Study of operation above half-integer random resonance in the J-PARC RCS

Kojima, Kunihiro ; Harada, Hiroyuki  ; Okabe, Kota  ; Chimura, Motoki   ; Saha, P. K.   

In the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, the beam power ramp-up aiming to surpass the design of 1 MW enhances the space charge effect and pushes the beam toward the structure resonance. To mitigate the beam loss, the operating point is required to be apart from the structure resonance corresponding to the beam power ramp-up, although any changes in the operating point lead to an increase in the beam loss due to the approach to other resonances. We recently compensated the horizontal half-integer resonance located just above the current operating point to address this issue, and we are now ready to explore a higher tune region than that. We confirmed in a tune survey that the vertical half-integer and linear sum resonances are substantially excited. In addition, the linear sum resonance is found to be well compensated by making a vertical local bump in the arc section.