N. J. Hartley

N. J. Hartley

Research Associate

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A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.

Pages

Posts

Future Blog Post

less than 1 minute read

Published:

This post will show up by default. To disable scheduling of future posts, edit config.yml and set future: false.

Blog Post number 4

less than 1 minute read

Published:

This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.

Blog Post number 3

less than 1 minute read

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This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.

Blog Post number 2

less than 1 minute read

Published:

This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.

Blog Post number 1

less than 1 minute read

Published:

This is a sample blog post. Lorem ipsum I can’t remember the rest of lorem ipsum and don’t have an internet connection right now. Testing testing testing this blog post. Blog posts are cool.

portfolio

publications

Evidence for Crystalline Structure in Dynamically-Compressed Polyethylene up to 200 GPa

Published in Scientific Reports, 2019

We investigated the high-pressure behavior of polyethylene (CH2) by probing dynamically-compressed samples with X-ray diffraction. At pressures up to 200 GPa, comparable to those present inside icy giant planets (Uranus, Neptune), shock-compressed polyethylene retains a polymer crystal structure, from which we infer the presence of significant covalent bonding.

Recommended citation: N. J. Hartley et al. Sci. Rep. 9 (2019) 4196. https://www.nature.com/articles/s41598-019-40782-5

Ultrafast anisotropic disordering in graphite driven by intense hard X-ray pulses

Published in High Energy Density Physics, 2019

We observed the behaviour of graphite after heating by an X-ray free electron laser (XFEL) beam at an intensity on the order of 10^19 W/cm2. The interplanar diffraction peaks weaken significantly within 10s of femtoseconds, but in-plane diffraction orders i.e. those with Miller Index (hk0), persist up to 300 fs, with the observed signal increasing. We interpret this as nonthermal damage through the breaking of interplanar bonds, which at longer timescales leads to ablation by removal of intact graphite sheets, rather than by melting.

Recommended citation: N. J. Hartley et al. HEDP 32 (2019) 63-69. https://www.sciencedirect.com/science/article/pii/S1574181819300321

Dynamically pre-compressed hydrocarbons studied by self-impedance mismatch

Published in Matter and Radiation at Extremes, 2020

Using the SG-III prototype laser at China Academy of Engineering Physics, Mianyang, we irradiated polystyrene (CH) samples with a thermal radiation drive, reaching conditions on the principal Hugoniot up to P ≈ 1 TPa (10 Mbar), and away from the Hugoniot up to P ≈ 300 GPa (3 Mbar). The response of each sample was measured with a velocity interferometry diagnostic to determine the material and shock velocity, and hence the conditions reached, and the reflectivity of the sample, from which changes in the conductivity can be inferred. By applying the selfimpedance mismatch technique with the measured velocities, the pressure and density of thermodynamic points away from the principal Hugoniot were determined. Our results show an unexpectedly large reflectivity at the highest shock pressures, while the off-Hugoniot points agree with previous work suggesting that shock-compressed CH conductivity is primarily temperature-dependent.

Recommended citation: N. J. Hartley et al. MRE 5.2 (2020) 028401. https://pubs.aip.org/mre/article/5/2/028401/253010/Dynamically-pre-compressed-hydrocarbons-studied-by

Using Diffuse Scattering to Observe X-Ray-Driven Nonthermal Melting

Published in Physical Review Letters, 2021

Using a high intensity (∼ 10^20 W/cm2) X-ray pump X-ray probe scheme, we observed changes in the ionic structure of silicon induced by X-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in incoherent scattering, which we attribute to a loss of lattice order and a transition to a liquid state within 100 fs of irradiation, a timescale which agrees well with first principles simulations. This method is capable of observing liquid scattering without masking or filtering of signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change.

Recommended citation: N. J. Hartley et al. PRL 126.1 (2021) 015703. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.015703

Confirming X-ray parametric down conversion by time–energy correlation

Published in Results in Physics, 2024

We present measurements of X-ray Parametric Down Conversion at the Advanced Photon Source synchrotron facility. Using an incoming pump beam at 22 keV, we observe the simultaneous, elastic emission of down-converted photon pairs generated in a diamond crystal. The pairs are detected using high count rate silicon drift detectors with low noise. Production by down-conversion is confirmed by measuring time-energy correlations in the detector signal, where photon pairs within an energy window ranging from 10 to 12 keV are only observed at short time differences. By systematically varying the crystal misalignment and detector positions, we obtain results that are consistent with the constant total of the down-converted signal. Our maximum rate of observed pairs was 130 /hour, corresponding to a conversion efficiency for the down-conversion process of 5.3 ± 0.5 × 10^−13

Recommended citation: N. J. Hartley et al. Res. Phys. 57 (2021) 107328. https://www.sciencedirect.com/science/article/pii/S221137972400010X

talks

Hydrocarbons at Extreme Conditions

Published:

Presenting results on shock compression results to the High Pressure Plasma and Planetary Physics (HP4) Workshop.

teaching

Teaching experience 1

Undergraduate course, University 1, Department, 2014

This is a description of a teaching experience. You can use markdown like any other post.

Teaching experience 2

Workshop, University 1, Department, 2015

This is a description of a teaching experience. You can use markdown like any other post.