\begin{thebibliography}{9}

\bibitem{bmad}
    D. Sagan, ``Bmad Manual'' https://www.classe.cornell.edu/bmad/manual.html, section 14.3  pp. 254-256.
\bibitem{mcmillan}
E. M. McMillan,``Multipoles in Cylindrical Coordinates,” Nucl. Instrum. Meth. 127, 471 (1975)
\bibitem{wanwei}
W. Wu, ``The 3D electric field map from OPERA-3D'', E989 Note 117: docdb 8162-v1, 6 Sept. 2017
\end{thebibliography}
