Dense plasma heating by crossing relativistic electron beams

Physical Review E American Physical Society 95 (2016) 013211

N Ratan, NJ Sircombe, LA Ceurvorst, J Sadler, MF Kasim, J Holloway, MC Levy, R Trines, R Bingham, P Norreys

Here we investigate, using relativistic fluid theory and Vlasov-Maxwell simulations, the local heating of a dense plasma by two crossing electron beams. Heating occurs as an instability of the electron beams drives Langmuir waves which couple nonlinearly into damped ion-acoustic waves. Simulations show a factor 2.8 increase in electron kinetic energy with a coupling efficiency of 18%. Our results support applications to the production of warm dense matter and as a driver for inertial fusion plasmas.

Path to AWAKE: Evolution of the concept


A Caldwell, E Adli, L Amorim, R Apsimon, T Argyropoulos, R Assmann, A-M Bachmann, E Batsch, J Bauche, VKB Olsen, M Bernardini, R Bingham, B Biskup, T Bohl, C Bracco, PN Burrows, G Burt, B Buttenschoen, A Butterworth, M Cascella, S Chattopadhyay, E Chevallay, S Cipiccia, H Damerau, L Deacon, R Dirksen, S Doebert, U Dorda, E Eisen, J Farmer, S Fartoukh, V Fedosseev, E Feldbaumer, R Fiorito, R Fonseca, F Friebel, G Geschonke, B Goddard, AA Gorn, O Grulke, E Gschwendtner, J Hansen, C Hessler, S Hillenbrand, W Hofle, J Holloway, C Huang, M Huether, D Jaroszynski, L Jensen, S Jolly, A Joulaei, M Kasim, F Keeble, R Kersevan, N Kumar, Y Li, S Liu, N Lopes, KV Lotov, W Lu, J Machacek, S Mandry, I Martin, R Martorelli, M Martyanov, S Mazzoni, M Meddahi, L Merminga, O Mete, VA Minakov, J Mitchell, J Moody, A-S Mueller, Z Najmudin, TCQ Noakes, P Norreys, J Osterhoff, E Oez, A Pardons, K Pepitone, A Petrenko, G Plyushchev, J Pozimski, A Pukhov, O Reimann, K Rieger, S Roesler, H Ruhl, T Rusnak, E Salveter, N Savard, J Schmidt, H von der Schmitt, A Seryi, E Shaposhnikova, ZM Sheng, R Sherwood, L Silva, F Simon, L Soby, AP Sosedkin, RI Spitsyn, T Tajima, R Tarkeshian, H Timko, R Trines, T Tueckmantel, PV Tuev, M Turner, E Velotti, V Verzilov, J Vieira, H Vincke, Y Wei, CP Welsch, M Wing, G Xia, V Yakimenko, H Zhang, F Zimmermann

Transport coefficients of a relativistic plasma

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics American Physical Society 93 (2016) 1-16

SJ Rose, OJ Pike

In this work, a self-consistent transport theory for a relativistic plasma is developed. Using the notation of Braginskii [S. I. Braginskii, in Reviews of Plasma Physics, ed. M. A. Leontovich (1965), Vol. 1, p.174], we provide semi-analytical forms of the electrical resistivity, thermoelectric and thermal conductivity tensors for a Lorentzian plasma in a magnetic field. This treatment is then generalized to plasmas with arbitrary atomic number by numerically solving the linearized Boltzmann equation. The corresponding transport coefficients are fitted by rational functions in order to make them suitable for use in radiation-hydrodynamic simulations and transport calculations. Within the confines of linear transport theory and on the assumption that the plasma is optically thin, our results are valid for temperatures up to a few MeV. By contrast, classical transport theory begins to incur significant errors above kBT ~ 10 keV, e.g., the parallel thermal conductivity is suppressed by 15% at kBT = 20 keV due to relativistic effects

Laboratory astrophysical collisionless shock experiments on Omega and NIF

Journal of Physics: Conference Series IOP Publishing Ltd. 688 (2016) 012084-012084

HS Park, JS Ross, CM Huntington, F Fiuza, D Ryutov, D Casey, RP Drake, G Fiksel, D Froula, G Gregori, NL Kugland, C Kuranz, MC Levy, CK Li, J Meinecke, T Morita, R Petrasso, C Plechaty, B Remington, Y Sakawa, A Spitkovsky, H Takabe

We are performing scaled astrophysics experiments on Omega and on NIF. Laser driven counter-streaming interpenetrating supersonic plasma flows can be studied to understand astrophysical electromagnetic plasma phenomena in a controlled laboratory setting. In our Omega experiments, the counter-streaming flow plasma state is measured using Thomson scattering diagnostics, demonstrating the plasma flows are indeed super-sonic and in the collisionless regime. We observe a surprising additional electron and ion heating from ion drag force in the double flow experiments that are attributed to the ion drag force and electrostatic instabilities. [1] A proton probe is used to image the electric and magnetic fields. We observe unexpected large, stable and reproducible electromagnetic field structures that arise in the counter-streaming flows [2]. The Biermann battery magnetic field generated near the target plane, advected along the flows, and recompressed near the midplane explains the cause of such self-organizing field structures [3]. A D3He implosion proton probe image showed very clear filamentary structures; three-dimensional Particle-In-Cell simulations and simulated proton radiography images indicate that these filamentary structures are generated by Weibel instabilities and that the magnetization level (ratio of magnetic energy over kinetic energy in the system) is ∼0.01 [4]. These findings have very high astrophysical relevance and significant implications. We expect to observe true collisionless shock formation when we use >100 kJ laser energy on NIF.

Relativistic intensity laser interactions with low-density plasmas

Journal of Physics: Conference Series IOP Publishing 688 (2016) 012126-012126

L Willingale, PM Nilson, C Zulick, H Chen, RS Craxton, J Cobble, A Maksimchuk, P Norreys, TC Sangster, RHH Scott, C Stoeckl

© Published under licence by IOP Publishing Ltd. We perform relativistic-intensity laser experiments using the Omega EP laser to investigate channeling phenomena and particle acceleration in underdense plasmas. A fundamental understanding of these processes is of importance to the hole-boring fast ignition scheme for inertial confinement fusion. Proton probing was used to image the electromagnetic fields formed as the Omega EP laser pulse generated a channel through underdense plasma. Filamentation of the channel was observed, followed by self-correction into a single channel. The channel radius as a function of time was found to be in reasonable agreement with momentum- conserving snowplough models.

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering

Nature Communications Nature Publishing 7 (2016) 10371

J Vieira, RMGM Trines, EP Alves, RA Fonseca, JT Mendonça, R Bingham, P Norreys, LO Silva

Twisted Laguerre–Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser–matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high–energy-density science, compact plasma-based accelerators and light sources.

Nanosecond formation of diamond and lonsdaleite by shock compression of graphite

Nature Communications Nature Publishing Group 7 (2016) 10970

D Kraus, A Ravasio, M Gauthier, DO Gericke, J Vorberger, S Frydrych, J Helfrich, LB Fletcher, G Schaumann, B Nagler, B Barbrel, B Bachmann, EJ Gamboa, S Göde, E Granados, G Gregori, HJ Lee, P Neumayer, W Schumaker, T Döppner, RW Falcone, SH Glenzer, M Roth

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.

Theory of density fluctuations in strongly radiative plasmas

Physical Review E American Physical Society 93 (2016) 033201

JE Cross, P Mabey, DO Gericke, G Gregori

Derivation of the dynamic structure factor, an important parameter linking experimental and theoretical work in dense plasmas, is possible starting from hydrodynamic equations. Here we obtain, by modifying the governing hydrodynamic equations, a new form of the dynamic structure factor which includes radiative terms. The inclusion of such terms has an effect on the structure factor at high temperatures, which suggests that its effect must be taken into consideration in such regimes.

Model experiment of magnetic field amplification in laser-produced plasmas via the Richtmyer-Meshkov instability

Physics of Plasmas AIP Publishing 23 (2016) 032126-032126

Y Kuramitsu, N Ohnishi, Y Sakawa, T Morita, H Tanji, T Ide, K Nishio, CD Gregory, JN Waugh, N Booth, R Heathcote, C Murphy, G Gregori, J Smallcombe, C Barton, A Dizière, M Koenig, N Woolsey, Y Matsumoto, A Mizuta, T Sugiyama, S Matsukiyo, T Moritaka, T Sano, H Takabe

A model experiment of magnetic field amplification (MFA) via the Richtmyer-Meshkov instability (RMI) in supernova remnants (SNRs) was performed using a high-power laser. In order to account for very-fast acceleration of cosmic rays observed in SNRs, it is considered that the magnetic field has to be amplified by orders of magnitude from its background level. A possible mechanism for the MFA in SNRs is stretching and mixing of the magnetic field via the RMI when shock waves pass through dense molecular clouds in interstellar media. In order to model the astrophysical phenomenon in laboratories, there are three necessary factors for the RMI to be operative: a shock wave, an external magnetic field, and density inhomogeneity. By irradiating a double-foil target with several laser beams with focal spot displacement under influence of an external magnetic field, shock waves were excited and passed through the density inhomogeneity. Radiative hydrodynamic simulations show that the RMI evolves as the density inhomogeneity is shocked, resulting in higher MFA.

Detailed model for hot-dense aluminum plasmas generated by an X-ray free electron laser

Physics of Plasmas American Institute of Physics 23 (2016)

O Ciricosta, SM Vinko, HK Chung, C Jackson, RW Lee, TR Preston, DS Rackstraw, JS Wark

The possibility of creating hot-dense plasma samples by isochoric heating of solid targets with high-intensity femtosecond X-ray lasers has opened up new opportunities in the experimental study of such systems. A study of the X-ray spectra emitted from solid density plasmas has provided significant insight into the X-ray absorption mechanisms, subsequent target heating, and the conditions of temperature, electron density, and ionization stages produced (Vinko et al., Nature 482, 59–62 (2012)). Furthermore, detailed analysis of the spectra has provided new information on the degree of ionization potential depression in these strongly coupled plasmas (Ciricosta et al., Phys. Rev. Lett. 109, 065002 (2012)). Excellent agreement between experimental and simulated spectra has been obtained, but a full outline of the procedure by which this has been achieved has yet to be documented. We present here the details and approximations concerning the modelling of the experiment described in the above referenced work. We show that it is crucial to take into account the spatial and temporal gradients in simulating the overall emission spectra, and discuss how aspects of the model used affect the interpretation of the data in terms of charge-resolved measurements of the ionization potential depression.

Simulations of the time and space-resolved X-ray transmission of a free-electron-laser-heated aluminium plasma

Journal of Physics B: Atomic, Molecular and Optical Physics IOP Publishing 49 (2016) 035603

DS Rackstraw, SM Vinko, O Ciricosta, H-K Chung, RW Lee, JS Wark

<p>We present simulations of the time and space-resolved transmission of a solid-density aluminium plasma as it is created and probed with the focussed output of an x-ray free-electron-laser with photon energies ranging from the K-edge of the cold material (1560 eV) to 1880 eV. We demonstrate how information about the temporal evolution of the charge states within the system can be extracted from the spatially resolved, yet time-integrated transmission images. We propose that such time-resolved measurements could in principle be performed with recently developed split-and-delay techniques.</p>

Efficient evaluation of collisional energy transfer terms for plasma particle simulations


AE Turrell, M Sherlock, SJ Rose



S Kerr, MZ Mo, R Masud, X Jin, L Manzoor, HF Tiedje, Y Tsui, R Fedosejevs, A Link, P Patel, HS McLean, A Hazi, H Chen, L Ceurvorst, P Norreys, IEEE

Compression of X-ray free electron laser pulses to attosecond duration

Scientific Reports Nature Publishing Group 5 (2015) 16755-16755

JD Sadler, R Nathvani, P Oleśkiewicz, LA Ceurvorst, N Ratan, MF Kasim, RMGM Trines, R Bingham, P Norreys

State of the art X-ray Free Electron Laser facilities currently provide the brightest X-ray pulses available, typically with mJ energy and several hundred femtosecond duration. Here we present one- and two-dimensional Particle-in-Cell simulations, utilising the process of stimulated Raman amplification, showing that these pulses are compressed to a temporally coherent, sub-femtosecond pulse at 8% efficiency. Pulses of this type may pave the way for routine time resolution of electrons in nm size potentials. Furthermore, evidence is presented that significant Landau damping and wave-breaking may be beneficial in distorting the rear of the interaction and further reducing the final pulse duration.

Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs.

Nature communications 6 (2015) 8742-

N Booth, APL Robinson, P Hakel, RJ Clarke, RJ Dance, D Doria, LA Gizzi, G Gregori, P Koester, L Labate, T Levato, B Li, M Makita, RC Mancini, J Pasley, PP Rajeev, D Riley, E Wagenaars, JN Waugh, NC Woolsey

Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.

Ultra-fast collisional ion heating by electrostatic shocks

Nature Communications Nature Publishing Group 6 (2015) 8905

A Turrell, M Sherlock, SJ Rose

High intensity lasers can be used to generate shockwaves which have found applications in nuclear fusion, proton imaging, cancer therapies, and materials science. Collisionless electrostatic shocks are one type of shockwave widely studied for applications involving ion acceleration. Here we show a novel mechanism for collisionless electrostatic shocks to heat small amounts of solid density matter to temperatures of ∼ keV in tens of femtoseconds. Unusually, electrons play no direct role in the heating, and it is the ions which determine the heating rate. Ions are heated due to an interplay between the electric field of the shock, the local density increase during the passage of the shock, and collisions between different species of ion. In simulations, these factors combine to produce rapid, localised heating of the lighter ion species. Although the heated volume is modest, this would be one of the fastest heating mechanisms discovered if demonstrated in the laboratory.

Mitigating the relativistic laser beam filamentation via an elliptical beam profile.

Physical review. E, Statistical, nonlinear, and soft matter physics American Physical Society 92 (2015) 053106-

TW Huang, CT Zhou, AP Robinson, B Qiao, H Zhang, SZ Wu, HB Zhuo, P Norreys, XT He

It is shown that the filamentation instability of relativistically intense laser pulses in plasmas can be mitigated in the case where the laser beam has an elliptically distributed beam profile. A high-power elliptical Gaussian laser beam would break up into a regular filamentation pattern-in contrast to the randomly distributed filaments of a circularly distributed laser beam-and much more laser power would be concentrated in the central region. A highly elliptically distributed laser beam experiences anisotropic self-focusing and diffraction processes in the plasma channel ensuring that the unstable diffractive rings of the circular case cannot be produced. The azimuthal modulational instability is thereby suppressed. These findings are verified by three-dimensional particle-in-cell simulations.

The generation and amplification of intergalactic magnetic fields in analogue laboratory experiments with high power lasers

Physics Reports Elsevier 601 (2015) 1-34

G Gregori, B Reville, F Miniati

The advent of high-power laser facilities has, in the past two decades, opened a new field of research where astrophysical environments can be scaled down to laboratory dimensions, while preserving the essential physics. This is due to the invariance of the equations of magneto-hydrodynamics to a class of similarity transformations. Here we review the relevant scaling relations and their application in laboratory astrophysics experiments with a focus on the generation and amplification of magnetic fields at cosmological shock waves. These arise during the collapse of protogalactic structures, resulting in the formation of high Mach number shocks in the intergalactic medium, which act as sources of vorticity in protogalaxies. The standard model for the origin of magnetic fields is via baroclinic generation from the resulting misaligned pressure and temperature gradients (the so-called Biermann battery process). While both experiment and numerical simulation have confirmed the occurrence of this mechanism at shocks, reconciling the resulting weak fields with present day observations is an un-solved problem, although it is generally accepted that turbulent motions of the weakly magnetised plasma plays a key role. Bridging the vast scale differences is a challenge both numerically and experimentally. A summary of novel laboratory experiments aimed at investigating additional processes that may shed light on these and other processes, such us turbulent amplification, resistive and collision-less plasma instabilities will be discussed in this review, particularly in relation to experiments using high power laser systems. The connection between laboratory shock waves and additional mechanisms, such as diffusive shock acceleration will be discussed. Finally, we will summarize the impact of laboratory investigation in furthering our understanding of plasma physics on super-galactic scales.

Self-consistent inclusion of classical large-angle Coulomb collisions in plasma Monte Carlo simulations


AE Turrell, M Sherlock, SJ Rose

X-ray free-electron laser studies of dense plasmas


SM Vinko