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

Journal of Physics: Conference Series IOP Publishing: Conference Series 688 (2016) 012098-

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, K Zhang, J Zhong, F Wang, H Takabe

One of the important and interesting problems in astrophysics and plasma physics is collimation of plasma jets. The collimation mechanism, which causes a plasma flow to propagate a long distance, has not been understood in detail. We have been investigating a model experiment to simulate astrophysical plasma jets with an external magnetic field [Nishio et al., EPJ. Web of Conferences 59, 15005 (2013)]. The experiment was performed by using Gekko XII HIPER laser system at Institute of Laser Engineering, Osaka University. We shot CH plane targets (3 mm × 3 mm × 10 μm) and observed rear-side plasma flows. A collimated plasma flow or plasma jet was generated by separating focal spots of laser beams. In this report, we measured plasma jet structure without an external magnetic field with shadowgraphy, and simultaneously measured the local parameters of the plasma jet, i.e., electron density, electron and ion temperatures, charge state, and drift velocity, with collective Thomson scattering.

Spherical shock in the presence of an external magnetic field

Journal of Physics: Conference Series IOP Publishing: Conference Series 688 (2016) 012056-

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, CL Yin, YT Li, K Zhang, H Takabe

We investigate spherical collisionless shocks in the presence of an external magnetic field. Spherical collisionless shocks are common resultant of interactions between a expanding plasma and a surrounding plasma, such as the solar wind, stellar winds, and supernova remnants. Anisotropies often observed in shock propagations and their emissions, and it is widely believed a magnetic field plays a major role. Since the local observations of magnetic fields in astrophysical plasmas are not accessible, laboratory experiments provide unique capability to investigate such phenomena. We model the spherical shocks in the universe by irradiating a solid spherical target surrounded by a plasma in the presence of a magnetic field. We present preliminary results obtained by shadowgraphy.

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.

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) 8–13 September 2013, Nara, Japan IOP Publishing Ltd. 688 (2016) 012071-012071
Part of a series from Journal of Physics: Conference Series

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 Quirós, BA Remington, B Reville, JS Ross, N Woolsey, HS Park

We report the measurements of electrostatic field structures associated with an electrostatic shock formed in laser-produced counter-streaming plasmas with proton imaging. The thickness of the electrostatic structure is estimated from proton images with different proton kinetic energies from 4.7 MeV to 10.7 MeV. The width of the transition region is characterized by electron scale length in the laser-produced plasma, suggesting that the field structure is formed due to a collisionless electrostatic shock.

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.

A laboratory model of post-Newtonian gravity with high power lasers and 4th generation light sources


G Gregori, MC Levy, MA Wadud, BJB Crowley, R Bingham

Inelastic response of silicon to shock compression.

Scientific reports Nature Publishing Group 6 (2016) 24211-

A Higginbotham, PG Stubley, AJ Comley, JH Eggert, JM Foster, DH Kalantar, D McGonegle, S Patel, LJ Peacock, SD Rothman, RF Smith, MJ Suggit, J Wark

The elastic and inelastic response of [001] oriented silicon to laser compression has been a topic of considerable discussion for well over a decade, yet there has been little progress in understanding the basic behaviour of this apparently simple material. We present experimental x-ray diffraction data showing complex elastic strain profiles in laser compressed samples on nanosecond timescales. We also present molecular dynamics and elasticity code modelling which suggests that a pressure induced phase transition is the cause of the previously reported 'anomalous' elastic waves. Moreover, this interpretation allows for measurement of the kinetic timescales for transition. This model is also discussed in the wider context of reported deformation of silicon to rapid compression in the literature.

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

Nature Communications Nature Publishing Group 7 (2016) ncomms11899-

JE Cross, G Gregori, JM Foster, P Graham, JM 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.

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

Nature Communications Nature Publishing 7 (2016) Article 10371-

J Vieira, RMGM Trines, EP Alves, RA Fonseca, JT Mendon�a, 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.

Efficient evaluation of collisional energy transfer terms for plasma particle simulations


AE Turrell, M Sherlock, SJ Rose

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.

AWAKE: A Proton-Driven Plasma Wakefield Acceleration Experiment at CERN

Nuclear and Particle Physics Proceedings Elsevier (2016)

C Bracco, LD Amorim, R Assmann, F Batsch, R Bingham, G Burt, B Buttenschön, A Butterworth, A Caldwell, S Chattopadhyay, S Cipiccia, LC Deacon, S Doebert, U Dorda, E Feldbaumer, RA Fonseca, V Fedossev, B Goddard, J Grebenyuk, O Grulke, E Gschwendtner, J Hansen, C Hessler, W Hofle, J Holloway

© 2015 Elsevier B.V..The AWAKE Collaboration has been formed in order to demonstrate proton-driven plasma wakefield acceleration for the first time. This acceleration technique could lead to future colliders of high energy but of a much reduced length when compared to proposed linear accelerators. The CERN SPS proton beam in the CNGS facility will be injected into a 10 m plasma cell where the long proton bunches will be modulated into significantly shorter micro-bunches. These micro-bunches will then initiate a strong wakefield in the plasma with peak fields above 1 GV/m that will be harnessed to accelerate a bunch of electrons from about 20 MeV to the GeV scale within a few meters. The experimental program is based on detailed numerical simulations of beam and plasma interactions. The main accelerator components, the experimental area and infrastructure required as well as the plasma cell and the diagnostic equipment are discussed in detail. First protons to the experiment are expected at the end of 2016 and this will be followed by an initial three-four years experimental program. The experiment will inform future larger-scale tests of proton-driven plasma wakefield acceleration and applications to high energy colliders.

Mitigating the hosing instability in relativistic laser-plasma interactions

New Journal of Physics Institute of Physics 18 (2016) 053023-

L Ceurvorst, N Ratan, MC Levy, M Kasim, J Sadler, RHH Scott, RMGM Trines, TW Huang, M Skramic, M Vranic, LO Silva, PA Norreys

A new physical model of the hosing instability that includes relativistic laser pulses and moderate densities is presented and derives the density dependence of the hosing equation. This is tested against two-dimensional particle-in-cell simulations. These simulations further examine the feasibility of using multiple pulses to mitigate the hosing instability in a Nd:glass-type parameter space. An examination of the effects of planar versus cylindrical exponential density gradients on the hosing instability is also presented. The results show that strongly relativistic pulses and more planar geometries are capable of mitigating the hosing instability which is in line with the predictions of the physical model.

Characteristics of betatron radiation from direct-laser accelerated electrons

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics American Physical Society 93 (2016) 063203

TW Huang, APL Robinson, C-T Zhou, B Qiao, B Liu, R Shang-Chen, H Xian-Tu, P Norreys

Betatron radiation from direct-laser accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S(≡ne/nca0). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a0) for a fixed value of S. As a result, the total number of radiated photons scales as a2/0/√S and the energy conversion efficiency of photons from the accelerated electrons scales as a3/0/S. The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.

Beamed neutron emission driven by laser accelerated light ions

New Journal of Physics IOP Publishing (2016)

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

Highly anisotropic, beam-like neutron emission with peak flux of the order of 109 n/sr was obtained from light nuclei reactions in a pitcher–catcher scenario, by employing MeV ions driven by a sub-petawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of $\sim 70^\circ $, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher–catcher materials indicates the dominant reactions being d(p, n+p)1H and d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles is most likely related to the directionality and high energy of the projectile ions.

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

Sherlock et al. Reply

Physical Review Letters American Physical Society 116 (2016)

S Rose, M Sherlock, W Rozmus, EG Hill

Theory of Thomson scattering in inhomogeneous media

Scientific reports Nature Publishing Group 6 (2016) 24283-

PM Kozlowski, BJ Crowley, 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.

Measurements of continuum lowering in solid-density plasmas created from elements and compounds

Nature Communications Nature Publishing Group 7 (2016) 11713-

O Ciricosta, SM Vinko, JS Wark, B Barbrel, DS Rackstraw, TR Preston, J Chalupsky, B Cho, H-K Chung, GL Dakovski, K Engelhorn, V Hajkova, P Heimann, M Holmes, L Juha, J Krzywinski, RW Lee, S Toleikis, JJ Turner, U Zastrau, T Burian

The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.

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.