arXiv subjects

Aaron Alejo

Publications and source records attributed to Aaron Alejo.

4 recordsLinked to original sources

arXiv2025

Enhancing Neutron Measurement Accuracy with Bubble Detectors at Laser-Driven Neutron Sources

Bubble detectors are widely used to measure neutron flux from laser-driven sources employing a pitcher-catcher setup, due to their insensitivity to intense $\gamma$-ray backgrounds and strong electromagnetic pulses (EMP).\\ This paper presents a method to account for the neutron energy-dependent response of bubble detectors, enabling accurate conversion of bubble counts into neutron flux at the detector location. The proposed method is based on the accurate reconstruction of the response function using a surrogate model. The resulting model is convoluted with the (normalized) expected/measured neutron spectrum to obtain an effective measure of the bubble detector's response, herein referred to as effective $c$ or $c_\text{eff}$. This effective value for the response is energy-independent after the convolution. In this way, our approach includes the spectral distribution of neutrons arriving at the detector to determine the integral neutron flux. Analyzing our experimental results obtained at the DRACO PW laser and comparing the results to previously used methods to obtain neutron fluxes from bubble detectors returns a reduction in neutron flux of up to \SI{31}{\%}. Results from the method detailed in this paper agree with in-depth experimental setup Monte Carlo simulations, with deviations of less than \SI{10}{\%}. We furthermore discuss the inherent limitations of our method with regard to its uncertainty and highlight the influence of neutron scattering in bubble detector measurements. For our experimental setup at the DRACO laser, up to \SI{47}{\%} of the detected neutrons arrive at the detector after undergoing at least one scattering event.

physics.ins-det↗

arXiv2021

Ultra-short, MeV-scale laser-plasma positron source for positron annihilation lifetime spectroscopy

Sub-micron defects represent a well-known fundamental problem in manufacturing since they can significantly affect performance and lifetime of virtually any high-value component. Positron annihilation lifetime spectroscopy is arguably the only established method capable of detecting defects down to the sub-nanometer scale but, to date, it only works for surface studies, and with limited resolution. Here, we experimentally and numerically show that laser-driven systems can overcome these well-known limitations, by generating ultra-short positron beams with a kinetic energy tuneable from 500 keV up to 2 MeV and a number of positrons per shot in a 50 keV energy slice \color{black} of the order of $10^3$. Numerical simulations of the expected performance of a typical mJ-scale kHz laser demonstrate the possibility of generating MeV-scale narrow-band and ultra-short positron beams with a flux exceeding $10^5$ positrons/s, of interest for fast volumetric scanning of materials at high resolution.

physics.acc-ph↗

arXiv2020

Non-invasive characterisation of a laser-driven positron beam

We report on an indirect and non-invasive method to simultaneously characterise the energy-dependent emittance and source size of ultra-relativistic positron beams generated during the propagation of a laser-wakefield accelerated electron beam through a high-Z converter target. The strong correlation of the geometrical emittance of the positrons with that of the scattered electrons allows the former to be inferred, with high accuracy, from monitoring the latter. The technique has been tested in a proof-of-principle experiment where, for 100 MeV positrons, we infer geometrical emittances and source sizes of the order of $ε_{e^+} \approx$ 3 $μ$m and $D_{e^+} \approx$ 150 $μ$m, respectively. This is consistent with the numerically predicted possibility of achieving sub-$μ$m geometrical emittances and micron-scale source sizes at the GeV level.

physics.plasm-ph↗

arXiv2018

Laser-driven high-quality positron sources as possible injectors for plasma-based accelerators

The intrinsic constraints in the amplitude of the accelerating fields sustainable by radio-frequency accelerators demand for the pursuit of alternative and more compact acceleration schemes. Among these, plasma-based accelerators are arguably the most promising, thanks to the high-accelerating fields they can sustain, greatly exceeding the GeV/m. While plasma-based acceleration of electrons is now sufficiently mature for systematic studies in this direction, positron acceleration is still at its infancy, with limited projects currently undergoing to provide a viable test facility for further experiments. In this article, we propose a recently demonstrated laser-driven configuration as a relatively compact and inexpensive source of high-quality ultra-relativistic positrons for laser-driven and particle-driven plasma wakefield acceleration studies. Monte-Carlo simulations show that near-term high-intensity laser facilities can produce positron beams with high-current, femtosecond-scale duration, and sufficiently low normalised emittance at energies in the GeV range to be injected in further acceleration stages.

physics.plasm-ph↗