Optical transition radiation interferometry (OTRI) has been shown to be avery useful technique to measure the divergence of electron beams with energiesin the range of 15-100 MeV. However, application of this method to low energyor very high quality beams is limited by scattering in the front foil of theinterferometer. To overcome this limitation we propose to use a perforatedfront foil. For the beam energy and hole sizes we are considering, theunscattered beam electrons passing through the holes will produce diffractionradiation (ODR). The total radiation produced from the first and second foilsthen will be a spatially coherent sum of ODR and OTR from unscattered andscattered electrons. By controlling the number and size of the perforations,the inter-foil spacing, the thickness of the first foil and the wavelength andband pass of the observed radiation, the coherent interferences due to theunscattered portion of the beam can be isolated and observed. The visibility ofthese interferences can then be used to determine the rms beam divergence. Wehave developed a general computer code which can be used to calculatediffraction radiation from any type of perforation and another code to computethe ODR-OTR interference pattern for a given set of beam and opticalparameters. These codes are employed in the design of an interferometer tomeasure the divergence of the ATF accelerator operating at 30 MeV. This beamwill be used in an initial proof of principle experiment for the ODR-OTRinterferometer. We present the results of our code calculations which show thatthe expected divergence, 200 micro radians, can be easily measured.
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