Abstract: | In modern third generation synchrotron sources, undulators have become the principal source of X-rays and today a brilliance close to 1021 photons/sec?mm2?mrad?0.1%BW is routinely attained for photon energies of 10 keV. However, generating brilliant beams of photons with energies of 50 keV and above leads to conflicting choices for the undulator parameters as the following analysis shows. |