A Study for Beam Dynamics of the Korea Fourth Generation Storage Ring

Abstract

본문에서 저장링 내에서의 선형 동역학과 비선형 동역학에 대한 설명을 포함하여 Korea-4GSR의 격자 구조는 기술된다. 에미턴스를 줄이기 위해서 MBA 격자 개념이 적용되고, longitudinal gradient bending magnet과 reverse bending magnet이 이용된다. 비선형 효과는 육극자석을 최적화하여 통제한다. 최적화 결과는 resonance driving term이 잘 상쇄되는 것을 보여준다. Korea-4GSR에서의 IBS 효과도 조사하였다. IBS에 의한 에미턴스 증가는 평평한 빔일 때 14 %, 둥근 빔일 때 5%이다. IBS와 연관된 Touschek lifetime은 빔 lifetime에 가장 결정적인 영향을 미치고 lifetime은 평평한 빔일 때 4.54 시간, 둥근 빔일 때 8.81 시간이다. 디자인이 현실적인지 확인하기 위해서 에러 보정 전산모사 그리고 입사 전산모사를 수행했다. 전산모사에서 에러들은 잘 보정되었고 입사 효율은 약간의 입사빔 에너지 편차가 있을 때 100 %였다. 종합해보면 Korea-4GSR 격자 디자인은 작은 자연에미턴스를 만든다. 이때, IBS 효과에 의한 에미턴스 증가는 작고 lifetime 또한 빔 운전하기에 충분히 길다. 그리고 그 디자인의 현실성은 전산모사를 통해 확인하였다.

In this dissertation, we present a newly designed magnetic lattice of the Korea fourth-generation storage ring (Korea-4GSR) and results of linear and non-linear beam dynamics studies. This storage ring employs the multi-bend achromat (MBA) structure to achieve very small natural emittance of an electron beam. The designed natural emittance is 58 pm, the electron-beam energy is 4 GeV, and the ring circumference is approximately 800 m. To realize a very small emittance, longitudinal gradient bending magnets together with reverse bending magnets are introduced, both of which led the emittance reduction down to two orders of magnitude smaller than that in existing third-generation storage rings. Damping wiggler option is also studied to explore the possibility of further reduction of the emittance, and it is found that the natural emittance can be reduced to 34 pm. Harmful non-linear effects are controlled by optimizing the distribution and strength of sextupoles. Then resonance driving terms are obtained and analyzed to examine their impact on nonlinear dynamics. This study is validated by considering on- and off-momentum dynamic apertures. It is found that the resulting dynamic apertures are large compared to those in other 4GSRs. Effect of the Intrabeam scattering (IBS) on the beam emittance is investigated and it is confirmed that the chosen electronbeam energy and the natural emittance are close to optimal considering the emittance increase due to IBS. Tolerance for various magnetic errors including those that lead to closed-orbit distortion and magnetic multipole errors are investigated, and orbitcorrection scheme is also described. Finally, a method for injection into the storage ring is presented and it is confirmed that due to large dynamic aperture the conventional off-axis injection is feasible for the Korea-4GSR.