Compensation Controls for an Elliptically Polarising Undulator

At the Canadian Light Source (CLS) synchrotron, the addition of the Quantum Materials Spectroscopy Centre (QMSC) beamline requires the addition of an Elliptically Polarizing Undulator (EPU) insertion device to produce photons from the stored electron beam. Unlike the majority of such insertion devices, this EPU requires the production of photons of simultaneous arbitrary elliptical and linear phases, in addition to a range of energies. This EPU is also capable of creating perturbations of the stored electron beam sufficient to cause an interruption of an injection. In order to prevent this, compensation controls have been developed. These controls are accomplished with a combination of Experimental Physics and Industrial Control System (EPICS), mathematical models, and algorithms written in C and MATLAB. INTRODUCTION The Canadian Light Source (CLS) is a synchrotron radiation facility with an electron beam storage ring of 2.9 GeV. For the new Quantum Materials Spectroscopy Centre (QMSC) beamline, the Insertion Device (ID) is of the type Elliptically Polarizing Undulator (EPU) of an APPLE II manner, which uses four girders Q1 −Q4 as the frame for the magnetics as in Fig. 1. APPLE II EPUs are capable of creating photons both with elliptical polarization ΦE and linear polarization ΦL . However, in operation, generally only one of ΦE and ΦL are non-zero. This, combined with undulator gap, creates a system with two degrees of freedom.