Speaker
Description
The application to FELs has become a research interest after improvements in laser-plasma-accelerator (LPA) beam quality and reliability, [1,2]. The goal is for more compact light sources due to the high gradients in the LPA. However, the FEL output from ultra-short LPA electron bunches (at the 20-fs level) is dominated by the rapid slippage of the beam behind the optical pulse in two LPA-FEL experiments at 27 nm [1] and 420 nm [2]. When the ratio of the electron bunch length to slippage is close to one, exponential gain is limited even in an rf-linac-driven FEL at 530 nm [3]. This empirical limit is supported by simulations using the MINERVA code at 420-nm. In ref. 2, the optical pulse slips ahead of the electrons over the first 1-m of the undulator. However, the electron bunch has been modulated and after ballistic bunching further radiation is found. Hence, this acts like an optical klystron where the first meter of the undulator acts as the modulator and the remainder of the undulator is the radiator. The code’s unique feature being able to apply slippage 30 times per undulator period (instead of once as in some codes) is required to resolve the rapid slippage [2].
Funding Agency
*This work was supported (HPF) by the United States Department of Energy under contract DE-SC0024397.
Footnotes
[1] W. Wang et al., Nature 595, 516 (2021).
[2] S. Barber et al., Phys. Rev. Lett. 135, 055001 (2025).
[3] S.V. Milton et al., Science 292, 1953 (2001).
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