Calculated performance of ALS undulator U3.9: Operation at dual wavelengths and high harmonics

Abstract

Calculations of the spectral output of Advanced Light Source undulator U3.9 are presented. Effects of electron beam emittance and energy spread are included, and undulator magnet field errors are treated approximately so usable estimates of the output of high-harmonic radiation can be made. These calculations indicate that several harmonics can be used simultaneously for obtaining soft X-rays in the λ = 23–44 Å “water window” spectral range. In addition, it is shown that there is an intermediate range of photon energies (∼1–3 keV) where high harmonic undulator radiation is significantly affected by electron beam energy spread and undulator magnet field errors, yet where U3.9 will still outperform ALS wiggler W13.6 for many applications. This intermediate zone between pure undulator and pure wiggler performance may prove useful for extending the energy range at which brightness-sensitive experiments can be done at storage rings of a given electron beam energy.