EXPERIMENTAL CHARACTERIZATION OF APS UNDULATOR-A AT HIGH PHOTON ENERGIES (50-200 KEV)

The considerable intensity of Advanced Photon Source (APS) undulator A as a source of high-energy X-rays permits the performance of numerous types of experiments that require such photon energies. Measured and calculated properties, in the 50-200 keV range, of the X-ray beam from undulator A, installed in sector 1 of the APS, are presented. The flu x spectra observed at various gaps agree well with calculations that i ncorporate the actual magnetic field within the device and the emittan ce and energy spread of the stored positrons. The field errors and ene rgy spread cause the X-ray beam to lose undulator radiation properties at high energies, as seen in the smeared-out spectral harmonics and i ncreased beam divergence, giving resemblance to a low-K wiggler source . Owing to the wiggler-like behavior in this photon-energy range, the optimal operating condition for undulator A is in the vicinity of the closed-gap setting, corresponding to a maximum critical energy.