Generation of extremely bright, coherent synchrotron radiation in a short wavelength range is of remarkable interest in the synchrotron light source community. In this paper, a novel technique is adopted to produce coherent radiation, which uses an angular dispersion mechanism to enhance the microbunching of electrons by introducing a slight energy modulation in the long straight section of the storage ring. For this purpose, a lattice design of an extreme low emittance storage ring with 3.5 GeV energy is presented in this paper, which employs a higher-order achromat concept. We show the design results of the multibend achromat lattice with an emittance of 20 pm rad and a circumference of 900 m. Numerical simulation results demonstrate that this angular dispersion-induced microbunching scheme can be used to generate coherent radiation near the soft x-ray region, the repetition rate can reach 10 kHz, and the spectral brightness can reach $2.3\times {10}^{24}\mathrm{photons}{\mathrm{s}}^{-1}{\mathrm{mm}}^{-2}{\mathrm{mrad}}^{-2}$ ${(0.1\%\mathrm{bandwidth})}^{-1}$.

The generation of fully coherent and femtosecond time-scale radiation pulses in the X-ray regime is one of the most common demands of ring-based synchrotron light source users. In this paper, a method that utilizes the recent proposed angular dispersion induced microbunching technique to convert external light from high-harmonic generation (HHG) to coherent light at shorter wavelength is proposed. Numerical simulations using the practical parameters of a diffraction-limited storage ring demonstrate the generation of coherent pulse trains with photon energy as high as 2 keV, pulse duration as short as ∼10 fs and high peak brightness directly from an HHG source at 13 nm.

The combination of reversible angular dispersion-induced microbunching (ADM) and the rapid damping storage ring provides a storage-ring-based light source with the capability to produce longitudinal coherent radiation with a high repetition rate. This paper presents a prototype design for a test facility based on the study by Jiang et al. [Sci. Rep. (2022), 12, 3325]. The modulation–demodulation section is inserted into a long straight section of the storage ring instead of a bypass line, which poses great challenges for the optimization of the nonlinear dynamics of the storage ring. However, this design avoids the challenging injection and extraction system connecting to the bypass line. To utilize mature laser technology and reduce the difficulty of the reversible ADM lattice design, we use a long-wavelength 1030 nm seed laser. In the simulation, we achieved 20th harmonic radiation with a bunching factor of about 7.2%. The growth rate of vertical emittance and energy spread of the electron beam for a single pass are about 11% and 0.02%, respectively. When the energy of the electron beam is 800 MeV and two sets of damping wigglers are employed, the damping time in the vertical plane is reduced to 8.31 ms. This results in a 438 kHz repetition rate of the coherent radiation at the new equilibrium state.

High-average-power extreme ultraviolet (EUV) sources are essential for large-scale nanoscale chip manufacturing, yet commercially available laser-produced plasma sources face challenges in scaling to the kilowatt level. We propose a novel scheme that combines the high repetition rate of a diffraction-limited storage ring with a regenerative amplifier free-electron laser (RAFEL) employing a transverse gradient undulator (TGU). By introducing dispersion in the storage ring, electrons of different energies are directed into corresponding magnetic field strengths of the TGU, thereby satisfying the resonance condition under a large energy spread and increasing the FEL gain. Simulations show that at equilibrium, the average EUV power exceeds 1 kW, with an output pulse energy reaching ∼2.86 μJ, while the energy spread stabilizes at ∼0.45%. These results demonstrate the feasibility of ring-based RAFEL with TGU as a promising route toward kilowatt-level EUV sources.