Magnetic field characterization, re-tuning and first operation of the NIST undulator on the Duke 1 GeV storage ring

Originally built for an IR FEL project at the National Institute of Standards and Technology, the NIST undulator was acquired by Duke for use as a soft x-ray source on the 1 GeV storage ring. The Brobeck Division of Maxwell Laboratories constructed this 3.64 m long hybrid-design undulator. Initial Hall probe measurements on the magnetic field distribution of the undulator revealed field errors of more than 0.80% RMS. Initial phase errors for the device were more than 11 deg. A series of in-situ and off-line measurements and modifications were employed to re-tune the magnetic field structure. Initial goals for the device called for the production of strong spectral characteristics through the 5th harmonic. Although rms field errors remained rather high (∼0.75%), phase errors were reduced to less than 5 degrees. A diagnostic beamline including a transmission grating spectrometer and a scanning wire beam profile monitor was constructed to characterize the spatial and spectral characteristics of the radiation. We report on this effort and the resulting first operation of this undulator source