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<p>The application of radiofrequency (RF) electron guns operating at cryogenic temperatures can enhance the performance of a photoinjector. The low emittance and increased brightness of the electron beams resulting from the high gradient in the cryogenic photoinjector make it possible to improve the performance of new light sources. As an upgrading scheme for the Shanghai Soft X-ray Free-Electron Laser, this study explores a novel photocathode RF gun by introducing the <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1744_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {TM}_{\textrm{02}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>TM</mtext> <mtext>02</mtext> </msub> </math></EquationSource> </InlineEquation> mode into the cathode cell of a 2.6-cell electron gun, which improves the RF performance, particularly in terms of the monopole field. Furthermore, the optimized cathode cell with the <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41365_2025_1744_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hbox {TM}_{02}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>TM</mtext> <mn>02</mn> </msub> </math></EquationSource> </InlineEquation> mode can reduce the errors resulting from installation and decrease the dark current with alternative cathodes. In this study, the beam dynamics in a photoinjector were optimized using a 500-pC, 5-ps beam, and its feasibility was examined. This paper presents the entire RF design process, including the adjustment of the RF structure, coupler design, local field, and multipole mode suppression to provide theoretical guidance for subsequent manufacturing and assembly.</p>

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Design of a cryogenic photocathode gun with a novel TM02 mode coupler for low emittance

  • 期刊论文

  • 发表日期：

    2025年8月13日

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  • Jia-Hao Tian,
  • Cheng Wang,
  • Wen-Cheng Fang,
  • Zhen-Tang Zhao

摘要

The application of radiofrequency (RF) electron guns operating at cryogenic temperatures can enhance the performance of a photoinjector. The low emittance and increased brightness of the electron beams resulting from the high gradient in the cryogenic photoinjector make it possible to improve the performance of new light sources. As an upgrading scheme for the Shanghai Soft X-ray Free-Electron Laser, this study explores a novel photocathode RF gun by introducing the \(\hbox {TM}_{\textrm{02}}\) TM 02 mode into the cathode cell of a 2.6-cell electron gun, which improves the RF performance, particularly in terms of the monopole field. Furthermore, the optimized cathode cell with the \(\hbox {TM}_{02}\) TM 02 mode can reduce the errors resulting from installation and decrease the dark current with alternative cathodes. In this study, the beam dynamics in a photoinjector were optimized using a 500-pC, 5-ps beam, and its feasibility was examined. This paper presents the entire RF design process, including the adjustment of the RF structure, coupler design, local field, and multipole mode suppression to provide theoretical guidance for subsequent manufacturing and assembly.