Comparison between measurements and ORBIT code simulations for beam instabilities due to kicker impedance in the 3-GeV RCS of J-PARC

Saha, P. K.   ; Shobuda, Yoshihiro   ; Hotchi, Hideaki  ; Harada, Hiroyuki  ; Hayashi, Naoki  ; Tamura, Fumihiko   ; Yamamoto, Masanobu   

Transverse impedance of the extraction kicker magnets is the most dominant beam instability source in the 3-GeV RCS of J-PARC. We made a significant upgrade of the ORBIT code for beam simulations in synchrotrons like J-PARC RCS including a successful implementation of the time dependent impedance in the code. Simulation results are found to quite good in agreement with measurements done for a beam power up to 500 KW. Beam instability occurs when AC chromatic correction is done but no beam instability occurs for a DC chromatic correction. Simulation results for the designed 1 MW shows that instability occurs even for a DC chromatic correction when betatron tunes are kept fixed throughout the acceleration process. It is thus a big concern towards 1 MW goal but simulation also shows that a proper tune manipulation can stabilize the beam. The simulation thus suggests that necessary steps should be taken in order reduce kicker impedance although a proper beam tuning remains as an alternate option.