arXiv subjects

Aidan Crilly

Publications and source records attributed to Aidan Crilly.

7 recordsLinked to original sources

arXiv2026

NeSST: A Python Tool for Neutron Spectra and Synthetic Diagnostics in Inertial Confinement Fusion

We present the Neutron Scattered Spectra Tool (NeSST), an open-source Python package for rapidly constructing primary and singly scattered neutron spectra from inertial confinement fusion (ICF) implosions. NeSST evaluates primary spectra for deuterium-tritium (DT), deuterium-deuterium (DD) and tritium-tritium (TT) reactions. Differential and total nuclear cross sections are read directly from Evaluated Nuclear Data File (ENDF) libraries. This enables elastic ($n$D, $n$T) and inelastic [D$(n,2n)$p, T$(n,2n)$D] scattering from DT fuel, as well as scattering from additional ablator materials such as $^{12}$C, to be treated within a common framework. Relativistic corrections to elastic scattering kinematics are included. Areal density asymmetries are incorporated through a Legendre mode expansion of the neutron-averaged projected areal density, allowing the spectral signatures of implosion non-uniformities to be computed and fitted. The effect of scattering ion velocities on the neutron backscatter edge shape is handled through pre-computed ion-velocity-dependent scattering kernels. A synthetic neutron time-of-flight (nToF) module converts energy spectra into detector signals with a full forward model that includes configurable instrument response functions (IRFs), energy-dependent scintillator sensitivity, and beamline attenuation. The code is publicly available at https://github.com/aidancrilly/NeSST

physics.plasm-ph↗

arXiv2022

Constraints on Ion Velocity Distributions from Fusion Product Spectroscopy

Recent inertial confinement fusion experiments have shown primary fusion spectral moments which are incompatible with a Maxwellian velocity distribution description. These results show that an ion kinetic description of the reacting ions is necessary. We develop a theoretical classification of non-Maxwellian ion velocity distributions using the spectral moments. At the mesoscopic level, a monoenergetic decomposition of the velocity distribution reveals there are constraints on the space of spectral moments accessible by isotropic distributions. General expressions for the directionally dependent spectral moments of anisotropic distributions are derived. At the macroscopic level, a distribution of fluid element velocities modifies the spectral moments in a constrained manner. Experimental observations can be compared to these constraints to identify the character and isotropy of the underlying reactant ion velocity distribution and determine if the plasma is hydrodynamic or kinetic.

physics.plasm-ph↗

arXiv2022

Investigating radiatively driven, magnetised plasmas with a university scale pulsed-power generator

We present first results from a novel experimental platform which is able to access physics relevant to topics including indirect-drive magnetised ICF; laser energy deposition; various topics in atomic physics; and laboratory astrophysics (for example the penetration of B-fields into HED plasmas). This platform uses the X-Rays from a wire array Z-Pinch to irradiate a silicon target, producing an outflow of ablated plasma. The ablated plasma expands into ambient, dynamically significant B-fields (~5 T) which are supported by the current flowing through the Z-Pinch. The outflows have a well-defined (quasi-1D) morphology, enabling the study of fundamental processes typically only available in more complex, integrated schemes. Experiments were fielded on the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine a wire array Z-Pinch produces an X-Ray pulse carrying a total energy of ~15 kJ over ~30 ns. This equates to an average brightness temperature of around 10 eV on-target.

physics.plasm-ph↗

arXiv2021

Exploring extreme magnetization phenomena in directly-driven imploding cylindrical targets

This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realisable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10~kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally-driven or current-driven transport is dominating.

physics.plasm-ph↗

arXiv2020

The Effect of Areal Density Asymmetries on Scattered Neutron Spectra in ICF Implosions

Scattered neutron spectroscopy is a diagnostic technique commonly used to measure areal density in ICF experiments. Deleterious areal density asymmetries modify the shape of the scattered neutron spectrum. In this work a novel analysis is developed which can be used to fit the shape change. This allows scattered neutron spectroscopy to directly infer the amplitude and mode of the areal density asymmetries, with little sensitivity to confounding factors which affect other diagnostics for areal density. The model is tested on spectra produced by a neutron transport calculation with both isotropic and anisotropic primary fusion neutron sources. Multiple lines of sight are required to infer the areal density distribution over the whole sphere -- we investigate the error propagation and optimal detector arrangement associated with this inference.

physics.plasm-ph↗

arXiv2019

Synthetic Nuclear Diagnostics for Inferring Plasma Properties of Inertial Confinement Fusion Implosions

A suite of synthetic nuclear diagnostics has been developed to post-process radiation hydrodynamics simulations performed with the code Chimera. These provide experimental observables based on simulated capsule properties and are used to assess alternative experimental and data analysis techniques. These diagnostics include neutron spectroscopy, primary and scattered neutron imaging, neutron activation, $γ$-ray time histories and carbon $γ$-ray imaging. Novel features of the neutron spectrum have been analysed to infer plasma parameters. The nT and nD backscatter edges have been shown to provide a shell velocity measurement. Areal density asymmetries created by low mode perturbations have been inferred from the slope of the downscatter spectrum down to 10 MeV. Neutron activation diagnostics showed significant aliasing of high mode areal density asymmetries when observing a capsule implosion with 3D multimode perturbations applied. Carbon $γ$-ray imaging could be used to image the ablator at high convergence ratio. Time histories of both the fusion and carbon $γ$ signals showed a greater time difference between peak intensities for the perturbed case when compared to a symmetric simulation.

physics.plasm-ph↗

arXiv2016

Evidence that the maximum electron energy in hotspots of FR II galaxies is not determined by synchrotron cooling

It has been suggested that relativistic shocks in extragalactic sources may accelerate the highest energy cosmic rays. The maximum energy to which cosmic rays can be accelerated depends on the structure of magnetic turbulence near the shock but recent theoretical advances indicate that relativistic shocks are probably unable to accelerate particles to energies much larger than a PeV. We study the hotspots of powerful radiogalaxies, where electrons accelerated at the termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is < TeV for a canonical magnetic field of ~100 micro Gauss. Based on theoretical considerations we show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test this result by considering a sample of hotspots observed with high spatial resolution at radio, infrared and optical wavelengths.

astro-ph.HE↗