Abstract
Similarly to laser or x-ray beams, the interaction of sufficiently intense particle beams with neutral gases will result in the creation of plasma. In contrast to photon-based ionization, the strong unipolar field of a particle beam can generate a plasma where the electron population receives a large initial momentum kick and escapes, leaving behind unshielded ions. Measuring the properties of the ensuing Coulomb exploding ions—such as their kinetic energy distribution, yield, and spatial distribution—can provide information about the peak electric fields that are achieved in the electron beams. Particle-in-cell simulations and analytical models are presented for high-brightness electron beams of a few femtoseconds or even hundreds of attoseconds, and transverse beam sizes on the micron scale, as generated by today’s free electron lasers. Different density regimes for the utilization as a potential diagnostics are explored, and the fundamental differences in plasma dynamical behavior for e-beam or photon-based ionization are highlighted. By measuring the dynamics of field-induced ions for different gas and beam densities, a lower bound on the beam charge density can be obtained in a single shot and in a noninvasive way. The exponential dependency of the ionization yield on the beam properties can provide unprecedented spatial and temporal resolution, at the submicrometer and subfemtosecond scales, respectively, offering a practical and powerful approach to characterizing beams from accelerators at the frontiers of performance.
- Received 15 December 2017
- Revised 22 March 2018
DOI:https://doi.org/10.1103/PhysRevX.8.021039
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Advanced particle-accelerator-based facilities, such as free electron lasers or particle colliders, rely on high-brightness electron beams. While particle colliders are at the forefront of understanding the subatomic world, free electron lasers can image single molecules and track time-evolving processes with attosecond to femtosecond resolution. Future generations of accelerators will require even higher-brightness electron beams, and thus novel diagnostic devices are essential for characterization as well as control. Here, we propose a new way to measure the charge density of a high-brightness electron beam in a minimally invasive way using strong electric fields (tens of GV/m) associated with those beams.
These electric fields are strong enough to ionize a neutral gas through which the beam propagates. Via numerical simulations, we show that by analyzing the resulting plasma—such as its total ion yield, kinetic energy distribution, or even spatial distribution—we can extract information on the spatiotemporal distribution of the electron beam. Specifically, we show that a lower bound on the electron beam’s charge density can be extracted on a single-shot basis.
Our proposed method has the potential to characterize micrometer-sized electron beams with nanometer spatial resolution and subfemtosecond temporal resolution.
