arXiv subjects

A. Longman

Publications and source records attributed to A. Longman.

10 recordsLinked to original sources

arXiv2026

Electron Injection and Beam Dynamics in a Laser Wakefield Acceleration Driven by Laser Pulses Carrying Orbital Angular Momentum

Laser pulses carrying orbital angular momentum (OAM) provide a new degree of freedom for controlling plasma-based accelerators. Here, we demonstrate experimentally laser wakefield acceler- ation driven by OAM laser pulses, producing electron beams with distinct broad-band energy spectra and angularly structured phase space. The measured spectra exhibit a two-beamlet structure with correlated angular dispersion, indicating injection occurring at multiple azimuthal phases of the plasma wake. Particle-in-cell simulations reproduced the observed spectral features and revealed helical electron trajectories driven by the OAM-induced wakefields. These results show that the phase structure of the laser driver can shape electron injection and acceleration dynamics, opening a route toward optimal control of beam structure in compact laser-driven accelerators.

physics.plasm-ph↗

arXiv2025

Pump with broadband probe experiments for single-shot measurements of plasma conditions and crossed-beam energy transfer

A novel technique for measuring plasma conditions using monochromatic pump-broadband probe laser interactions has been experimentally demonstrated. Originally proposed in [J. Ludwig et al., Phys. Plasmas \textbf{26}, 113108 (2019)], this method utilizes crossed-beam energy transfer between the broadband probe and the pump, mediated by plasma ion acoustic waves. The complete energy transfer spectrum can be captured in a single shot, enabling the inference of plasma parameters such as density, electron and ion temperatures, and flow velocity. Compared to Thomson scattering, this technique offers signal enhancements typically larger than 9 orders of magnitude, significantly reducing the required probe laser intensity and facilitating interactions that are linear and measurements that are non-perturbative of the plasma. Furthermore, it provides a powerful tool for advancing studies of crossed-beam energy transfer under conditions relevant to inertial confinement fusion experiments.

physics.plasm-ph↗

arXiv2023

Towards direct spatial and intensity characterization of ultra-high intensity laser pulses using ponderomotive scattering of free electrons

Spatial distributions of electrons ionized and scattered from ultra-low pressure gases are proposed and experimentally demonstrated as a method to directly measure the intensity of an ultra-high intensity laser pulse. Analytic models relating the peak scattered electron energy to the peak laser intensity are derived and compared to paraxial Runge-Kutta simulations highlighting two models suitable for describing electrons scattered from weakly paraxial beams ($f_{\#}>5$) for intensities in the range of $10^{18}-10^{21}$Wcm$^{-2}$. Scattering energies are shown to be dependant on gas species emphasizing the need for specific gases for given intensity ranges. Direct measurements of the laser intensity at full power of two laser systems is demonstrated both showing a good agreement between indirect methods of intensity measurement and the proposed method. One experiment exhibited the role of spatial aberrations in the scattered electron distribution motivating a qualitative study on the effect. We propose the use of convolutional neural networks as a method for extracting quantitative information of the spatial structure of the laser at full power. We believe the presented technique to be a powerful tool that can be immediately implemented in many high-power laser facilities worldwide.

physics.plasm-ph↗

arXiv2020

Generalized Analysis of the E\"{o}tv\"{o}s Experiment

We present a generalized phenomenological formalism for analyzing the original E\"{o}tv\"{o}s experiment in the presence of gravity and a generic "5th force." To date no evidence for a 5th force has emerged since its presence was suggested by a 1986 reanalysis of the 1922 publication coauthored by E\"{o}tv\"{o}s, Pek\`ar, and Fekete (EPF). However, our generalized analysis introduces new mechanisms capable in principle of accounting for the EPF data, while at the same time avoiding detection by most recent experiments carried out to date. As an example, some of these mechanisms raise the possibility that the EPF signal could have arisen from an unexpected direction if it originated from the motion of the Earth through a medium.

hep-ph↗

arXiv2019

Towards an in situ, full-power gauge of the focal-volume intensity of petawatt-class lasers

About 50 years ago, Sarachick and Schappert [Phys. Rev. D. 1, 2738 (1970)] showed that relativistic Thomson scattering leads to wavelength shifts that are proportional to the laser intensity. About 28 years later Chen et al. [Nature 396, 653 (1998)] used these shifts to estimate their laser intensity near 10^18 W/cm^2. More recently there have been several theoretical studies aimed at exploiting nonlinear Thomson scattering as a tool for direct measurement of intensities well into the relativistic regime. We present the first quantitative study of this approach for intensities between 10^18 and 10^19 W/cm^2. We show that the spectral shifts are in reasonable agreement with estimates of the peak intensity extracted from images of the focal area obtained at reduced power. Finally, we discuss the viability of the approach, its range of usefulness and how it might be extended to gauge intensities well in excess of 10^19 W/cm^2.

physics.plasm-ph↗

arXiv2018

Development of an adjustable Kirkpatrick-Baez microscope for laser driven x-ray sources at CLPU

A promising prototype of a highly adjustable Kirkpatrick-Baez (KB) microscope has been designed, built and tested in a number of laser driven x-ray experiments using the high power (200TW) VEGA-2 laser system of the Spanish Centre for Pulsed Lasers (CLPU). The presented KB version consists of two, perpendicularly mounted, 500{\mu}m thick Silicon wafers, coated with a few tens of nm layer of Platinum unlike the conventional, coated, millimetre thick glass substrates, affording more bending flexibility and large adjustment range. According to simulations, and based on total external reflection, this KB offers a broad-band multi-keV reflection spectra, allowing more spectral tunablity than conventional Bragg crystals. In addition to be vacuum compatible, the prototype is characterised by a relatively small size (21cm x 31cm x 27cm) and permits remote control and modification of both the radius of curvature (down to 10m) and the grazing incidence angle (up to 60mrad). A few examples of focusing performance tests, limitations and experimental campaign results are discussed.

physics.ins-det↗

arXiv2018

Generation of high energy laser-driven electron and proton sources with the 200 TW system VEGA 2 at the Centro de Laseres Pulsados

The Centro de Laseres Pulsados in Salamanca Spain has recently started operation phase and the first User access period on the 6 J 30 fs 200 TW system (VEGA 2) already started at the beginning of 2018. In this paper we report on two commissioning experiments recently performed on the VEGA 2 system in preparation for the user campaign. VEGA 2 system has been tested in different configurations depending on the focusing optics and targets used. One configuration (long focal length f=130 cm) is for under-dense laser-matter interaction where VEGA 2 is focused onto a low density gas-jet generating electron beams (via laser wake field acceleration mechanism) with maximum energy up to 500 MeV and an X-ray betatron source with a 10 keV critical energy. A second configuration (short focal length f=40 cm) is for over-dense laser-matter interaction where VEGA 2 is focused onto an 5 microns thick Al target generating a proton beam with a maximum energy of 10 MeV and average energy of 7-8 MeV and temperature of 2.5 MeV. In this paper we present preliminary experimental results.

physics.plasm-ph↗

arXiv2018

Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 $μ$m lasers

Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $μ$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.

physics.plasm-ph↗

arXiv2016

Is there a signal for Lorentz non-invariance in existing radioactive decay data?

Measurements of the beta decay rates of nuclei have revealed annual periodicities with approximately the same relative amplitude even though the half-lives range over nine orders of magnitude. Here we show that this can be explained if the emitted neutrinos behave as if they propagate in a medium with a refractive index which varies as the Earth orbits the sun. This refractive index may be due to fundamental Lorentz non-invariance (LNI), or apparent LNI arising from interactions with solar or relic neutrinos, or dark matter. Additionally, this medium could have consequences for experiments attempting to measure the neutrino mass.

hep-ph↗

arXiv2010

Power Spectrum Analyses of Nuclear Decay Rates

We provide the results from a spectral analysis of nuclear decay data displaying annually varying periodic fluctuations. The analyzed data were obtained from three distinct data sets: 32Si and 36Cl decays reported by an experiment performed at the Brookhaven National Laboratory (BNL), 56Mn decay reported by the Children's Nutrition Research Center (CNRC), but also performed at BNL, and 226Ra decay reported by an experiment performed at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. All three data sets exhibit the same primary frequency mode consisting of an annual period. Additional spectral comparisons of the data to local ambient temperature, atmospheric pressure, relative humidity, Earth-Sun distance, and their reciprocals were performed. No common phases were found between the factors investigated and those exhibited by the nuclear decay data. This suggests that either a combination of factors was responsible, or that, if it was a single factor, its effects on the decay rate experiments are not a direct synchronous modulation. We conclude that the annual periodicity in these data sets is a real effect, but that further study involving additional carefully controlled experiments will be needed to establish its origin.

nucl-ex↗