J-PARC RCS; High-order field components inherent in the injection bump magnets and their effects on the circulating beam during multi-turn injection

J-PARC RCS; 入射バンプ電磁石に内在する高次磁場成分が多重入射中のビームに及ぼす影響

發知 英明  ; 原田 寛之  ; 高柳 智弘   

Hotchi, Hideaki; Harada, Hiroyuki; Takayanagi, Tomohiro

In the J-PARC RCS, we investigated the influences of high-order field components inherent in four sets of injection bump magnets (dipole magnets) on the circulating beam during multi-turn injection. Ideally, the injection bump fields including the high-order field components are cancelled out with each other through the integration over the four injection bump magnets. But, in the RCS, such a field compensation is incomplete owing to the effects of magnetic interferences and feed-down fields. The residual high-order field components, not cancelled out, have a significant influence on the circulating beam via the excitation of high-order random betatron resonance. In this paper, we discuss the detailed mechanism of emittance growth and beam loss caused by the high-order field components of the injection bump magnets including their correction scenario, on the basis of numerical simulation and experimental results.