arXiv subjects

Michael Litos

Publications and source records attributed to Michael Litos.

8 recordsLinked to original sources

arXiv2026

Multi-GeV Electron Combs from a Plasma Wakefield Accelerator

Plasma accelerators now produce GeV-class electron beams with brightness and stability sufficient to drive free-electron lasers. Beyond this, they possess a unique yet largely unexplored capability: shaping the phase space of the beam in situ during injection, on femtosecond or shorter timescales. Here we demonstrate this capability by generating a multi-GeV electron comb comprising more than ten microbunches simultaneously separated in both energy and time. Periodic pinching of the drive beam inside its self-excited plasma wake sequentially injects microbunches via ionization of embedded helium atoms at successive betatron oscillations, while the gently varying plasma density maps each bunchlet to a distinct wake phase, compressing electrons trapped over a ~17 cm region into a comb only micrometers long. Individual microbunches exhibit percent-level energy spreads, energy spacing up to ten percent, and contain several picocoulomb charge. The percent-level spreads and parabolic energy-spacing trend provide experimental evidence for sub-femtosecond microbunch durations and few-femtosecond separations as revealed by beam-loading analysis and confirmed by particle-in-cell simulations. This work demonstrates femtosecond, in-situ phase-space shaping in plasma accelerators, paving the way for electron beams with tailored energy-time structure.

physics.acc-ph↗

arXiv2025

Three Dimensional Theory of the Ion Channel Laser

The ion channel laser (ICL) is a plasma-based alternative to the free electron laser (FEL) that uses the electric field of a uniform-density ion channel rather than the magnetic field of an undulator to induce transverse oscillations of electrons in an ultrarelativistic bunch and thereby produce coherent radiation via a collective electromagnetic instability. The powerful focusing of the ion channel generally yields significantly higher gain parameters in the ICL as compared to the FEL. This permits lasing in extremely short distances using electron bunches with an energy spread as large as a few percent; a value readily achievable with current plasma-based accelerators. ICLs, however, impose stringent transverse phase space requirements on the electron bunch beyond what is required in FELs. In this work, we present a novel 3D theory of the planar off-axis configuration of the ICL that accounts for a number of effects including diffraction, transverse radiation profile, frequency and betatron phase detuning, and nonzero spread in energy and undulator parameter. We derive the ICL pendulum and field equations, which we use to write down the 3D Maxwell-Klimontovich equations. After linearizing, we obtain an integro-differential equation describing the $z$-evolution of the radiation field. The 3D ICL dispersion relation is obtained using a Van Kampen normal mode expansion. We numerically solve the $z$-evolution equation to compute radiation power growth rates and transverse radiation profiles over a range of different ICL parameters. We examine the gain reduction due to 3D effects, energy spread, and emittance. Electron bunch phase space and emittance requirements for lasing are derived. Finally, we make general observations about the performance and feasibility of the ICL and discuss future prospects.

physics.acc-ph↗

arXiv2025

Precision alignment and tolerance of a plasma wakefield accelerator in a laser-ionized plasma source

We present a novel method for aligning a laser ionized plasma source to a pair of ultra-relativistic electron beams that comprise a plasma wakefield accelerator (PWFA). We achieve alignment by analyzing the plasma afterglow light observed at two longitudinal locations as the plasma column is scanned across the electron beam. By analyzing the relative plasma light intensity at the two locations, we aligned an 85-cm plasma source to a 10 GeV, 1.6 nC electron beam to within 10 um offset, 10 urad tilt. The alignment is verified by analyzing the drive beam energy loss, energy transfer efficiency, and the witness beam energy gain as a function of the misalignment between the beams and the plasma. From this measurement, we extract the alignment tolerance required between the laser-ionized plasma source and electron beams, an important metric necessary for collider design studies or light source applications based on a laser-ionized plasma source.

physics.acc-ph↗

arXiv2025

Design Initiative for a 10 TeV pCM Wakefield Collider

This document outlines a community-driven Design Study for a 10 TeV pCM Wakefield Accelerator Collider. The 2020 ESPP Report emphasized the need for Advanced Accelerator R\&D, and the 2023 P5 Report calls for the ``delivery of an end-to-end design concept, including cost scales, with self-consistent parameters throughout." This Design Study leverages recent experimental and theoretical progress resulting from a global R\&D program in order to deliver a unified, 10 TeV Wakefield Collider concept. Wakefield Accelerators provide ultra-high accelerating gradients which enables an upgrade path that will extend the reach of Linear Colliders beyond the electroweak scale. Here, we describe the organization of the Design Study including timeline and deliverables, and we detail the requirements and challenges on the path to a 10 TeV Wakefield Collider.

physics.acc-ph↗

arXiv2023

Temporal Evolution of the Light Emitted by a Thin, Laser-ionized Plasma Source

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized Helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell (PIC) code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source and this work is useful to understand the plasma light measurement, which plays an important role in the PWFA.

physics.plasm-ph↗

arXiv2023

Beam Delivery and Beamstrahlung Considerations for Ultra-High Energy Linear Colliders

As part of the Snowmass'21 community planning excercise, the Advanced Accelerator Concepts (AAC) community proposed future linear colliders with center-of-mass energies up to 15 TeV and luminosities up to 50$\times10^{34}$ cm$^{-2}$s$^{-1}$ in a compact footprint. In addition to being compact, these machines must also be energy efficient. We identify two challenges that must be addressed in the design of these machines. First, the Beam Delivery System (BDS) must not add significant length to the accelerator complex. Second, beam parameters must be chosen to mitigate beamstrahlung effects and maximize the luminosity-per-power of the machine. In this paper, we review advances in plasma lens technology that will help to reduce the length of the BDS system and we detail new Particle-in-Cell simulation studies that will provide insight into beamstrahlung mitigation techniques. We apply our analysis to both $e^+e^-$ and $\gamma\gamma$ colliders.

physics.acc-ph↗

arXiv2023

Acceleration of a Positron Bunch in a Hollow Channel Plasma

Plasmas are a compelling medium for particle acceleration owing to their natural ability to sustain electric fields that are orders of magnitude larger than those available in conventional radio-frequency accelerators. Plasmas are also unique amongst accelerator technologies in that they respond differently to beams of opposite charge. The asymmetric response of a plasma to highly-relativistic electron and positron beams arises from the fact that plasmas are composed of light, mobile electrons and heavy, stationary ions. Hollow channel plasma acceleration is a technique for symmetrizing the response of the plasma, such that it works equally well for high-energy electron and positron beams. In the experiment described here, we demonstrate the generation of a positron beam-driven wake in an extended, annular plasma channel, and acceleration of a second trailing witness positron bunch by the wake. The leading bunch excites the plasma wakefield and loses energy to the plasma, while the witness bunch experiences an accelerating field and gains energy, thus providing a proof-of-concept for hollow channel acceleration of positron beams. At a bunch separation of 330 um, the accelerating gradient is 70 MV/m, the transformer ratio is 0.55, and the energy transfer efficiency is 18% for a drive-to-witness beam charge ratio of 5:1.

physics.acc-ph↗

arXiv2022

C$^3$ Demonstration Research and Development Plan

C$^3$ is an opportunity to realize an e$^+$e$^-$ collider for the study of the Higgs boson at $\sqrt{s} = 250$ GeV, with a well defined upgrade path to 550 GeV while staying on the same short facility footprint. C$^3$ is based on a fundamentally new approach to normal conducting linear accelerators that achieves both high gradient and high efficiency at relatively low cost. Given the advanced state of linear collider designs, the key system that requires technical maturation for C$^3$ is the main linac. This white paper presents the staged approach towards a facility to demonstrate C$^3$ technology with both Direct (source and main linac) and Parallel (beam delivery, damping ring, ancillary component) R&D. The white paper also includes discussion on the approach for technology industrialization, related HEP R&D activities that are enabled by C$^3$ R&D, infrastructure requirements and siting options.

physics.acc-ph↗