Characterization of insertion devices using a micro-magnetic measurement bench

Abstract

Light sources are structures that produce intense beams of electromagnetic light such as X-rays. The produced light can be used in various research fields such as the study of material’s structure and dynamics at a molecular and atomic levels. The Swiss Free Electron Laser (SwissFEL) and Swiss Light Source (SLS) are two examples of light sources that are operated by the Paul Scherrer Institute (PSI) in Switzerland. An undulator is an insertion device that is the key component to generate the desired electromagnetic light with great intensity and the ability for tuning over a wide range of wavelengths. Undulators are constructed from a series of magnetic elements that create a magnetic field along the device forcing accelerated electrons, such as those from free electron laser, to oscillate and radiate light in a desired wavelength. It is essential to characterize undulators to ensure the correct electromagnetic light is generated and an overall optimal performance of the light source structure is maximised. Magnetic measurement benches play a crucial role in this process by utilizing magnetic field sensors such as Hall probes to measure the magnetic field profile and analyse the properties of insertion devices. At PSI, the new generation of undulators are to be installed inside a narrow vacuum chamber which results in a more constrained characterization environment, hence, the need for a miniature magnetic measurement bench that can navigate inside the narrow chamber, measure the magnetic field with high precision and accuracy on-site is of high significance. Given the physical constraints of the new generation of undulators, and the lengthy process of commissioning and deploying new ones, the need for a compact, precise and modular measurement bench is of high importance. This dissertation follows the improvements on the implemented prototype of a micro magnetic measurement bench and the integration of all systems on one single printed circuit board, such that all components can travel freely along the undulator while correcting the Hall probe sensor position drifts in 2-degrees of freedom. The traversal movement is achieved via a linear motor, and the probe drift correction is tracked via the use of precision laser positioning system. The corrections are then performed via 2 mechanical stages linked to 2 miniature motors. The magnetic measurement and data acquisition is performed by a previously developed small form-factor, 3- axes Teslameter. The bench was tested on a prototype undulator with passive force compensation side magnets which is planned to be utilised in an upcoming upgrade to the SLS facility (upgrade to SLS2.0). The prototype undulator with force compensation magnets was characterised nonetheless using the implemented bench and the effect of the side magnets on the field enhancing magnets was studied and quantified.