Abstract
General optimization procedure, computation methods used, and the obtained optimal parameters of undulators for the NSLS‐II project beamlines are reported. The optimization starts with high‐accuracy calculation of undulator magnetic fields, using Radia magnetostatics code, for a large set of periods and vertical gaps of a given undulator type, given magnetic materials and a scalable magnet geometry. From the resulting magnetic fields, a sub‐set of undulator periods and the corresponding vertical gaps, providing the required low‐energy cut‐off values of spectral harmonics for each particular beamline, is determined. In parallel, from the same Radia undulator models, angular magnetic kick maps are calculated, and the insertion device effect on electron beam is simulated using Tracy‐2 tracking code based on symplectic integrator. After these simulations, magnet parameters are fine‐tuned and the maximal acceptable undulator lengths are determined for different straight sections, as functions of minimal gap and with due regard for the electron beam vertical “stay clear” constraint in the case of in‐vacuum undulators. Finally, the optimal undulator period and length are determined as the values providing maximal spectral flux among the pre‐selected undulator cases, already satisfying the requirements concerning the harmonic cut‐off values and the effect on electron beam.
Published Version
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