arXiv subjects

J. M. Garland

Publications and source records attributed to J. M. Garland.

12 recordsLinked to original sources

arXiv2026

Slice Emittance Preservation and Focus Control in a Passive Plasma Lens

Strong, symmetrically focusing plasma lenses are promising for accommodating the small beams associated with plasma-based accelerators and collider final foci. However, while focusing with active and passive plasma lenses has been experimentally demonstrated, compatibility with high-brightness beams relevant for applications has not. In this work, we show experimentally that passive plasma lenses can preserve free-electron-laser-quality slice emittance while focusing two orders of magnitude more strongly than quadrupole magnets, and that the focal parameters can be controlled.

physics.acc-ph↗

arXiv2025

Plasma lens for focusing attosecond pulses

Attosecond pulses provide unique opportunities for studies of time-resolved electron dynamics. However, focusing these pulses, typically ranging from the vacuum ultraviolet to the soft-X-ray region, remains challenging. Conventional refractive lenses are not suitable owing to the large dispersion and the strong absorption, while reflective optics, despite avoiding these issues, still lead to high losses. Here we propose a tunable plasma lens capable of focusing attosecond pulses, and experimentally demonstrate focusing of these pulses at extreme-ultraviolet photon energies around 20 eV and 80 eV. A key advantage is its compatibility with nonlinear frequency conversion processes like high-harmonic generation. The different focusing properties of the fundamental light and the generated harmonic frequencies allow for efficient separation of these components. Consequently, the transmission of high-harmonic generation beamlines can be increased to more than 80%, making this approach highly suitable for photon-demanding applications.

physics.optics↗

arXiv2025

Characterization of discharge capillaries via benchmarked hydrodynamic plasma simulations

Plasma accelerators utilize strong electric fields in plasma waves to accelerate charged particles, making them a compact alternative to radiofrequency technologies. Discharge capillaries are plasma sources used in plasma accelerator research to provide acceleration targets, or as plasma lenses to capture or focus accelerated beams. They have applications for beam-driven and laser-driven plasma accelerators and can sustain high repetition rates for extended periods of time. Despite these advantages, high-fidelity simulations of discharge capillaries remain challenging due to the range of mechanisms involved and the difficulty to diagnose them in experiments. In this work, we utilize hydrodynamic plasma simulations to examine the discharge process of a plasma cell and discuss implications for future accelerator systems. The simulation model is validated with experimental measurements in a 50-mm-long, 1-mm-wide plasma capillary operating a 12-27 kV discharge at 2-12mbar hydrogen pressure. For 20 kV at 8.7mbar the discharge is shown to deposit 178mJ of energy in the plasma. Potential difficulties with the common density measurement method using Hα emission spectroscopy are discussed. This simulation model enables investigations of repeatability, heat flow management and fine tailoring of the plasma profile with discharges.

physics.plasm-ph↗

arXiv2024

Energy Depletion and Re-Acceleration of Driver Electrons in a Plasma-Wakefield Accelerator

For plasma-wakefield accelerators to fulfil their potential for cost effectiveness, it is essential that their energy-transfer efficiency be maximized. A key aspect of this efficiency is the near-complete transfer of energy, or depletion, from the driver electrons to the plasma wake. Achieving full depletion is limited by the process of re-acceleration, which occurs when the driver electrons decelerate to non-relativistic energies, slipping backwards into the accelerating phase of the wakefield and being subsequently re-accelerated. Such re-acceleration is unambiguously observed here for the first time. At this re-acceleration limit, we measure a beam driver depositing (57 $\pm$ 3)\% of its energy into a 195-mm-long plasma. Combining this driver-to-plasma efficiency with previously measured plasma-to-beam and expected wall-plug-to-driver efficiencies, our result suggests that plasma-wakefield accelerators can in principle reach or even exceed the energy-transfer efficiency of conventional accelerators.

physics.acc-ph↗

arXiv2024

Emittance preservation in a plasma-wakefield accelerator

Radio-frequency particle accelerators are engines of discovery, powering high-energy physics and photon science, but are also large and expensive due to their limited accelerating fields. Plasma-wakefield accelerators (PWFAs) provide orders-of-magnitude stronger fields in the charge-density wave behind a particle bunch travelling in a plasma, promising particle accelerators of greatly reduced size and cost. However, PWFAs can easily degrade the beam quality of the bunches they accelerate. Emittance, which determines how tightly beams can be focused, is a critical beam quality in for instance colliders and free-electron lasers, but is particularly prone to degradation. We demonstrate, for the first time, emittance preservation in a high-gradient and high-efficiency PWFA while simultaneously preserving charge and energy spread. This establishes that PWFAs can accelerate without degradation$\unicode{x2014}$essential for energy boosters in photon science and multistage facilities for compact high-energy particle colliders.

physics.acc-ph↗

arXiv2022

Longitudinally resolved measurement of energy-transfer efficiency in a plasma-wakefield accelerator

Energy-transfer efficiency is an important quantity in plasma-wakefield acceleration, especially for applications that demand high average power. Conventionally, the efficiency is measured using an electron spectrometer; an invasive method that provides an energy-transfer efficiency averaged over the full length of the plasma accelerator. Here, we experimentally demonstrate a novel diagnostic utilizing the excess light emitted by the plasma after a beam-plasma interaction, which yields noninvasive, longitudinally resolved measurements of the local energy-transfer efficiency from the wake to the accelerated bunch; here, as high as (58 $\pm$ 3)%. This method is suitable for online optimization of individual stages in a future multistage plasma accelerator, and enables experimental studies of the relation between efficiency and transverse instability in the acceleration process.

physics.acc-ph↗

arXiv2021

Progress of the FLASHForward X-2 high-beam-quality, high-efficiency plasma-accelerator experiment

FLASHForward is an experimental facility at DESY dedicated to beam-driven plasma-accelerator research. The X-2 experiment aims to demonstrate acceleration with simultaneous beam-quality preservation and high energy efficiency in a compact plasma stage. We report on the completed commissioning, first experimental results, ongoing research topics, as well as plans for future upgrades.

physics.acc-ph↗

arXiv2020

Evolution of longitudinal plasma-density profiles in discharge capillaries for plasma wakefield accelerators

Precise characterization and tailoring of the spatial and temporal evolution of plasma density within plasma sources is critical for realizing high-quality accelerated beams in plasma wakefield accelerators. The simultaneous use of two independent diagnostic techniques allowed the temporally and spatially resolved detection of plasma density with unprecedented sensitivity and enabled the characterization of the plasma temperature at local thermodynamic equilibrium in discharge capillaries. A common-path two-color laser interferometer for obtaining the average plasma density with a sensitivity of $2\times 10^{15}$ cm$^{-2}$ was developed together with a plasma emission spectrometer for analyzing spectral line broadening profiles with a resolution of $5\times 10^{15}$ cm$^{-3}$. Both diagnostics show good agreement when applying the spectral line broadening analysis methodology of Gigosos and Carde{ñ}oso. Measured longitudinally resolved plasma density profiles exhibit a clear temporal evolution from an initial flat-top to a Gaussian-like shape in the first microseconds as material is ejected out from the capillary, deviating from the often-desired flat-top profile. For plasma with densities of 0.5-$2.5\times 10^{17}$ cm$^{-3}$, temperatures of 1-7 eV were indirectly measured. These measurements pave the way for highly detailed parameter tuning in plasma sources for particle accelerators and beam optics.

physics.plasm-ph↗

arXiv2018

Racetrack FFAG muon decay ring for nuSTORM with triplet focusing

The neutrino beam produced from muons decaying in a storage ring would be an ideal tool for precise neutrino cross section measurements and the search for sterile neutrinos due to its precisely known flavour content and spectrum. In the proposed nuSTORM facility, pions would be directly injected into a racetrack storage ring, where the circulating muon beam would be captured. In this paper we show that a muon decay ring based on a racetrack scaling FFAG (Fixed Field Alternating Gradient) with triplet focusing structures is a very promising option with potential advantages over the FODO based solution. We discuss the ring concept, machine parameters, linear optics design, beam dynamics and the injection system.

physics.acc-ph↗

arXiv2018

nuSTORM FFAG Decay Ring

The neutrino beam produced from muons decaying in a storage ring would be an ideal tool for precise neutrino cross section measurements and search for sterile neutrinos due to its precisely known flavour content and spectrum. In the proposed nuSTORM facility pions would be directly injected into a racetrack storage ring, where circulating muon beam would be captured. The storage ring has two options: a FODO solution with large aperture quadrupoles and a racetrack FFAG (Fixed Field Alternating Gradient) using the recent developments in FFAGs. Machine parameters, linear optics design and beam dynamics are discussed in this paper.

physics.acc-ph↗

arXiv2017

Medical therapy and imaging fixed-field alternating-gradient accelerator with realistic magnets

NORMA is a design for a normal-conducting race track fixed-field alternating-gradient accelerator (FFAG) for protons from 50 to 350 MeV. In this article we show the development from an idealised lattice to a design implemented with field maps from rigorous two-dimensional (2D) and three-dimensional (3D) FEM magnet modelling. We show that whilst the fields from a 2D model may reproduce the idealised field to a close approximation, adjustments must be made to the lattice to account for differences brought about by the 3D model and fringe fields and full 3D models. Implementing these lattice corrections we recover the required properties of small tune shift with energy and a sufficiently-large dynamic aperture. The main result is an iterative design method to produce the first realistic design for a proton therapy accelerator that can rapidly deliver protons for both treatment and for imaging at up to 350 MeV. The first iteration is performed explicitly and described in detail in the text.

physics.acc-ph↗

arXiv2016

Amplitude dependent orbital period in alternating gradient accelerators

Orbital period in a ring accelerator and time of flight in a linear accelerator depend on the amplitude of betatron oscillations. The variation is negligible in ordinary particle accelerators with relatively small beam emittance. In an accelerator for large emittance beams like muons and unstable nuclei, however, this effect cannot be ignored. We measured orbital period in a linear non-scaling fixed field alternating gradient (FFAG) accelerator, which is a candidate for muon acceleration, and compared with the theoretical prediction. The good agreement between them gives important ground for the design of particle accelerators for a new generation of particle and nuclear physics experiments.

physics.acc-ph↗