Two-dimensional Synchrotron Beam Shape Characterization using Interferometric Closure Amplitudes

Abstract: Synchrotron radiation interferometry (SRI) is widely used in particle accelerators to monitor the transverse beam profile, and thus the critical beam emittance parameter. We introduce a novel technique to SRI using closure amplitudes, inspired by radio interferometry, to determine the two-dimensional profile of the synchrotron beam. Previous techniques have required multiple interferograms or accurate estimates of the non-uniform aperture illuminations. In contrast, our method using closure amplitudes avoids the need to estimate the aperture illuminations while determining the two-dimensional beam shape from a single interferogram. The invariance of closure amplitudes to even time-varying aperture illuminations makes it suitable to longer averaging intervals, with potential to reducing data rates and computational overheads. Using data from the ALBA synchrotron light source and having validated the results against existing methods, this paper represents one of the first real-world applications of interferometric closure amplitudes to directly determine the light source shape.