In the underdense, or blowout regime, of plasma wakefield acceleration, the particle beam is denser than the plasma. In this scenario, the plasma electrons are nearly completely rarefied from the beam channel, leaving only a nominally uniform ion-filled "bubble." Extensive investigations of this interaction assuming axisymmetry have been undertaken. However, the blowout produced by a transversely asymmetric (flat) driver, which would be present in linear collider "afterburner" schemes, possesses quite different characteristics. Such beams create an asymmetric plasma bubble which leads to unequal focusing in the two transverse dimensions, accompanied by a nonuniform accelerating gradient. The asymmetric blowout cross section is found through simulation to be elliptical, and treating it as such permits a simple extension of the symmetric theory. In particular, focusing fields linear in both transverse directions inside the bubble are found. The form of the wake potential and the associated beam-matching conditions in this elliptical cavity are discussed. We also examine blowout boundary estimation in the long driver limit and applications of the salient asymmetric features of the wakefield.

Field electron emission, or electron tunneling through a potential energy (PE) barrier under the influence of a strong electrostatic (ES) or radio frequency (RF) field, is of broad interest to the accelerator physics community. For example, it is the source of undesirable dark currents in resonant cavities, providing a limit to high-field operation. Field electron emission can also be applied to quasi-statically model electron emission induced by the electric field in a laser pulse. The classical approach to field electron emission is the Fowler–Nordheim (FN) framework, which incorporates a simplified PE profile and various assumptions. Here, we build a more realistic model using the PE and charge densities derived from a density-functional theory (DFT) calculation. We examine the correction factors associated with each model assumption. Compared to the FN framework, our results can be extended up to 80 GV/m, a limit that has been reached in laser-induced strong field emission scenarios.

Electron rescattering has been well studied and simulated for cases with ponderomotive energies of the quasi-free electrons, derived from laser–gas and laser–surface interactions, lower than 50 eV. However, with advents in longer wavelengths and laser field enhancement metallic surfaces, previous simulations no longer suffice to describe more recent strong field and high yield experiments. We present a brief introduction to and some of the theoretical and empirical background of electron rescattering emissions from a metal. We set upon using the Jellium potential with a shielded atomic surface potential to model the metal. We then explore how the electron energy spectra are obtained in the quantum simulation, which is performed using a custom computationally intensive time-dependent Schrödinger equation solver via the Crank–Nicolson method. Finally, we discuss the results of the simulation and examine the effects of the incident laser’s wavelength, peak electric field strength, and field penetration on electron spectra and yields. Future simulations will investigate a more accurate density functional theory metallic model with a system of several non-interacting electrons. Eventually, we will move to a full time-dependent density functional theory approach.

Gas-filled waveguides enable few-cycle, spatio-temporally coupled (STC) pulses with programmable structure, opening new routes to control charged particles with optical fields. This review maps the landscape of optical-field-driven photoemission, then surveys gas-based nonlinear drivers, photonic crystal fibers (PCFs) for low-energy, high-repetition operation, and hollow-core capillaries (HCCs) for high-power, few-cycle synthesis. We highlight mechanisms for deterministic pulse shaping, including four-wave-mixing-based spectral-phase transfer in HCCs, and show how tailored STC waveforms steer emission dynamics from the multiphoton to tunneling regimes, enabling sub-cycle gating, momentum control, and brightness scaling. We conclude with open challenges: phase stability, mid-IR scalability, coupling to nanophotonic emitters, metrology of vectorial fields, and outline a path toward compact, ultrafast, phase-coherent electron sources and emerging quantum applications powered by nonlinear photonics.

A fundamental comparison between a magnetic undulator and an ion channel, or betatron, radiation from relativistic electrons is presented. While conventional theories nominally range from the undulator ( K < 1 ) to the wiggler ( K > 1 ) regime, they are only applicable for sufficiently large Lorentz factors ( γ 0 ≫ K ). They therefore do not account for high K / γ 0 cases, for which we show that particle trajectories and radiation characteristics strongly deviate from the linear predictions in both magnetic undulators and ion channels. This problem arises from the fundamental differences between a magnetostatically and electrostatically induced oscillation. A reformulation of both the ion channel betatron wavelength and amplitude, as well as the same parameters in a magnetic undulator, permits us to compare cases with equivalent oscillation period and amplitude in the two different scenarios. The notable differences in spectral features of the two radiation mechanisms can then be addressed via numerical simulations of single particle as well as full beam dynamics. Additionally, we identify and quantify a novel transverse orbit precession effect in ion channels for particles with initial angular momentum relative to the device axis. This effect, which is significant in cases of strong transverse kinetic energy oscillations, alters both the radiation divergence and the beam emittance. In this paper, we present this new theoretical framework and compare its results with numerical simulation applied to realizable experimental tests of such radiation sources.