arXiv subjects

P. G. O'Shea

Publications and source records attributed to P. G. O'Shea.

5 recordsLinked to original sources

arXiv2026

An x-ray regenerative amplifier free-electron laser with a step-tapered-undulator

Regenerative amplifier x-ray free-electron lasers constitute alternative configurations for fourth generation light sources which are typically operated in self-amplified spontaneous emission (SASE) mode. However, SASE exhibits relatively large fluctuations in the power and spectral properties from shot to shot, whereas XRAFELs provide a much more stable source of hard x-ray photons. Here, we study the performance of an x-ray cavity under consideration at the Stanford Linear Accelerator Facility using both uniform and step-tapered undulators with either transmissive or hole out-coupling.

physics.acc-ph↗

arXiv2025

First Observation of Dispersive Shock Waves in an Electron Beam

Dispersive shock waves (DSWs) are expanding nonlinear wave trains that arise when dispersion regularizes a steepening front, a phenomenon observed in fluids, plasmas, optics, and superfluids. Here we report the first experimental observation of DSWs in an intense electron beam, using the University of Maryland Electron Ring (UMER). A localized induction-cell perturbation produced a negative density pulse that evolved into a leading soliton-like peak followed by an expanding train of oscillations. The leading peak satisfied soliton scaling laws for width^2 vs inverse amplitude and velocity vs amplitude, while the total wave-train width increased linearly with time, consistent with Korteweg--de Vries (KdV) predictions. Successive peaks showed decreasing amplitude and velocity toward the trailing edge, in agreement with dispersive shock ordering. These results demonstrate that intense charged particle beams provide a new laboratory platform for studying dispersive hydrodynamics, extending nonlinear wave physics into the high-intensity beam regime.

physics.acc-ph↗

arXiv2008

Multi-component measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation

High brightness electron accelerators, such as energy recovery linacs (ERL), often have complex particle distributions that can create difficulties in beam transport as well as matching to devices such as wigglers used to generate radiation from the beam. Optical transition radiation (OTR), OTR interferometry (OTRI) and optical diffraction-transition radiation interferometry (ODTRI) have proven to be effective tools for diagnosing both the spatial and angular distributions of charged particle beams. OTRI and ODTRI have been used to measure rms divergences and optical transverse phase space mapping has been demonstrated using OTRI. In this work we present the results of diagnostic experiments using OTR and ODR conducted at the Jefferson Laboratory 115 MeV ERL which show the presence of two separate components within the spatial and angular distributions of the beam. By assuming a correlation between the spatial and angular features we estimate an rms emittance value for each of the two components.

physics.acc-ph↗

arXiv2001

Optical Diffraction-Transition Radiation Interferometry and its Application to the Measurement of Beam Divergence

Optical transition radiation interferometry (OTRI) has been shown to be a very useful technique to measure the divergence of electron beams with energies in the range of 15-100 MeV. However, application of this method to low energy or very high quality beams is limited by scattering in the front foil of the interferometer. To overcome this limitation we propose to use a perforated front foil. For the beam energy and hole sizes we are considering, the unscattered beam electrons passing through the holes will produce diffraction radiation (ODR). The total radiation produced from the first and second foils then will be a spatially coherent sum of ODR and OTR from unscattered and scattered electrons. By controlling the number and size of the perforations, the inter-foil spacing, the thickness of the first foil and the wavelength and band pass of the observed radiation, the coherent interferences due to the unscattered portion of the beam can be isolated and observed. The visibility of these interferences can then be used to determine the rms beam divergence. We have developed a general computer code which can be used to calculate diffraction radiation from any type of perforation and another code to compute the ODR-OTR interference pattern for a given set of beam and optical parameters. These codes are employed in the design of an interferometer to measure the divergence of the ATF accelerator operating at 30 MeV. This beam will be used in an initial proof of principle experiment for the ODR-OTR interferometer. We present the results of our code calculations which show that the expected divergence, 200 micro radians, can be easily measured.

physics.acc-ph↗

arXiv2000

Energy Transfer Mechanisms and Equipartitioning in non-Equilibrium Space- Charge-Dominated Beams

A process of energy transfer is demonstrated in non-equilibrium charged particle beams with anisotropy and space charge. Equipartitioning of energy between available degrees of freedom occurs in just a few betatron wavelengths, without halo formation. Collective space charge modes similar to those observed in recent experiments provide the underlying coupling mechanism. Since laboratory beams are commonly far from equilibrium, the traditional K-V stability analysis does not necessarily apply, implying that selection of an operating point based on theory does not necessarily avoid equipartitioning. Furthermore, the rate of equipartitioning is shown to depend on a single free parameter related space charge content of the final (equipartitioned) beam, and does not depend on how the kinetic energy is initially distributed between the two planes.

physics.acc-ph↗