Design of an emittance measurement device for the C-band photocathode RF gun

Chen Weiwen; Jiang Shimin; Liu Renhong; Yang Tao; Huang Weiling; Yang Renjun; Li Xiao

doi:10.11884/HPLPB202537.250038

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Chen Weiwen, Jiang Shimin, Liu Renhong, et al. Design of an emittance measurement device for the C-band photocathode RF gun[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250038

Citation:

Chen Weiwen, Jiang Shimin, Liu Renhong, et al. Design of an emittance measurement device for the C-band photocathode RF gun[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250038

Chen Weiwen, Jiang Shimin, Liu Renhong, et al. Design of an emittance measurement device for the C-band photocathode RF gun[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250038

Citation:

Chen Weiwen, Jiang Shimin, Liu Renhong, et al. Design of an emittance measurement device for the C-band photocathode RF gun[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250038

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Design of an emittance measurement device for the C-band photocathode RF gun

doi: 10.11884/HPLPB202537.250038

Chen Weiwen^{1, 2, 3
,},
Jiang Shimin^{1, 3},
Liu Renhong^{1, 3},
Yang Tao^{1, 3},
Huang Weiling^{1, 2, 3},
Yang Renjun^{1, 2, 3
,
,},
Li Xiao^{1, 2, 3}

1.
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
2.
University of Chinese Academy of Sciences, Beijing 100049, China
3.
Spallation Neutron Source Science Center, Dongguan 523803, China

Received Date: 2025-02-27
Accepted Date: 2025-07-18
Rev Recd Date: 2025-08-05

Available Online: 2025-09-25

Abstract

Abstract

Background
To enhance the performance of the next-generation X-ray free electron laser (XFEL), a photocathode RF gun capable of providing the required high-quality electron beam with a small emittance has been a significant research objective. In comparison to the conventional L-band or S-band RF gun, the C-band RF gun features a higher acceleration gradient above 150 MV/m and the ability to generate a small-emittance beam. Low-emittance electron beams are critical for enhancing XFEL coherence and brightness, driving demand for advanced RF gun designs. For a bunch charge of 100 pC, a normalized emittance of less than 0.2 mm.mrad has been expected at the gun exit.
Purpose
This paper presents the design of an emittance measurement device, which can accurately measure such a small emittance at the C-band RF gun exit to ensure beam quality for XFEL applications.
Methods
To achieve the desired accuracy, the primary parameters —slit width, slit thickness, and beamlet-drift length—have been systematically optimized through numerical simulations using Astra and Python based on the single-slit-scan method. Dynamic errors, including motor displacement and imaging resolution, were quantified to ensure measurement reliability.
Results
The evaluations indicate that the measurement error of 95% emittance is less than 5%, employing a slit width of 5 μm, a slit thickness of 1 mm, and a beamlet-drift length of 0.11 m under dynamic conditions.
Conclusions
This optimized emittance measurement device supports precise beam quality characterization for XFELs, offering potential for further advancements in electron beam diagnostics.
- C-band RF gun,
- beam with high quality,
- normalized beam emittance,
- emittance measurement device,
- single-slit-scan method

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References(39)

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