Skip to main content

The Center for Bright Beams, A National Science Foundation Science and Technology Center

Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order

Electron beams in accelerators are focused and controlled at high precision by electromagnetic lenses, such as solenoids and bunching cavities. Unfortunately, no electromagnetic lens is perfect due to unavoidable aberrations in the fields that ultimately reduce the achievable quality of the electron beam. Small, aberrant fields from electromagnetic lenses have an inconsequential role in many accelerator applications, but have a massive impact on applications demanding small beam sizes and emittances, such as ultrafast electron microdiffraction at Cornell’s MEDUSA beamline. This is the first experimental demonstration of a technique that corrects magnetic field aberrations up to sextupole order in a low emittance beamline. This work enabled the exciting application of ultrafast electron microdiffraction at MEDUSA for studying materials at ultrafast timescales, and can be readily used by other electron microdiffraction facilities.

an image showing three black rectangles with blue gradient glowing shapes in the middle of each
Experimental correction of the sextupole moment. From left to right the beam profiles are taken with: the sextupole corrector off, the sextupole corrector anti-aligned with sextupole moment at a large current, the sextupole correcter anti-aligned at a strength to cancel the sextupole moment.

This result directly addresses the CBB goal of probing the ultimate limits of brightness conservation in the presence of collective effects in low MTE photoinjector beamlines. It also shows that it is possible to correct for the vast majority of the sextupole aberration created by beamline optics in photoinjectors with a downstream sextupole magnet and simple visual correction scheme.


M. Gordon, W. H. Li, M. B. Andorf, A. C. Bartnik, C. J. R. Duncan, M. Kaemingk, C. A. Pennington, I. V. Bazarov, Y.-K. Kim, and J. M. Maxson, “Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order,” Phys. Rev. Accel. Beams, vol. 25, no. 8, p. 084001, Aug. (2022) [Online] Available: