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 $2.3\times {10}^{24}\mathrm{photons}{\mathrm{s}}^{-1}{\mathrm{mm}}^{-2}{\mathrm{mrad}}^{-2}$ ${(0.1\%\mathrm{bandwidth})}^{-1}$.

Generation of coherent radiation pulses is of remarkable interest in the synchrotron light source community. A novel technique has been proposed to produce temporal coherent radiation in ref. [1]. In this scheme, an oblique incidence seed laser is utilized to introduce an angular modulation which is converted to microbunching by an angular dispersion section. In this paper, a specific design of the angular dispersion section is given to realize the coupling between transverse and longitudinal directions which satisfied the microbunching requirements of this technique. Numerical simulation results demonstrate that this lattice can be used to enhance the bunching factor at very high harmonics of the seed laser. The lattice structure has good flexibility, the elements of the transport matrix related to microbunching can be easily adjusted, and the beta function in the radiator can be simply optimized by adjusting the magnets of the transport line.

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.