Construction and performance of an elliptically polarized undulator of type Apple-II

Abstract

Ten years ago, an elliptically polarized undulator (EPU) with a periodic length of 56 mm was constructed at the Taiwan Light Source. It was the longest EPU at that time. An electron beam of energy 1.5 GeV and current 300 mA passes through the undulator gap and radiates variously polarized light in the soft X-ray spectral domain. This EPU was extensively used in a wide range of research fields, including inelastic scattering, spin-polarized photoemission spectroscopy, photoelectron emission microscopy, and soft X-ray scattering. In response to increased demand by users with differing experimental requirements and applications, the construction of an EPU with a period of length 46 mm is under way. This investigation describes many aspects of the magnetic design, the structural engineering, and the control system. As magnetic technology is undergoing dramatic advances, advanced mechanical devices, and mechanisms have been included in the new EPU design; this design and its differences from the earlier design are summarized here.

Keywords:

• elliptically polarized undulator
• undulator
• insertion devices
• polarization