Publications


Phase transition lowering in dynamically compressed silicon

NATURE PHYSICS 15 (2019) 89-+

EE McBride, A Krygier, A Ehnes, E Galtier, M Harmand, Z Konopkova, HJ Lee, H-P Liermann, B Nagler, A Pelka, M Roedel, A Schropp, RF Smith, C Spindloe, D Swift, F Tavella, S Toleikis, T Tschentscher, JS Wark, A Higginbotham


First demonstration of ARC-accelerated proton beams at the National Ignition Facility

Physics of Plasmas 26 (2019)

D Mariscal, T Ma, SC Wilks, AJ Kemp, GJ Williams, P Michel, H Chen, PK Patel, BA Remington, M Bowers, L Pelz, MR Hermann, W Hsing, D Martinez, R Sigurdsson, M Prantil, A Conder, J Lawson, M Hamamoto, P Di Nicola, C Widmayer, D Homoelle, R Lowe-Webb, S Herriot, W Williams, D Alessi, D Kalantar, R Zacharias, C Haefner, N Thompson, T Zobrist, D Lord, N Hash, A Pak, N Lemos, M Tabak, C McGuffey, J Kim, FN Beg, MS Wei, P Norreys, A Morace, N Iwata, Y Sentoku, D Neely, GG Scott, K Flippo

© 2019 Author(s). New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic (∼10 18 W/cm 2 ) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large ∼100 μm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux ∼ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.


Radiation transfer in cylindrical, toroidal and hemi-ellipsoidal plasmas

Journal of Quantitative Spectroscopy and Radiative Transfer Elsevier BV (2019)

G Pérez-Callejo, JS Wark, SJ Rose


Recovery of metastable dense Bi synthesized by shock compression

APPLIED PHYSICS LETTERS 114 (2019) ARTN 120601

MG Gorman, AL Coleman, R Briggs, RS McWilliams, A Hermann, D McGonegle, CA Bolme, AE Gleason, E Galtier, HJ Lee, E Granados, EE McBride, S Rothman, DE Fratanduono, RF Smith, GW Collins, JH Eggert, JS Wark, MI McMahon


The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

HIGH ENERGY DENSITY PHYSICS 30 (2019) 45-51

G Perez-Callejo, DA Liedahl, MB Schneider, SJ Rose, JS Wark


Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum.

Physical review letters 120 (2018) 265502-

M Sliwa, D McGonegle, C Wehrenberg, CA Bolme, PG Heighway, A Higginbotham, A Lazicki, HJ Lee, B Nagler, HS Park, RE Rudd, MJ Suggit, D Swift, F Tavella, L Zepeda-Ruiz, BA Remington, JS Wark

We have used femtosecond x-ray diffraction to study laser-shocked fiber-textured polycrystalline tantalum targets as the 37-253 GPa shock waves break out from the free surface. We extract the time and depth-dependent strain profiles within the Ta target as the rarefaction wave travels back into the bulk of the sample. In agreement with molecular dynamics simulations, the lattice rotation and the twins that are formed under shock compression are observed to be almost fully eliminated by the rarefaction process.


Comments on A new theory for X-ray diffraction.

Acta crystallographica. Section A, Foundations and advances 74 (2018) 447-456

JT Fraser, JS Wark

In an article entitled A new theory for X-ray diffraction [Fewster (2014). Acta Cryst. A70, 257-282], hereafter referred to as NTXRD, it is claimed that when X-rays are scattered from a small crystallite, whatever its size and shape, the diffraction pattern will contain enhanced scattering at angles of exactly 2θB, whatever the orientation of the crystal. It is claimed that in this way scattering from a powder, with randomly oriented crystals, gives rise to Bragg scattering even if the Bragg condition is never satisfied by an individual crystallite. The claims of the theory put forward in NTXRD are examined and they are found to be in error. Whilst for a certain restricted set of shapes of crystals it is possible to obtain some diffraction close to (but not exactly at) the Bragg angle as the crystallite is oriented away from the Bragg condition, this is generally not the case. Furthermore, contrary to the claims made within NTXRD, the recognition of the origin of the type of effects described is not new, and has been known since the earliest days of X-ray diffraction.


Simultaneous 8.2 keV phase-contrast imaging and 24.6 keV X-ray diffraction from shock-compressed matter at the LCLS

APPLIED PHYSICS LETTERS 112 (2018) ARTN 221907

F Seiboth, LB Fletcher, D McGonegle, S Anzellini, LE Dresselhaus-Cooper, M Frost, E Galtier, S Goede, M Harmand, HJ Lee, AL Levitan, K Miyanishi, B Nagler, I Nam, N Ozaki, M Roedel, A Schropp, C Spindloe, P Sun, JS Wark, J Hastings, SH Glenzer, EE McBride


Observation of Laser Power Amplification in a Self-Injecting Laser Wakefield Accelerator

Physical Review Letters 120 (2018)

MJV Streeter, S Kneip, MS Bloom, RA Bendoyro, O Chekhlov, AE Dangor, A Döpp, CJ Hooker, J Holloway, J Jiang, NC Lopes, H Nakamura, PA Norreys, CAJ Palmer, PP Rajeev, J Schreiber, DR Symes, M Wing, SPD Mangles, Z Najmudin

© 2018 American Physical Society. We report on the depletion and power amplification of the driving laser pulse in a strongly driven laser wakefield accelerator. Simultaneous measurement of the transmitted pulse energy and temporal shape indicate an increase in peak power from 187±11 TW to a maximum of 318±12 TW after 13 mm of propagation in a plasma density of 0.9×1018 cm-3. The power amplification is correlated with the injection and acceleration of electrons in the nonlinear wakefield. This process is modeled by including a localized redshift and subsequent group delay dispersion at the laser pulse front.


Single-shot frequency-resolved optical gating for retrieving the pulse shape of high energy picosecond pulses.

The Review of scientific instruments 89 (2018) 103509-

R Aboushelbaya, AF Savin, L Ceurvorst, J Sadler, PA Norreys, AS Davies, DH Froula, A Boyle, M Galimberti, P Oliveira, B Parry, Y Katzir, K Glize

Accurate characterization of laser pulses used in experiments is a crucial step to the analysis of their results. In this paper, a novel single-shot frequency-resolved optical gating (FROG) device is described, one that incorporates a dispersive element which allows it to fully characterize pulses up to 25 ps in duration with a 65 fs per pixel temporal resolution. A newly developed phase retrieval routine based on memetic algorithms is implemented and shown to circumvent the stagnation problem that often occurs with traditional FROG analysis programs when they encounter a local minimum.


Femtosecond diffraction studies of solid and liquid phase changes in shock-compressed bismuth.

Scientific reports 8 (2018) 16927-16927

MG Gorman, AL Coleman, R Briggs, RS McWilliams, D McGonegle, CA Bolme, AE Gleason, E Galtier, HJ Lee, E Granados, M Śliwa, C Sanloup, S Rothman, DE Fratanduono, RF Smith, GW Collins, JH Eggert, JS Wark, MI McMahon

Bismuth has long been a prototypical system for investigating phase transformations and melting at high pressure. Despite decades of experimental study, however, the lattice-level response of Bi to rapid (shock) compression and the relationship between structures occurring dynamically and those observed during slow (static) compression, are still not clearly understood. We have determined the structural response of shock-compressed Bi to 68 GPa using femtosecond X-ray diffraction, thereby revealing the phase transition sequence and equation-of-state in unprecedented detail for the first time. We show that shocked-Bi exhibits a marked departure from equilibrium behavior - the incommensurate Bi-III phase is not observed, but rather a new metastable phase, and the Bi-V phase is formed at significantly lower pressures compared to static compression studies. We also directly measure structural changes in a shocked liquid for the first time. These observations reveal new behaviour in the solid and liquid phases of a shocked material and give important insights into the validity of comparing static and dynamic datasets.


ALICE: A non-LTE plasma atomic physics, kinetics and lineshape package

HIGH ENERGY DENSITY PHYSICS 26 (2018) 56-67

EG Hill, G Perez-Callejo, SJ Rose


Developing an Experimental Basis for Understanding Transport in NIF Hohlraum Plasmas.

Physical review letters 121 (2018) 095002-095002

MA Barrios, JD Moody, LJ Suter, M Sherlock, H Chen, W Farmer, J Jaquez, O Jones, RL Kauffman, JD Kilkenny, J Kroll, OL Landen, DA Liedahl, SA Maclaren, NB Meezan, A Nikroo, MB Schneider, DB Thorn, K Widmann, G Pérez-Callejo

We report on the first multilocation electron temperature (T_{e}) and flow measurements in an ignition hohlraum at the National Ignition Facility using the novel technique of mid-Z spectroscopic tracer "dots." The measurements define a low resolution "map" of hohlraum plasma conditions and provide a basis for the first multilocation tests of particle and energy transport physics in a laser-driven x-ray cavity. The data set is consistent with classical heat flow near the capsule but reduced heat flow near the laser entrance hole. We evaluate the role of kinetic effects, self-generated magnetic fields, and instabilities in causing spatially dependent heat transport in the hohlraum.


Channel optimization of high-intensity laser beams in millimeter-scale plasmas.

Physical review. E 97 (2018) 043208-

L Ceurvorst, A Savin, N Ratan, MF Kasim, J Sadler, PA Norreys, H Habara, KA Tanaka, S Zhang, MS Wei, S Ivancic, DH Froula, W Theobald

Channeling experiments were performed at the OMEGA EP facility using relativistic intensity (>10^{18}W/cm^{2}) kilojoule laser pulses through large density scale length (∼390-570 μm) laser-produced plasmas, demonstrating the effects of the pulse's focal location and intensity as well as the plasma's temperature on the resulting channel formation. The results show deeper channeling when focused into hot plasmas and at lower densities, as expected. However, contrary to previous large-scale particle-in-cell studies, the results also indicate deeper penetration by short (10 ps), intense pulses compared to their longer-duration equivalents. This new observation has many implications for future laser-plasma research in the relativistic regime.


Advantages to a diverging Raman amplifier

Communications Physics Springer Science and Business Media LLC 1 (2018) 19

JD Sadler, LO Silva, RA Fonseca, K Glize, MF Kasim, A Savin, R Aboushelbaya, MW Mayr, B Spiers, RHW Wang, R Bingham, RMGM Trines, PA Norreys


Soft X-ray backlighter source driven by a short-pulse laser for pump-probe characterization of warm dense matter.

The Review of scientific instruments 89 (2018) 10F122-

C McGuffey, M Dozières, J Kim, A Savin, J Park, J Emig, C Brabetz, L Carlson, RF Heeter, HS McLean, J Moody, MB Schneider, MS Wei, FN Beg

Here we propose a pump-probe X-ray absorption spectroscopy temperature measurement technique appropriate for matter having temperature in the range of 10 to a few 100 eV and density up to solid density. Atomic modeling simulations indicate that for various low- to mid-Z materials in this range the energy and optical depth of bound-bound and bound-free absorption features are sensitive to temperature. We discuss sample thickness and tamp layer considerations. A series of experimental investigations was carried out using a range of laser parameters with pulse duration ≤5 ps and various pure and alloyed materials to identify backlighter sources suitable for the technique.


Validating Continuum Lowering Models via Multi-Wavelength Measurements of Integrated X-ray Emission.

Scientific reports 8 (2018) 6276-

MF Kasim, JS Wark, SM Vinko

X-ray emission spectroscopy is a well-established technique used to study continuum lowering in dense plasmas. It relies on accurate atomic physics models to robustly reproduce high-resolution emission spectra, and depends on our ability to identify spectroscopic signatures such as emission lines or ionization edges of individual charge states within the plasma. Here we describe a method that forgoes these requirements, enabling the validation of different continuum lowering models based solely on the total intensity of plasma emission in systems driven by narrow-bandwidth x-ray pulses across a range of wavelengths. The method is tested on published Al spectroscopy data and applied to the new case of solid-density partially-ionized Fe plasmas, where extracting ionization edges directly is precluded by the significant overlap of emission from a wide range of charge states.


Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy.

Physical review letters 120 (2018) 055002-

QY van den Berg, EV Fernandez-Tello, T Burian, J Chalupský, H-K Chung, O Ciricosta, GL Dakovski, V Hájková, P Hollebon, L Juha, J Krzywinski, RW Lee, MP Minitti, TR Preston, AG de la Varga, V Vozda, U Zastrau, JS Wark, P Velarde, SM Vinko

Electron-ion collisional dynamics is of fundamental importance in determining plasma transport properties, nonequilibrium plasma evolution, and electron damage in diffraction imaging applications using bright x-ray free-electron lasers (FELs). Here we describe the first experimental measurements of ultrafast electron impact collisional ionization dynamics using resonant core-hole spectroscopy in a solid-density magnesium plasma, created and diagnosed with the Linac Coherent Light Source x-ray FEL. By resonantly pumping the 1s→2p transition in highly charged ions within an optically thin plasma, we have measured how off-resonance charge states are populated via collisional processes on femtosecond time scales. We present a collisional cross section model that matches our results and demonstrates how the cross sections are enhanced by dense-plasma effects including continuum lowering. Nonlocal thermodynamic equilibrium collisional radiative simulations show excellent agreement with the experimental results and provide new insight on collisional ionization and three-body-recombination processes in the dense-plasma regime.


In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics.

Nature 550 (2017) 496-499

CE Wehrenberg, D McGonegle, C Bolme, A Higginbotham, A Lazicki, HJ Lee, B Nagler, H-S Park, BA Remington, RE Rudd, M Sliwa, M Suggit, D Swift, F Tavella, L Zepeda-Ruiz, JS Wark

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum-an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.


Brilliant X-rays using a Two-Stage Plasma Insertion Device.

Scientific reports 7 (2017) 3985-

JA Holloway, PA Norreys, AGR Thomas, R Bartolini, R Bingham, J Nydell, RMGM Trines, R Walker, M Wing

Particle accelerators have made an enormous impact in all fields of natural sciences, from elementary particle physics, to the imaging of proteins and the development of new pharmaceuticals. Modern light sources have advanced many fields by providing extraordinarily bright, short X-ray pulses. Here we present a novel numerical study, demonstrating that existing third generation light sources can significantly enhance the brightness and photon energy of their X-ray pulses by undulating their beams within plasma wakefields. This study shows that a three order of magnitude increase in X-ray brightness and over an order of magnitude increase in X-ray photon energy is achieved by passing a 3 GeV electron beam through a two-stage plasma insertion device. The production mechanism micro-bunches the electron beam and ensures the pulses are radially polarised on creation. We also demonstrate that the micro-bunched electron beam is itself an effective wakefield driver that can potentially accelerate a witness electron beam up to 6 GeV.

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