Searcharxiv⌕ Search

arXiv subjects

Xiujie Deng

Publications and source records attributed to Xiujie Deng.

12 recordsLinked to original sources
arXiv2026

Weak-Strong Steady-State Microbunching Accelerator Light Source

We propose a phase space manipulation involving one energy modulation sandwiched by two dispersion sections which converts a bunched particle beam or bunch train to ultra-high-harmonic density modulation, while the energy modulation in principle can be arbitrarily weak. The same scheme can also be used for energy bunching, creating energy levels in a bunched beam. We further propose a mechanism invoking three laser modulators in a storage ring to longitudinally focus the electron beam both weakly and strongly, such that a microbunch train and its high-density-harmonics or energy bunching form and sustain turn-by-turn. We call this mechanism weak-strong steady-state microbunching (Weak-Strong SSMB). The longitudinal beta function can vary by seven orders of magnitude along such a ring, with the minimal value squeezed to 10 nm. An example application of Weak-Strong SSMB for kW coherent EUV radiation is presented. Extension to X-ray can be anticipated. An energy-leveled electron beam enables $γ$-ray frequency comb production. The ideas can be scaled to wavelengths like RF and THz, for bunch length and energy spread control, ultrashort X-ray and coherent THz generation. Our work establishes a new paradigm for longitudinal dynamics study, accelerator light source development, and opens great potential for accelerator physics and technology.

physics.acc-ph↗
arXiv2026

Echo Enhanced Strong Focusing for Coherent Short-Wavelength Radiation

Storage-ring-based fully coherent light sources, including steady-state microbunching (SSMB), as well as compact seeded FELs driven by laser plasma accelerators, typically have relatively large intrinsic energy spreads. Extending the spectral reach of these facilities toward the X-ray regime represents a major challenge, as existing seeded schemes require rather extreme parameters to generate appreciable microbunching at high harmonics. In this Letter, we propose an echo enhanced strong focusing scheme that employs transverse-longitudinal coupling together with the beam echo effect to simultaneously resolve the energy spread bottleneck and enable efficient high-harmonic generation. This approach substantially relaxes the requirements on both the intrinsic energy spread and the transverse emittance, paving the way for soft X-ray production using relatively weak laser modulation. Based on this scheme, we further present an SSMB storage ring capable of generating kW-level average power 6.7 nm soft X-ray radiation.

physics.acc-ph↗
arXiv2026

Longitudinal beam instability driven by coherent radiation in an SSMB laser modulator

Storage ring-based steady-state microbunching (SSMB) is a promising approach for generating high-average-power coherent radiation, while the instabilities driven by coherent undulator radiation in the laser modulator (LM) is important for the ring performance. In this paper we investigate the longitudinal single-bunch multi-turn LM instability using cavity mode decomposition techniques. The evolution of the wakefield in the longitudinal beam dynamics equations are derived, and the instability growth rates are analyzed. Numerical simulations show excellent agreement with the theoretical model, validating the mode decomposition approach. These findings provide critical insights into the design and operation of SSMB storage rings, suggesting effective mitigation strategies to suppress the instability and enhance the overall performance.

physics.acc-ph↗
arXiv2025

Stochastic Cooling Enhanced Steady-State Microbunching

In this paper, we propose to combine two promising research topics in accelerator physics, i.e., optical stochastic cooling (OSC) and steady-state microbunching (SSMB). Our study shows that such an OSC-SSMB storage ring with a circumference of 50 m and beam energy of several hundred MeVs using present technology can deliver kilowatt radiation at 100 nm wavelength. A more ambitious application of OSC in an SSMB ring can push the radiation wavelength to an even shorter wavelength, such as EUV and soft X-ray. Such a powerful compact light source could benefit fundamental science research and industry applications.

physics.acc-ph↗
arXiv2025

Spectral Form Function with Applications in Beam Physics

To describe longitudinal fine structure like microbunching within a particle beam, a classical approach is to define a bunching factor which is the Fourier transform of the particle longitudinal density distribution. Such a 1D definition of bunching factor can be generalized to a 6D spectral form function (SFF) to describe more complicated structure in phase space. The complex SFF is another complete description of beam in spectral domain and can offer complementary and valuable insight in beam dynamics study which usually invokes the real particle density distribution. The basic property and Fokker-Planck equation of the SFF is presented, along with its solution in a general coupled linear lattice. The example applications of SFF in electron storage ring physics and laser-induced microbunching are presented.

physics.acc-ph↗
arXiv2024

Steady-State Micro-Bunching based on Transverse-Longitudinal Coupling

In this paper, three specific scenarios of a novel accelerator light source mechanism called steady-state micro-bunching (SSMB) have been studied, i.e., longitudinal weak focusing, longitudinal strong focusing and generalized longitudinal strong focusing (GLSF). At present, GLSF is the most promising among them in realizing high-power short-wavelength coherent radiation with a mild requirement on the modulation laser power. Its essence is to exploit the ultrasmall natural vertical emittance of an electron beam in a planar storage ring for efficient microbunching formation, like a partial transverse-longitudinal emittance exchange at the optical laser wavelength range. Based on indepth investigation of related beam physics, a solution of a GLSF SSMB storage ring which can deliver 1 kW-average-power EUV light is presented. The work in this paper, such as the generalized Courant-Snyder formalism, the analysis of theoretical minimum emittances, transverse-longitudinal coupling dynamics, and the derivation of bunching factor and modulation strengths for laser-induced microbunching schemes, is expected to be useful not only for the development of SSMB but also for future accelerator light sources in general that demand increasingly precise electron beam phase space manipulations.

physics.acc-ph↗
arXiv2024

Contribution of Wiggler to Radiation Integral in an Electron Storage Ring

With the advancement of accelerator light sources, the application of wiggler becomes more and more important, for example to speed up damping or generate synchrotron radiation. The quantum excitation contribution of such a wiggler to the electron beam emittance in a storage ring should be carefully evaluated when small emittance is desired. What found in literature is an approximate formula. Here we present a more exact result, which is of value for future light source development.

physics.acc-ph↗
arXiv2024

Application of Optical Stochastic Cooling in Future Accelerator Light Sources

In this paper, we propose to combine two promising research topics in accelerator physics, i.e., optical stochastic cooling (OSC) and steady-state microbunching (SSMB). The motivation is to provide a powerful radiation source which could benefit fundamental science research and industry applications. Our study shows that such a compact OSC-SSMB storage ring using present technology can deliver EUV light with an average power of kilowatt, and spectral flux $>10^{20}$ phs/s/0.1\%b.w., which is four orders of magnitude higher than existing synchrotron sources. It is expected that the presented work is of value for the development of both OSC and SSMB.

physics.acc-ph↗
arXiv2024

Instantaneous and Retarded Interactions in Coherent Radiation

In coherent radiation of an ensemble of electrons, radiation field from electrons resonantly drives the other electrons inside to produce stimulated emission. The radiation reaction force on the electrons accounting for this stimulated radiation loss is classically described by the Lienard-Wiechert potential. Despite its being the foundation of beam physics for decades, we show that using the "acceleration field'' in Lienard-Wiechert potential to describe radiative interactions leads to divergences due to its implicit dependence on instantaneous interactions. Here, we propose an alternative theory for electromagnetic radiation by decomposing the interactions into instantaneous part and retarded part. It is shown that only the retarded part contributes to the irreversible radiation loss and the instantaneous part describes the space charge related effects. We further apply this theory to study the coherent synchrotron radiation wake, which hopefully will reshape our understanding of coherent radiation and collective interactions.

physics.acc-ph↗
arXiv2023

Theorems on Transverse-Longitudinal Coupling-Based Bunch Compression and Harmonic Generation Schemes

In particle accelerators, transverse-longitudinal coupling (TLC) dynamics can be invoked for efficient bunch compression or high harmonic generation when one of the transverse eigenemittance is small. In this sense, complete or partial transverse-to-longitudinal emittance exchange in optical wavelength range is being actively studied, for example in free-electron lasers. Another example is the recent work on generalized longitudinal strong focusing steady-state microbunching, where TLC is exploited to take advantage of the ultrasmall vertical emittance in a planar electron storage ring to lower the modulation laser power for ultrashort microbunch generation on a turn-by-turn basis. For this kind of schemes, we have proved before three theorems, invoking 4D phase space dynamics, with their implications discussed. Here we generalize the analysis to 6D phase space dynamics. Various TLC-based beam manipulation scenarios, as listed in the references, are dictated by these theorems.

physics.acc-ph↗
arXiv2022

Theoretical and Experimental Studies on Steady-state Microbunching

Particle accelerators as photon sources are advanced tools in studying the structure and dynamical properties of matter. The present workhorses of these sources are storage ring-based synchrotron radiation facilities and linear accelerator-based free-electron lasers, delivering light with high repetition rate and high peak brilliance (power), respectively. The steady-state microbunching (SSMB) mechanism was proposed to bridge the gap of these two kinds of sources to generate high-average-power, high-repetition-rate coherent radiation in an electron storage ring. Such a novel light source promises new possibilities for accelerator photon science and industry applications, for example in ultra-high-energy-resolution angle-resolved photoemission spectroscopy and extreme ultraviolet lithography. The six orders of magnitude extrapolation of the electron bunch length in an SSMB storage ring compared to that of a conventional ring provides tremendous opportunities for accelerator physics research. This dissertation is devoted to the theoretical and experimental investigations of SSMB, with important results achieved. The work presented can be summarized as: first, how to realize SSMB; second, what radiation characteristics can we obtain from the formed SSMB; and third, experimentally demonstrate the working mechanism of SSMB in a real machine.

physics.acc-ph↗