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Computing Emittance for Non-Gaussian Beam Distributions

Student: Charles McIntyre

School: Reed College

Mentored By: Todd Satogata

We analyze recent data to compute the emittance and Twiss parameters for the electron beam at Jefferson Lab's Continuous Electron Beam Accelerator Facility (CEBAF). The beam is sent through a focusing quadrupole; after focusing, the beam's intensity as a function of transverse position is measured using wire scanners. We develop tools to fit intensity data with both Gaussian and skew-Gaussian distributions, and use the fit parameters to extract mean-square beam size. Analysis of beam size data as a function of quadrupole strength yields the emittance and Twiss parameters. Parameter values are computed in the horizontal plane at 9 points in the accelerator, and in the vertical plane at 6 points. Values for emittance range between 1 × 10-9 and 6 × 10-9 (±%2). Values for Twiss parameters are found to deviate from design values by up to 2000%, indicating a poorly tuned beam at the time of measurement.
Computing Emittance for Non-Gaussian Beam Distributions