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Title: Area-preserving scheme for efficiency enhancement in single-pass tapered free electron lasers

Abstract

Efficiency enhancement of a single-pass short-wavelength high-gain tapered free electron laser (FEL) has recently been intensively studied. The goal is to sustain the growth of radiation power in the post-saturation regime. Among the various schemes, the undulator tapering is considered an effective route to achieve higher power extraction efficiency. The tapering strategy can be of constant or varying resonant phase along the undulator axis. In this paper we propose an efficiency-enhancement scheme based on preservation of the longitudinal phase space area which ensures trapping of resonant particles in the ponderomotive bucket as long as possible along the undulator axis before significant particle depletion occurs. In the meanwhile such a scheme takes advantage of the increase of the radiation field amplitude to precipitate the particle deceleration process at the middle stage of undulator tapering. We analyze such an area-preserving scheme of undulator tapering by formulating the post-saturation FEL interaction in a one-dimensional (1-D) model via introduction of the particle trapping fraction. The output performance is evaluated through numerical iteration and confirmed with 1-D particle tracking simulations. The results show that the optimal power extraction efficiency based on the proposed scheme, together with a prebunched beam, can be greatly improved within relativelymore » short taper length compared with other schemes before radiation diffraction effect becomes significant. Besides, the undesired sideband effects are found to be effectively suppressed. For the proposed area-preserving taper scheme, we also derive an analytical approximate formula for the resonant phase as a function of undulator axis. In conclusion, we expect that the analysis can shed light on the aim to further enhance the power extraction efficiency in single-pass tapered FELs.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5];  [6]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States); Huazhong Univ. of Science and Technology, Hubei (China)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. Pohang Univ. of Science and Technology, Pohang (Republic of Korea)
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States); Chinese Academy of Sciences, Shanghai (China); Univ. of Chinese Academy of Sciences, Beijing (China)
  5. SLAC National Accelerator Lab., Menlo Park, CA (United States); Univ. of Sciences and Technology of China, Anhui (China)
  6. SLAC National Accelerator Lab., Menlo Park, CA (United States); Chinese Academy of Sciences, Beijing (China); Univ. of Chinese Academy of Sciences, Beijing (China)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1490886
Grant/Contract Number:  
AC02-76SF00515; FWP-2013-SLAC-100164
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Additional Journal Information:
Journal Volume: 913; Journal Issue: C; Journal ID: ISSN 0168-9002
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; Free electron lasers; Undulator tapering; Efficiency enhancement

Citation Formats

Tsai, C. -Y., Emma, C., Wu, J., Yoon, M., Wang, X., Yang, C., and Zhou, G. Area-preserving scheme for efficiency enhancement in single-pass tapered free electron lasers. United States: N. p., 2018. Web. doi:10.1016/j.nima.2018.10.062.
Tsai, C. -Y., Emma, C., Wu, J., Yoon, M., Wang, X., Yang, C., & Zhou, G. Area-preserving scheme for efficiency enhancement in single-pass tapered free electron lasers. United States. doi:10.1016/j.nima.2018.10.062.
Tsai, C. -Y., Emma, C., Wu, J., Yoon, M., Wang, X., Yang, C., and Zhou, G. Mon . "Area-preserving scheme for efficiency enhancement in single-pass tapered free electron lasers". United States. doi:10.1016/j.nima.2018.10.062.
@article{osti_1490886,
title = {Area-preserving scheme for efficiency enhancement in single-pass tapered free electron lasers},
author = {Tsai, C. -Y. and Emma, C. and Wu, J. and Yoon, M. and Wang, X. and Yang, C. and Zhou, G.},
abstractNote = {Efficiency enhancement of a single-pass short-wavelength high-gain tapered free electron laser (FEL) has recently been intensively studied. The goal is to sustain the growth of radiation power in the post-saturation regime. Among the various schemes, the undulator tapering is considered an effective route to achieve higher power extraction efficiency. The tapering strategy can be of constant or varying resonant phase along the undulator axis. In this paper we propose an efficiency-enhancement scheme based on preservation of the longitudinal phase space area which ensures trapping of resonant particles in the ponderomotive bucket as long as possible along the undulator axis before significant particle depletion occurs. In the meanwhile such a scheme takes advantage of the increase of the radiation field amplitude to precipitate the particle deceleration process at the middle stage of undulator tapering. We analyze such an area-preserving scheme of undulator tapering by formulating the post-saturation FEL interaction in a one-dimensional (1-D) model via introduction of the particle trapping fraction. The output performance is evaluated through numerical iteration and confirmed with 1-D particle tracking simulations. The results show that the optimal power extraction efficiency based on the proposed scheme, together with a prebunched beam, can be greatly improved within relatively short taper length compared with other schemes before radiation diffraction effect becomes significant. Besides, the undesired sideband effects are found to be effectively suppressed. For the proposed area-preserving taper scheme, we also derive an analytical approximate formula for the resonant phase as a function of undulator axis. In conclusion, we expect that the analysis can shed light on the aim to further enhance the power extraction efficiency in single-pass tapered FELs.},
doi = {10.1016/j.nima.2018.10.062},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
issn = {0168-9002},
number = C,
volume = 913,
place = {United States},
year = {2018},
month = {10}
}

Journal Article:
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