Optimization of a three-axes teslameter for the calibration of the next generation undulators

Abstract

The measurement of a magnetic field in three-axes and with high spatial resolution has several industrial and experimental applications. One specific experimental application involves characterizing the field map of insertion devices in free electron lasers. This work presents the development of a new, reduced form-factor, three-axes digital teslameter. This instrument will be used to characterize the SwissFEL insertion devices at the Paul Scherrer Institute (PSI) for the Athos soft X-ray beamline. Together with a Hall probe at the centre of the cross-sectional area of the undulator, the setup will traverse along the full undulator length on a specifically designed rig with minimal vibrations, thus acquiring a full magnetic field map in the three-axes. The teslameter incorporates analogue signal conditioning for the three-axes interface to a Hall probe, a linear absolute encoder interface and a high resolution 24-bit analogue-to-digital converter. This contrasts to the old instrumentation setup used which only consists of the analogue circuitry with digitization being done externally to the instrument by proprietary hardware. The new instrument also provides a very accurate magnetic field map in the μT range with simultaneous readings from the position encoder at an accuracy of ±3 μm. The novelty of the instrument is the provision of an integrated tailored solution which is very compact in size and with comparable performance to the best state-of-the-art teslameters that are currently available on the market. A brief background on magnetic field instrumentation is initially given which is followed by the actual hardware development of the novel teslameter. The standardized calibration procedure that is critical in optimizing the performance of this precision instrument follows. The performance results obtained outline the noise, measuring precision, repeatability and frequency response of the instrument among other parameters. These are analysed to finally devise the insightful knowledge on the magnetic properties of insertion devices that need to be modelled and characterised.