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Title: Off-axis beam dynamics in rf-gun-based electron photoinjectors

Abstract

The need to operate an rf-gun-based electron photoinjector with a beam emitted away from the cathode center can occur under various circumstances. First, in some cases the cathode can be affected by ion back-bombardment that progressively reduces the quantum efficiency (QE) in its center, making off-axis operation mandatory; second, in some cases the drive laser intensity can be sufficiently high to generate QE depletion in the cathode area illuminated by the laser, forcing off-axis operation; last, in cathodes with nonuniform QE distribution it could be convenient to operate off axis to exploit a better QE. However, operation in this mode may lead to growth of the projected transverse beam emittances due to correlations between the transverse and longitudinal degrees of freedom that are introduced within the gun and downstream rf cavities. A strategy is described to mitigate this emittance growth by allowing the beam to propagate along a carefully tuned off-axis trajectory in downstream rf cavities to remove the time-dependent rf kicks introduced in the gun. Along this trajectory, short range wakefields do not degrade the emittance, and long range wakefields degrade the emittance for very high repetition rate only.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1333316
Alternate Identifier(s):
OSTI ID: 1378938
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Name: Physical Review Accelerators and Beams Journal Volume: 19 Journal Issue: 11; Journal ID: ISSN 2469-9888
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Huang, R., Mitchell, C., Papadopoulos, C., Qian, H., Venturini, M., Qiang, J., Filippetto, D., Staples, J., Jia, Q., and Sannibale, F. Off-axis beam dynamics in rf-gun-based electron photoinjectors. United States: N. p., 2016. Web. doi:10.1103/PhysRevAccelBeams.19.113401.
Huang, R., Mitchell, C., Papadopoulos, C., Qian, H., Venturini, M., Qiang, J., Filippetto, D., Staples, J., Jia, Q., & Sannibale, F. Off-axis beam dynamics in rf-gun-based electron photoinjectors. United States. https://doi.org/10.1103/PhysRevAccelBeams.19.113401
Huang, R., Mitchell, C., Papadopoulos, C., Qian, H., Venturini, M., Qiang, J., Filippetto, D., Staples, J., Jia, Q., and Sannibale, F. Tue . "Off-axis beam dynamics in rf-gun-based electron photoinjectors". United States. https://doi.org/10.1103/PhysRevAccelBeams.19.113401.
@article{osti_1333316,
title = {Off-axis beam dynamics in rf-gun-based electron photoinjectors},
author = {Huang, R. and Mitchell, C. and Papadopoulos, C. and Qian, H. and Venturini, M. and Qiang, J. and Filippetto, D. and Staples, J. and Jia, Q. and Sannibale, F.},
abstractNote = {The need to operate an rf-gun-based electron photoinjector with a beam emitted away from the cathode center can occur under various circumstances. First, in some cases the cathode can be affected by ion back-bombardment that progressively reduces the quantum efficiency (QE) in its center, making off-axis operation mandatory; second, in some cases the drive laser intensity can be sufficiently high to generate QE depletion in the cathode area illuminated by the laser, forcing off-axis operation; last, in cathodes with nonuniform QE distribution it could be convenient to operate off axis to exploit a better QE. However, operation in this mode may lead to growth of the projected transverse beam emittances due to correlations between the transverse and longitudinal degrees of freedom that are introduced within the gun and downstream rf cavities. A strategy is described to mitigate this emittance growth by allowing the beam to propagate along a carefully tuned off-axis trajectory in downstream rf cavities to remove the time-dependent rf kicks introduced in the gun. Along this trajectory, short range wakefields do not degrade the emittance, and long range wakefields degrade the emittance for very high repetition rate only.},
doi = {10.1103/PhysRevAccelBeams.19.113401},
journal = {Physical Review Accelerators and Beams},
number = 11,
volume = 19,
place = {United States},
year = {Tue Nov 22 00:00:00 EST 2016},
month = {Tue Nov 22 00:00:00 EST 2016}
}

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