Publications by Gianluca Gregori


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


Interaction of a highly radiative shock with a solid obstacle

PHYSICS OF PLASMAS 24 (2017) ARTN 082707

M Koenig, T Michel, R Yurchak, C Michaut, B Albertazzi, S Laffite, E Falize, LVB Som, Y Sakawa, T Sano, Y Hara, T Morita, Y Kuramitsu, P Barroso, A Pelka, G Gregori, R Kodama, N Ozaki, D Lamb, P Tzeferacos


Time evolution and asymmetry of a laser produced blast wave

PHYSICS OF PLASMAS 24 (2017) ARTN 103124

ER Tubman, RHH Scott, HW Doyle, J Meinecke, H Ahmed, RAB Alraddadi, R Bolis, JE Cross, R Crowston, D Doria, D Lamb, B Reville, APL Robinson, P Tzeferacos, M Borghesi, G Gregori, NC Woolsey


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


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.


Identifying deformation mechanisms in molecular dynamics simulations of laser shocked matter

JOURNAL OF COMPUTATIONAL PHYSICS 350 (2017) 16-24

TG White, A Tikku, MFA Silva, G Gregori, A Higginbotham, DE Eakins


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.


Thomson scattering measurement of a collimated plasma jet generated by a high-power laser system

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 (2016)

T Ishikawa, Y Sakawa, T Morita, Y Yamaura, Y Kuramitsu, T Moritaka, T Sano, R Shimoda, K Tomita, K Uchino, S Matsukiyo, A Mizuta, N Ohnishi, R Crowston, N Woolsey, H Doyle, G Gregori, M Koenig, C Michaut, A Pelka, D Yuan, Y Li, K Zhang, J Zhong, F Wang, H Takabe, IOP


Spherical shock in the presence of an external magnetic field

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 (2016)

Y Kuramitsu, S Matsukiyo, S Isayama, D Harada, T Oyama, R Fujino, Y Sakawa, T Morita, Y Yamaura, T Ishikawa, T Moritaka, T Sano, K Tomita, R Shimoda, Y Sato, K Uchino, A Pelka, R Crowston, N Woolsey, G Gregori, M Koenig, DW Yuan, CL Yin, YT Li, K Zhang, JY Zhong, FL Wang, N Ohnishi, K Nagamine, H Yoneda, H Takabe, IOP


Laboratory astrophysical collisionless shock experiments on Omega and NIF

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 (2016)

H-S 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, AB Zylstra, IOP


Proton imaging of an electrostatic field structure formed in laser-produced counter-streaming plasmas

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 (2016)

T Morita, NL Kugland, W Wan, R Crowston, RP Drake, F Fiuza, G Gregori, C Huntington, T Ishikawa, M Koenig, C Kuranz, MC Levy, D Martinez, J Meinecke, F Miniati, CD Murphy, A Pelka, C Plechaty, R Presura, N Quiros, BA Remington, B Reville, JS Ross, DD Ryutov, Y Sakawa, L Steele, H Takabe, Y Yamaura, N Woolsey, H-S Park, IOP


Laboratory analogue of a supersonic accretion column in a binary star system.

Nature communications 7 (2016) ncomms11899-

JE Cross, G Gregori, JM Foster, P Graham, J-M Bonnet-Bidaud, C Busschaert, N Charpentier, CN Danson, HW Doyle, RP Drake, J Fyrth, ET Gumbrell, M Koenig, C Krauland, CC Kuranz, B Loupias, C Michaut, M Mouchet, S Patankar, J Skidmore, C Spindloe, ER Tubman, N Woolsey, R Yurchak, É Falize

Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy-gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100-1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.


Short-pulse laser-driven x-ray radiography

HIGH POWER LASER SCIENCE AND ENGINEERING 4 (2016) ARTN e30

E Brambrink, S Baton, M Koenig, R Yurchak, N Bidaut, B Albertazzi, JE Cross, G Gregori, A Rigby, E Falize, A Pelka, F Kroll, S Pikuz, Y Sakawa, N Ozaki, C Kuranz, M Manuel, C Li, P Tzeferacos, D Lamb


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

PHYSICS OF PLASMAS 23 (2016) ARTN 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 Diziere, M Koenig, N Woolsey, Y Matsumoto, A Mizuta, T Sugiyama, S Matsukiyo, T Moritaka, T Sano, H Takabe


Nanosecond formation of diamond and lonsdaleite by shock compression of graphite.

Nature communications 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 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.


Dynamic X-ray diffraction observation of shocked solid iron up to 170 GPa.

Proceedings of the National Academy of Sciences of the United States of America 113 (2016) 7745-7749

A Denoeud, N Ozaki, A Benuzzi-Mounaix, H Uranishi, Y Kondo, R Kodama, E Brambrink, A Ravasio, M Bocoum, J-M Boudenne, M Harmand, F Guyot, S Mazevet, D Riley, M Makita, T Sano, Y Sakawa, Y Inubushi, G Gregori, M Koenig, G Morard

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.


Experimental measurements of the collisional absorption of XUV radiation in warm dense aluminium.

Physical review. E 94 (2016) 023203-

B Kettle, T Dzelzainis, S White, L Li, B Dromey, M Zepf, CLS Lewis, G Williams, S Künzel, M Fajardo, H Dacasa, P Zeitoun, A Rigby, G Gregori, C Spindloe, R Heathcote, D Riley

The collisional (or free-free) absorption of soft x rays in warm dense aluminium remains an unsolved problem. Competing descriptions of the process exist, two of which we compare to our experimental data here. One of these is based on a weak scattering model, another uses a corrected classical approach. These two models show distinctly different behaviors with temperature. Here we describe experimental evidence for the absorption of 26-eV photons in solid density warm aluminium (T_{e}≈1 eV). Radiative x-ray heating from palladium-coated CH foils was used to create the warm dense aluminium samples and a laser-driven high-harmonic beam from an argon gas jet provided the probe. The results indicate little or no change in absorption upon heating. This behavior is in agreement with the prediction of the corrected classical approach, although there is not agreement in absolute absorption value. Verifying the correct absorption mechanism is decisive in providing a better understanding of the complex behavior of the warm dense state.


Theory of Thomson scattering in inhomogeneous media.

Scientific Reports 6 (2016) 24283-

PM Kozlowski, BJB Crowley, DO Gericke, SP Regan, G Gregori

Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems.

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