Nonintercepting beam size and position monitor using ODR for x-ray FELs

Interest in nonintercepting (NI) beam size and position diagnostics between the undulators of x-ray free-electron lasers (XFELs) is driven by the requirement of beamemittance matching and beam alignment, as well as by the need to minimize radiation damage to the undulator permanent magnets from scattered beam produced by the insertion of converter screens. For these reasons our investigations on optical diffraction radiation (ODR) as relative beam size and position diagnostics are particularly relevant to XFELs. We report the extensions of our studies at 7-GeV beam energy to aspects of the vertical and horizontal polarization components of the ODR near-field and far-field images. The near-field, vertically polarized data are particularly interesting because the vertical field lines at the metal more directly reflect the actual horizontal beam sizes. Although our experiments to date are with mm-scale beams and impact parameters of 1-2 mm, our analytical model indicates that this technique scales with beam size and has sensitivity at the 20- to 50-(micro)m regime with an impact parameter, d = 5 times σy = 100 (micro)m. This is the x-ray FEL intraundulator beam size regime.