New chicane magnet design for insertion device straights at the Advanced Light Source

Abstract

A chicane magnet incorporating counter-rotating permanent magnet pairs together with trim coils has been designed for use in the Advanced Light Source (ALS) straights in conjunction with two insertion devices. In particular, this design is being developed for use in the existing beam line (BL) 4 elliptically polarizing undulator (EPU) straight and in the BL11 EPU straight, currently under design and construction. The purpose of the chicane is to provide a fixed angular separation between two successive EPU photon fans, and to correct steering perturbations resulting from EPU polarization state changes. Polarization changes occur on the time scale of one second; associated steering corrections must be accomplished in less than a second. Hysteresis associated with conventional iron core electromagnets prevents fast steering correction to the required precision. This consideration motivated the iron-free design presented here.