Title: Microbunching-instability-induced sidebands in a seeded free-electron laser

Abstract

Measurements of the multishot-averaged, soft x-ray, self-seeding spectrum at the LCLS free-electron laser often have a pedestal-like distribution around the seeded wavelength, which limits the spectral purity and can negatively affect some user applications not employing a post-undulator monochromator. In this paper, we study the origins of such pedestals, focusing on longitudinal phase space modulations produced by the microbunching instability upstream of the free-electron laser (FEL) undulator. Furthermore, we show from theory and numerical simulation that both energy and density modulations can induce sidebands in a high-gain, seeded FEL whose fractional strength typically grows as the square of the undulator length. The results place a tight constraint on the longitudinal phase space uniformity of the electron beam for a seeded FEL, possibly requiring the amplitude of long-wavelength modulations to be much smaller than the typical incoherent energy spread if the output sideband power is to remain only a couple percent or less of the amplified seed power.

Authors:

Zhang, Zhen; Lindberg, Ryan; Fawley, William M.; Huang, Zhirong; Krzywinski, Jacek; Lutman, Alberto; Marcus, Gabriel; Marinelli, Agostino

Publication Date:

Mon May 02 00:00:00 EDT 2016

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1250549

Alternate Identifier(s):

OSTI ID: 1240361

Report Number(s):

SLAC-PUB-16487
Journal ID: ISSN 2469-9888; PRABFM; 050701

Grant/Contract Number:  

AC02-76SF00515; AC02-06CH11357

Resource Type:

Journal Article: Published Article

Journal Name:

Physical Review Accelerators and Beams

Additional Journal Information:

Journal Name: Physical Review Accelerators and Beams Journal Volume: 19 Journal Issue: 5; Journal ID: ISSN 2469-9888

Publisher:

American Physical Society

Country of Publication:

United States

Language:

English

Subject:

43 PARTICLE ACCELERATORS; ACCPHY, XFEL