UCLA, Los Angeles, USA
We present an algorithm to tomographically reconstruct the 4D phase space of a beam distribution of a high brightness electron beam, based on the use of two fluorescent screens separated by a beamline containing a quadrupole triplet which can be used to impart arbitrary rotations to the beam phase space. The reconstruction method is based on generating a macroparticle distribution which matches the initial profile and then it is iteratively updated using the beam projections on the second screen until convergence is achieved. This process is repeated for many quadrupole current settings. The algorithm is benchmarked against GPT simulations, and then implemented at the UCLA Pegasus beamline to measure the phase space distribution for an upcoming high speed electron microscope experiment.
ANL, Lemont, Illinois, USA
RadiaBeam, Santa Monica, California, USA
UCLA, Los Angeles, California, USA
Private Address, Silver Spring, USA
One of the advantages of relativistic electron beams with microbunching at UV to visible wavelengths is the potential to generate coherent optical transition radiation (COTR) at a metal foil for diagnostics purposes. A significant microbunching fraction of at least 10% is expected for the case of a seed laser at 257.5 nm copropagating with a 343-MeV electron beam through a modulator undulator (3.2 cm period) at the Linac Extension Area (LEA) at Argonne National Laboratory. Diagnostic plans have been made for the COTR based-characterization of the microbunched beam size (~100 microns), divergence (sub-mrad), microbunching fraction, spectrum, and bunch length (sub-ps), as well as coalignment of the laser pulse and electron beam as previously described**. For that case, COTR enhancements over OTR of more than seven million were calculated, and we expect a similar enhancement of coherent optical diffraction radiation (CODR). Thus, we propose the modification of the microbunching diagnostics station to support initial (CODR) experiments with beam transit through an aperture in a metal screen or near a metal edge at the second screen position of the interferometer. We would explore whether the coherence function for CODR provides a complementary beam size monitor and whether COTR and CODR interferences from the two interferometer screens provide divergence and pointing information.
**A.H. Lumpkin and D.W. Rule, Proceedings of FEL19, WEP041, Hamburg, Germany, Aug. 2019, https://JaCoW.org.