Transition from Collisional to Collisionless Regimes in Interpenetrating Plasma Flows on the National Ignition Facility.

Physical review letters 118 (2017) 185003-

JS Ross, DP Higginson, D Ryutov, F Fiuza, R Hatarik, CM Huntington, DH Kalantar, A Link, BB Pollock, BA Remington, HG Rinderknecht, GF Swadling, DP Turnbull, S Weber, S Wilks, DH Froula, MJ Rosenberg, T Morita, Y Sakawa, H Takabe, RP Drake, C Kuranz, G Gregori, J Meinecke, MC Levy, M Koenig, A Spitkovsky, RD Petrasso, CK Li, H Sio, B Lahmann, AB Zylstra, H-S Park

A study of the transition from collisional to collisionless plasma flows has been carried out at the National Ignition Facility using high Mach number (M>4) counterstreaming plasmas. In these experiments, CD-CD and CD-CH planar foils separated by 6-10 mm are irradiated with laser energies of 250 kJ per foil, generating ∼1000  km/s plasma flows. Varying the foil separation distance scales the ion density and average bulk velocity and, therefore, the ion-ion Coulomb mean free path, at the interaction region at the midplane. The characteristics of the flow interaction have been inferred from the neutrons and protons generated by deuteron-deuteron interactions and by x-ray emission from the hot, interpenetrating, and interacting plasmas. A localized burst of neutrons and bright x-ray emission near the midpoint of the counterstreaming flows was observed, suggesting strong heating and the initial stages of shock formation. As the separation of the CD-CH foils increases we observe enhanced neutron production compared to particle-in-cell simulations that include Coulomb collisions, but do not include collective collisionless plasma instabilities. The observed plasma heating and enhanced neutron production is consistent with the initial stages of collisionless shock formation, mediated by the Weibel filamentation instability.

Magnetic field production via the Weibel instability in interpenetrating plasma flows

PHYSICS OF PLASMAS 24 (2017) ARTN 041410

CM Huntington, MJ-E Manuel, JS Ross, SC Wilks, F Fiuza, HG Rinderknecht, H-S Park, G Gregori, DP Higginson, J Park, BB Pollock, BA Remington, DD Ryutov, C Ruyer, Y Sakawa, H Sio, A Spitkovsky, GF Swadling, H Takabe, AB Zylstra

Implementation of Hydrodynamic Simulation Code in Shock Experiment Design for Alkali Metals


AL Coleman, R Briggs, MG Gorman, S Ali, A Lazicki, DC Swift, PG Stubley, EE McBride, G Collins, JS Wark, MI McMahon, IOP

Phase transitions in shock compressed bismuth identified using single photon energy dispersive X-ray diffraction (SPEDX)


R Briggs, MJ Suggit, MG Gorman, A Coleman, R Heathcote, A Higginbotham, S Patel, JS Wark, MI McMahon, IOP

Nonlinear parametric resonance of relativistic electrons with a linearly polarized laser pulse in a plasma channel

Physics of Plasmas American Institute of Physics 24 (2017) 043105-

TW Huang, CT Zhou, APL Robinson, B Qiao, AV Arefiev, P Norreys, XT He, SC Ruan

The direct laser-acceleration mechanism, nonlinear parametric resonance, of relativistic electrons in a linearly polarized laser-produced plasma channel is examined by a self-consistent model including the relativistic laser dispersion in plasmas. Nonlinear parametric resonance can be excited, and the oscillation amplitude of electrons grows exponentially when the betatron frequency of electron motion varies roughly twice the natural frequency of the oscillator. It is shown analytically that the region of parametric resonance is defined by the self-similar parameter ne/nca0. The width of this region decreases with ne/nca0, but the energy gain and oscillation amplitude increases. In this regime, the electron transverse momentum grows faster than that in the linear classical resonance regime.

Atomic processes modeling of X-ray free electron laser produced plasmas using SCFLY code


H-K Chung, BI Cho, O Ciricosta, SM Vinko, JS Wark, RW Lee

Machine learning applied to proton radiography of high-energy-density plasmas

Physical Review E American Physical Society 95 (2017) 043305-

L Ceurvorst, N Ratan, J Sadler, MC Levy, R Trines, R Bingham, P Norreys, NFY Chen, MF Kasim

Proton radiography is a technique extensively used to resolve magnetic field structures in high-energy-density plasmas, revealing a whole variety of interesting phenomena such as magnetic reconnection and collisionless shocks found in astrophysical systems. Existing methods of analyzing proton radiographs give mostly qualitative results or specific quantitative parameters, such as magnetic field strength, and recent work showed that the line-integrated transverse magnetic field can be reconstructed in specific regimes where many simplifying assumptions were needed. Using artificial neural networks, we demonstrate for the first time 3D reconstruction of magnetic fields in the nonlinear regime, an improvement over existing methods, which reconstruct only in 2D and in the linear regime. A proof of concept is presented here, with mean reconstruction errors of less than 5% even after introducing noise. We demonstrate that over the long term, this approach is more computationally efficient compared to other techniques. We also highlight the need for proton tomography because (i) certain field structures cannot be reconstructed from a single radiograph and (ii) errors can be further reduced when reconstruction is performed on radiographs generated by proton beams fired in different directions.

Numerical modeling of laser-driven experiments aiming to demonstrate magnetic field amplification via turbulent dynamo

PHYSICS OF PLASMAS 24 (2017) ARTN 041404

P Tzeferacos, A Rigby, A Bott, AR Bell, R Bingham, A Casner, F Cattaneo, EM Churazov, J Emig, N Flocke, F Fiuza, CB Forest, J Foster, C Graziani, J Katz, M Koenig, C-K Li, J Meinecke, R Petrasso, H-S Park, BA Remington, JS Ross, D Ryu, D Ryutov, K Weide, TG White, B Reville, F Miniati, AA Schekochihin, DH Froula, G Gregori, DQ Lamb

Quantitative shadowgraphy and proton radiography for large intensity modulations.

Physical review. E 95 (2017) 023306-

MF Kasim, L Ceurvorst, N Ratan, J Sadler, N Chen, A Sävert, R Trines, R Bingham, PN Burrows, MC Kaluza, P Norreys

Shadowgraphy is a technique widely used to diagnose objects or systems in various fields in physics and engineering. In shadowgraphy, an optical beam is deflected by the object and then the intensity modulation is captured on a screen placed some distance away. However, retrieving quantitative information from the shadowgrams themselves is a challenging task because of the nonlinear nature of the process. Here, we present a method to retrieve quantitative information from shadowgrams, based on computational geometry. This process can also be applied to proton radiography for electric and magnetic field diagnosis in high-energy-density plasmas and has been benchmarked using a toroidal magnetic field as the object, among others. It is shown that the method can accurately retrieve quantitative parameters with error bars less than 10%, even when caustics are present. The method is also shown to be robust enough to process real experimental results with simple pre- and postprocessing techniques. This adds a powerful tool for research in various fields in engineering and physics for both techniques.

A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics.

Nature communications 8 (2017) 14125-

P Mabey, S Richardson, TG White, LB Fletcher, SH Glenzer, NJ Hartley, J Vorberger, DO Gericke, G Gregori

The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.

Simulations of the inelastic response of silicon to shock compression


PG Stubley, A Higginbotham, JS Wark

Optimization of plasma amplifiers.

Physical review. E 95 (2017) 053211-

JD Sadler, RMGM Trines, M Tabak, D Haberberger, DH Froula, AS Davies, S Bucht, LO Silva, EP Alves, F Fiúza, L Ceurvorst, N Ratan, MF Kasim, R Bingham, PA Norreys

Plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities. We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found to maintain good transverse coherence and high-energy efficiency. Effective compression of a 10kJ, nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier.

Robustness of raman plasma amplifiers and their potential for attosecond pulse generation

High Energy Density Physics Elsevier 23 (2017) 212–216-

JD Sadler, M Sliwa, T Miller, MF Kasim, N Ratan, L Ceurvorst, A Savin, R Aboushelbaya, P Norreys, D Haberberger, AS Davies, S Bucht, DH Froula, J Vieira, RA Fonseca, LO Silva, R Bingham, K Glize, RMGM Trines

Raman back-scatter from an under-dense plasma can be used to compress laser pulses, as shown by several previous experiments in the optical regime. A short seed pulse counter-propagates with a longer pump pulse and energy is transferred to the shorter pulse via stimulated Raman scattering. The robustness of the scheme to non-ideal plasma density conditions is demonstrated through particle-in-cell simulations. The scale invariance of the scheme ensures that compression of XUV pulses from a free electron laser is also possible, as demonstrated by further simulations. The output is as short as 300 as, with energy typical of fourth generation sources.

Measurements of plasma spectra from hot dense elements and mixtures at conditions relevant to the solar radiative zone.


DJ Hoarty, E Hill, P Beiersdorfer, P Allan, CRD Brown, MP Hill, LMR Hobbs, SF James, J Morton, N Sircombe, L Upcraft, JWO Harris, R Shepherd, E Marley, E Magee, J Emig, J Nilsen, SJ Rose

High flux, beamed neutron sources employing deuteron-rich ion beams from D<inf>2</inf>O-ice layered targets

Plasma Physics and Controlled Fusion 59 (2017)

A Alejo, AG Krygier, H Ahmed, JT Morrison, RJ Clarke, J Fuchs, A Green, JS Green, D Jung, A Kleinschmidt, Z Najmudin, H Nakamura, P Norreys, M Notley, M Oliver, M Roth, L Vassura, M Zepf, M Borghesi, RR Freeman, S Kar

© 2017 IOP Publishing Ltd. A forwardly-peaked bright neutron source was produced using a laser-driven, deuteron-rich ion beam in a pitcher-catcher scenario. A proton-free ion source was produced via target normal sheath acceleration from Au foils having a thin layer of D2O ice at the rear side, irradiated by sub-petawatt laser pulses (∼200 J, ∼750 fs) at peak intensity . The neutrons were preferentially produced in a beam of ∼70 FWHM cone along the ion beam forward direction, with maximum energy up to ∼40 MeV and a peak flux along the axis for neutron energy above 2.5 MeV. The experimental data is in good agreement with the simulations carried out for the d(d,n)3He reaction using the deuteron beam produced by the ice-layered target.

Ultrafast X-Ray Diffraction Studies of the Phase Transitions and Equation of State of Scandium Shock Compressed to 82 GPa.

Physical review letters 118 (2017) 025501-

R Briggs, MG Gorman, AL Coleman, RS McWilliams, EE McBride, D McGonegle, JS Wark, L Peacock, S Rothman, SG Macleod, CA Bolme, AE Gleason, GW Collins, JH Eggert, DE Fratanduono, RF Smith, E Galtier, E Granados, HJ Lee, B Nagler, I Nam, Z Xing, MI McMahon

Using x-ray diffraction at the Linac Coherent Light Source x-ray free-electron laser, we have determined simultaneously and self-consistently the phase transitions and equation of state (EOS) of the lightest transition metal, scandium, under shock compression. On compression scandium undergoes a structural phase transition between 32 and 35 GPa to the same bcc structure seen at high temperatures at ambient pressures, and then a further transition at 46 GPa to the incommensurate host-guest polymorph found above 21 GPa in static compression at room temperature. Shock melting of the host-guest phase is observed between 53 and 72 GPa with the disappearance of Bragg scattering and the growth of a broad asymmetric diffraction peak from the high-density liquid.

High Orbital Angular Momentum Harmonic Generation

Physical Review Letters 117 (2016)

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

© 2016 American Physical Society. We identify and explore a high orbital angular momentum (OAM) harmonics generation and amplification mechanism that manipulates the OAM independently of any other laser property, by preserving the initial laser wavelength, through stimulated Raman backscattering in a plasma. The high OAM harmonics spectra can extend at least up to the limiting value imposed by the paraxial approximation. We show with theory and particle-in-cell simulations that the orders of the OAM harmonics can be tuned according to a selection rule that depends on the initial OAM of the interacting waves. We illustrate the high OAM harmonics generation in a plasma using several examples including the generation of prime OAM harmonics. The process can also be realized in any nonlinear optical Kerr media supporting three-wave interactions.

Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet.

Nature communications 7 (2016) 13081-

CK Li, P Tzeferacos, D Lamb, G Gregori, PA Norreys, MJ Rosenberg, RK Follett, DH Froula, M Koenig, FH Seguin, JA Frenje, HG Rinderknecht, H Sio, AB Zylstra, RD Petrasso, PA Amendt, HS Park, BA Remington, DD Ryutov, SC Wilks, R Betti, A Frank, SX Hu, TC Sangster, P Hartigan, RP Drake, CC Kuranz, SV Lebedev, NC Woolsey

The remarkable discovery by the Chandra X-ray observatory that the Crab nebula's jet periodically changes direction provides a challenge to our understanding of astrophysical jet dynamics. It has been suggested that this phenomenon may be the consequence of magnetic fields and magnetohydrodynamic instabilities, but experimental demonstration in a controlled laboratory environment has remained elusive. Here we report experiments that use high-power lasers to create a plasma jet that can be directly compared with the Crab jet through well-defined physical scaling laws. The jet generates its own embedded toroidal magnetic fields; as it moves, plasma instabilities result in multiple deflections of the propagation direction, mimicking the kink behaviour of the Crab jet. The experiment is modelled with three-dimensional numerical simulations that show exactly how the instability develops and results in changes of direction of the jet.

Numerical study of neutron beam divergence in a beam-fusion scenario employing laser driven ions


A Alejo, A Green, H Ahmed, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, P McKenna, SR Mirfayzi, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi, S Kar

Raman scattering for intense high orbital angular momentum harmonic generation

2016 Conference on Lasers and Electro-Optics, CLEO 2016 (2016)

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

© 2016 OSA. We identify a mechanism, based on Raman scattering, to endow near-infrared laser beams with high orders of orbital angular momentum (OAM). In combination with high-harmonic generation, this could lead to very high OAM harmonics in the soft x-ray region.