• Open Access

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

David H. Dowell, Feng Zhou, and John Schmerge
Phys. Rev. Accel. Beams 21, 010101 – Published 17 January 2018

Abstract

Weak, rotated magnetic and radio frequency quadrupole fields in electron guns and injectors can couple the beam’s horizontal with vertical motion, introduce correlations between otherwise orthogonal transverse momenta, and reduce the beam brightness. This paper discusses two important sources of coupled transverse dynamics common to most electron injectors. The first is quadrupole focusing followed by beam rotation in a solenoid, and the second coupling comes from a skewed high-power rf coupler or cavity port which has a rotated rf quadrupole field. It is shown that a dc quadrupole field can correct for both types of couplings and exactly cancel their emittance growths. The degree of cancellation of the rf skew quadrupole emittance is limited by the electron bunch length. Analytic expressions are derived and compared with emittance simulations and measurements.

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  • Received 25 July 2017

DOI:https://doi.org/10.1103/PhysRevAccelBeams.21.010101

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Accelerators & Beams

Authors & Affiliations

David H. Dowell*, Feng Zhou, and John Schmerge

  • SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

  • *dowell@slac.stanford.edu

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Vol. 21, Iss. 1 — January 2018

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