Beam instability suppression in the 3-GeV RCS of J-PARC

In the 3-GeV Rapid Cycling Synchrotron (RCS) of Japan Proton Accelerator Research Complex, significant beam instability is caused by the transverse impedance of the extraction kicker magnets. The hardware measures to reduce the kicker impedance are in progress slowly, which needs extensive R and D studies for practical implementation. In order to study a detail beam instability nature we used ORBIT code by successfully introducing all realistic time dependent machine parameters including the impedance. We studied a detail of the parameter dependence such as the degree of chromaticity correction, choice of betatron tunes as well as momentum spread of the injected beam in order to determine realistic parameters to suppress the beam instability at 1 MW. The simulation results are well reproduced in the measurements, while an acceleration of 1 MW beam has also been successfully accomplished. The beam instability scenarios at high intensities and measures to accomplish 1 MW beam acceleration based on the simulation and experimental studies are presented in this paper. (author)