The number of effective poles of a wiggler on a X-ray beamline: a userʹs viewpoint

With a beamline using a focusing element, a rather lengthy wiggler source will enlarge the beam size at sample position. In this report, the effect of the length of a wiggler on the beam properties at sample position is studied. The results show that for a 25 poles wiggler of 2.5 m with a focusing element located at 20 m downstream, the effective pole is reduced to approximately 20 poles for the typical experiments that required beam size of less than 1 mm.