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Cascaded high-gradient terahertz-driven acceleration of relativistic electron beams


Terahertz-driven acceleration has recently emerged as a route for delivering ultrashort bright electron beams efficiently, reliably and in a compact set-up. Many working schemes and key technologies related to terahertz-driven acceleration have been successfully demonstrated and are being developeds1,2,3,4,5,6,7,8,9,10. However, the achieved acceleration gradient and energy gain remain low, and the potential physics and technical challenges in the high-energy regime are still underexplored. Here we report whole-bunch acceleration of relativistic beams with an effective acceleration gradient of up to 85 MV m–1 in a single-stage configuration and demonstrate a cascaded terahertz-driven acceleration scheme of relativistic beams with an energy gain of 204 keV. These proof-of-principle results represent a critical advance towards high-energy terahertz-driven acceleration of relativistic beams, are scalable and have great potential to provide high-quality beams, with implications for future terahertz-driven electron sources and related scientific discoveries.

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Fig. 1: Single-stage terahertz-driven linac.
Fig. 2: Single-stage terahertz-driven acceleration and energy modulation.
Fig. 3: Cascaded terahertz-driven linacs.
Fig. 4: Observation of cascaded terahertz-driven acceleration.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.


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We acknowledge W. Jiang and S. Ji, at the State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, for their help with the tantalum target coating. This work is supported by the National Natural Science Foundation of China (NSFC grant no. 11835004) and Science Challenge Project (no. TZ2018005).

Author information

Authors and Affiliations



H.X., W.H., L.Y. and Y.D. conceived and designed the experiment. H.X. built and conducted the experiment with the help from Q.T., L.Y., Y.D., S.G., Y.L., W.H. and C.T. H.X. designed the DLW and the tapered horn coupler with the help of J.S. H.X. developed and performed the simulations for data evaluation and interpretation of results. H.X. wrote the manuscript with contributions from W.H., L.Y., R.L., Y.D. and C.T. W.H. provided management and oversight to the project.

Corresponding author

Correspondence to Wenhui Huang.

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The authors declare no competing interests.

Additional information

Peer review information Nature Photonics thanks Rasmus Ischebeck, Stefan Karsch and Emilio Nanni for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 TTX beamline and the laser splitting setup.

The TTX beamline (a) and the laser splitting setup (b).

Extended Data Fig. 2 THz linac.

a, Frequency map for different DLW dimensions when vp = 0.9999c. b, Calculated normalized energy gain for different DLW dimensions when vp = 0.9999c and f0 = 0.6 THz. c, Dispersion curve of the designed DLW. d, Normalized magnitude of the longitudinal electric field along the radial axis. e, Calculated coupling of the horn coupler. f, Simulation results of megaelectronvolt-level THz-driven acceleration using the designed DLW for single-stage and cascaded configurations.

Supplementary information

Supplementary Information

Contents: (1) TTX beamline; (2) shot-to-shot energy jitter; (3) dispersion; (4) effective frequency bandwidth; (5) transverse force; (6) beam matching; (7) acceleration efficiency. Supplementary Figs. 1–4 and refs. 1–6.

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Xu, H., Yan, L., Du, Y. et al. Cascaded high-gradient terahertz-driven acceleration of relativistic electron beams. Nat. Photonics 15, 426–430 (2021).

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