discussed on the basis of the incoherent tune spread as in Fig.…”

Rapid-cycling synchrotron for multi-megawatt proton facility at Fermilab

“…The J-PARC RCS has demonstrated successful operation with a Laslett tune-shift of 0.3 and a corresponding tune-shift per superperiod of 0.1 [10]. We propose to operate the Fermilab RCS with the higher tune-shift of 0.35, but a smaller tune-shift per superperiod of 0.044 .…”