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Description
Ultrafast Electron Diffraction (UED) is an imaging technique used to observe the atomic structure of matter and its dynamics through the scattering of a pulsed electron beam.
The performance of a UED beamline depends on electron beam parameters such as beam size, bunch length, bunch charge and beam energy which are affected by UED machine parameters including strength of solenoid and RF phase. However, these beam parameters cannot be optimized simultaneously due to their mutual correlations and trade-offs, such as those caused by space-charge effects.
At PAL, an MeV-UED facility for both solid and gas-phase imaging was constructed. In this paper, we introduce the current status of the MeV-UED apparatus at PAL-eLABs together with measurements of several key laser and electron beam parameters. Additionally, we discuss the implementation of an online optimization process using constrained multi-objective Bayesian optimization. We also compare this with multi-objective regionalized Bayesian optimization, which restricts the search for the next observation point to a hyperrectangular trust region whose center and width vary during the optimization process.
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