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1. Fully plasma-based electron injector for a linear collider or XFEL

   https://doi.org/10.1103/PhysRevResearch.7.023118  

   Dalichaouch, T N; Xu, X L; Li, F; Tsung, F S; Mori, W B (May 2025, Physical Review Research)

   We demonstrate through high-fidelity particle-in-cell (PIC) simulations a simple approach for efficiently generating $20+$GeV electron beams with the necessary charge, energy spread, and emittance for use as an injector in a future linear collider or a next generation XFEL. A high quality injected bunch is generated by self-focusing an unmatched electron driver in a nonlinear plasma wakefield. Over pump depletion distances, the drive beam dynamics and self-loading effects lead to high energy, low-energy spread output beams. For plasma densities of ${10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$, PIC simulation results indicate that self-injected beams with $0.52\mathrm{n}\mathrm{C}$charge can be accelerated to 20 GeV with projected core energy spreads of $\lesssim 1\%$, normalized slice emittances of $110\mathrm{n}\mathrm{m}$, peak normalized brightness of $\gtrsim {10}^{19}\mathrm{A}/{\mathrm{m}}^2/{\mathrm{rad}}^2$, and transfer efficiencies of $\gtrsim 44\%$. 

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2. Dephasingless laser wakefield acceleration in the bubble regime

   https://doi.org/10.1038/s41598-023-48249-4  

   Miller, Kyle G.; Pierce, Jacob R.; Ambat, Manfred V.; Shaw, Jessica L.; Weichman, Kale; Mori, Warren B.; Froula, Dustin H.; Palastro, John P. (December 2023, Scientific Reports)

   Abstract Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space–time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space–time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse. 

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3. A Scalable, High-Efficiency, Low-Energy-Spread Laser Wakefield Accelerator Using a Tri-Plateau Plasma Channel

   https://doi.org/10.34133/research.0396  

   Liu, Shuang; Li, Fei; Zhou, Shiyu; Hua, Jianfei; Mori, Warren B; Joshi, Chan; Lu, Wei (January 2024, Research)

   The emergence of multi-petawatt laser facilities is expected to push forward the maximum energy gain that can be achieved in a single stage of a laser wakefield acceleration (LWFA) to tens of giga-electron volts, which begs the question—is it likely to impact particle physics by providing a truly compact particle collider? Colliders have very stringent requirements on beam energy, acceleration efficiency, and beam quality. In this article, we propose an LWFA scheme that can for the first time simultaneously achieve hitherto unrealized acceleration efficiency from the laser to the electron beam of >20% and a sub-1% energy spread using a stepwise plasma structure and a nonlinearly chirped laser pulse. Three-dimensional high-fidelity simulations show that the nonlinear chirp can effectively mitigate the laser waveform distortion and lengthen the acceleration distance. This, combined with an interstage rephasing process in the stepwise plasma, can triple the beam energy gain compared to that in a uniform plasma for a fixed laser energy, thereby dramatically increasing the efficiency. A dynamic beam loading effect can almost perfectly cancel the energy chirp that arises during the acceleration, leading to the sub-percent energy spread. This scheme is highly scalable and can be applied to petawatt LWFA scenarios. Scaling laws are obtained, which suggest that electron beams with parameters relevant for a Higgs factory could be reached with the proposed high-efficiency, low-energy-spread scheme. 

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4. A Laser Frequency Transverse Modulation Might Compensate for the Spectral Broadening Due to Large Electron Energy Spread in Thomson Sources

   https://doi.org/10.3390/photonics9020062  

   Petrillo, Vittoria; Drebot, Illya; Krafft, Geoffrey; Maroli, Cesare; Rossi, Andrea R.; Rossetti Conti, Marcello Rossetti; Ruijter, Marcel; Terzić, Balša (February 2022, Photonics)

   Compact laser plasma accelerators generate high-energy electron beams with increasing quality. When used in inverse Compton backscattering, however, the relatively large electron energy spread jeopardizes potential applications requiring small bandwidths. We present here a novel interaction scheme that allows us to compensate for the negative effects of the electron energy spread on the spectrum, by introducing a transverse spatial frequency modulation in the laser pulse. Such a laser chirp, together with a properly dispersed electron beam, can substantially reduce the broadening of the Compton bandwidth due to the electron energy spread. We show theoretical analysis and numerical simulations for hard X-ray Thomson sources based on laser plasma accelerators. 

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5. Generation of ultrahigh-brightness pre-bunched beams from a plasma cathode for X-ray free-electron lasers

   https://doi.org/10.1038/s41467-022-30806-6  

   Xu, Xinlu; Li, Fei; Tsung, Frank S.; Miller, Kyle; Yakimenko, Vitaly; Hogan, Mark J.; Joshi, Chan; Mori, Warren B. (December 2022, Nature Communications)

   Abstract The longitudinal coherence of X-ray free-electron lasers (XFELs) in the self-amplified spontaneous emission regime could be substantially improved if the high brightness electron beam could be pre-bunched on the radiated wavelength-scale. Here, we show that it is indeed possible to realize such current modulated electron beam at angstrom scale by exciting a nonlinear wake across a periodically modulated plasma-density downramp/plasma cathode. The density modulation turns on and off the injection of electrons in the wake while downramp provides a unique longitudinal mapping between the electrons’ initial injection positions and their final trapped positions inside the wake. The combined use of a downramp and periodic modulation of micrometers is shown to be able to produces a train of high peak current (17 kA) electron bunches with a modulation wavelength of 10’s of angstroms - orders of magnitude shorter than the plasma density modulation. The peak brightness of the nano-bunched beam can be O (10 21 A/m 2 /rad 2 ) orders of magnitude higher than current XFEL beams. Such prebunched, high brightness electron beams hold the promise for compact and lower cost XEFLs that can produce nanometer radiation with hundreds of GW power in a 10 s of centimeter long undulator. 

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