AttoSHINE: Generation of continuous-wave terawatt-scale attosecond X-ray pulses at SHINE

TL;DR

This work demonstrates a universal self-chirping mechanism to generate terawatt-scale attosecond X-ray pulses at a continuous-wave XFEL, specifically SHINE. By shaping the bunch in the linac to create a strong energy chirp and using a large positive $R_{56}$ in a dogleg for final compression, AttoSHINE achieves sub-femtosecond X-ray pulses at MHz repetition without new hardware. FEL simulations show average pulse durations around 300 as with sub-TW to TW peak powers at hard X-ray energies (e.g., 6 keV), and ~470 as pulses with high peak power at soft X-ray energies (1 keV), including realistic jitter. The results indicate CW attosecond X-ray generation is feasible and transformative for real-time electronic dynamics studies, with further gains anticipated from fully CW superconducting facilities.

Abstract

Attosecond X-ray pulses are a critical tool for tracking ultrafast electron dynamics in condensed matter, molecular systems, and strongly correlated materials. Recent breakthroughs have pushed X-ray free electron lasers (XFELs) into the attosecond domain, significantly surpassing their previous femtosecond capabilities. Building on these advancements, this work investigates the potential of the Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE), China's first continuous-wave (CW) XFEL, to generate intense attosecond X-ray pulses, thereby offering transformative capabilities for X-ray science. Through comprehensive start-to-end simulations, we show that SHINE is capable of producing hard X-ray pulses with peak powers reaching the terawatt-scale and average pulse durations of approximately 300 as. This is achieved using a self-chirping scheme within the existing machine configuration, requiring no additional hardware. Our findings demonstrate that CW XFELs can generate intense attosecond X-ray pulses at megahertz repetition rates, opening new opportunities for real-time studies of electronic dynamics in complex systems.

Figures (11)

• Figure 1: Schematic illustration of the self-chirping scheme, which includes two linac sections, a chicane, a dogleg section, and an undulator. (a)-(c) show the evolution of the longitudinal phase space and corresponding current profiles (gray lines). Bunch head is to the left.
• Figure 2: Layout of AttoSHINE with LTU1 beamline shown as a representative beamline section. Here, L1, LH, L2, and L3 denote linac sections, BC1 and BC2 are bunch compression sections, and FEL1 refers to the undulator section. The grey box highlights the layout of the deflection section of the LTU1 beamline.
• Figure 3: Optical functions and $R_{56}$ along the LTU1 beamline. (a) the original design; (b) an optimized lattice with a $R_{56}$ of 2.1 mm while remaining achromatic.
• Figure 4: Longitudinal phase spaces of the head-current spike case (a, b) and tail-current spike case (c, d). The left corresponds to the end of BC2; the right corresponds to the end of L4. Grey lines represent the current profile. Bunch head is to the left.
• Figure 5: Longitudinal phase space and current profile of different settings. (a)-(d) refer to the end of BC2: (a) head-current spike case with LH + $0.1^\circ$, (b) head-current spike case with LH - $0.1^\circ$, (c) tail-current spike case with LH + $0.1^\circ$, and (d) tail-current spike case with LH - $0.1^\circ$. (e)-(h) refer to the end of L4: (e) head-current spike case with LH + $0.1^\circ$, (f) head-current spike case with LH - $0.1^\circ$, (g) tail-current spike case with LH + $0.1^\circ$, and (h) tail-current spike case with LH - $0.1^\circ$. Bunch head is to the left.