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In 2021 the Quantum Sensors for the Hidden Sector (QSHS) collaboration was founded in the UK. We received funding as part of the Quantum Technologies for Fundamental Physics programme to develop and demonstrate quantum devices with the potential to detect hidden-sector particles such as axions and dark photons in the ~1μeV/c^2 to ~100μeV/c^2 mass window. Our collaboration is formed from a diverse community of condensed matter physicists, quantum technologists, theorists and (astro) particle physics experimentalists. We are designing and fabricating a range of “quantum devices” and constructing a high-field, low-temperature facility at the University of Sheffield to characterise and test the devices in an axion haloscope geometry, initially using an rf cavity. This poster was presented at the 17th Patras workshop on axions, WIMPs and WISPs on the 8th August 2022 in Mainz, Germany.

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks are observed to amplify magnetic fields1 and accelerate electrons and protons to highly relativistic speeds2–4. In the well-established model of diffusive shock acceleration5, relativistic particles are accelerated by repeated shock crossings. However, this requires a separate mechanism that pre-accelerates particles to enable shock crossing. This is known as the ‘injection problem’, which is particularly relevant for electrons, and remains one of the most important puzzles in shock acceleration6. In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism. Here we report results from laser-driven plasma flow experiments, and related simulations, that probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. We show that electrons can be effectively accelerated in a first-order Fermi process by small-scale turbulence produced within the shock transition to relativistic non-thermal energies, helping overcome the injection problem. Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators. In laser–plasma experiments complemented by simulations, electron acceleration is observed in turbulent collisionless shocks. This work clarifies the pre-acceleration to relativistic energies required for the onset of diffusive shock acceleration.

Turbulence is ubiquitous in the universe and in fluid dynamics. It influences a wide range of high energy density systems, from inertial confinement fusion to astrophysical-object evolution. Understanding this phenomenon is crucial, however, due to limitations in experimental and numerical methods in plasma systems, a complete description of the turbulent spectrum is still lacking. Here, we present the measurement of a turbulent spectrum down to micron scale in a laser-plasma experiment. We use an experimental platform, which couples a high power optical laser, an x-ray free-electron laser and a lithium fluoride crystal, to study the dynamics of a plasma flow with micrometric resolution (~1μm) over a large field of view (>1 mm2). After the evolution of a Rayleigh–Taylor unstable system, we obtain spectra, which are overall consistent with existing turbulent theory, but present unexpected features. This work paves the way towards a better understanding of numerous systems, as it allows the direct comparison of experimental results, theory and numerical simulations. Turbulence effects explored use macroscale systems in general. Here the authors generate a turbulent plasma using laser irradiation of a solid target and study the dynamics of the plasma flow at the micron-scale by using scattering of an XFEL beam.

We investigate the two-dimensional motion of relativistic cold electrons in the presence of `strictly' spatially varying magnetic fields satisfying, however, no magnetic monopole condition. We find that the degeneracy of Landau levels, which arises in the case of the constant magnetic field, lifts out when the field is variable and the energy levels of spin-up and spin-down electrons align in an interesting way depending on the nature of change of field. Also the varying magnetic field splits Landau levels of electrons with zero angular momentum from positive angular momentum, unlike the constant field which only can split the levels between positive and negative angular momenta. Exploring Landau quantization in non-uniform magnetic fields is a unique venture on its own and has interdisciplinary implications in the fields ranging from condensed matter to astrophysics to quantum information. As examples, we show magnetized white dwarfs, with varying magnetic fields, involved simultaneously with Lorentz force and Landau quantization affecting the underlying degenerate electron gas, exhibiting a significant violation of the Chandrasekhar mass-limit; and an increase in quantum speed of electrons in the presence of a spatially growing magnetic field., Comment: 30 pages including 12 figures; accepted for publication in SciPost Physics

By taking the spatial and temporal Fourier transforms of the coordinates of the atoms in molecular dynamics simulations conducted using an embedded-atom-method potential, we calculate the inelastic scattering of x-rays from copper singlecrystals shocked along [001] to pressures of up to 70 GPa. Above the Hugoniot elastic limit (HEL), we find that the copious stacking faults generated at the shock front introduce strong quasi-elastic scattering (QES) that competes with the inelastic scattering signal, which remains discernible within the first Brillouin zone; for specific directions in reciprocal space outside the first zone, the QES dominates the inelastic signal overwhelmingly. The synthetic scattering spectra we generate from our Fourier transforms suggest that energy resolutions of order 10 meV would be required to distinguish inelastic from quasi-elastic scattering within the first Brillouin zone of shock-loaded copper. We further note that high-resolution inelastic scattering also affords the possibility of directly measuring particle velocities via the Doppler shift. These simulations are of relevance to future planned inelastic scattering experiments at x-ray Free Electron Laser (FEL) facilities.

Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled magnetic field whose energy is close to equipartition with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time \cite{cowie1977,fabian1994}. While feedback from the central active galactic nuclei (AGN) \cite{fabian2012,birzan2012,churazov2000} is believed to provide most of the heating, there has been a long debate as to whether conduction of heat from the bulk to the core can help the core to reach the observed temperatures \cite{narayan2001,ruszkowski2002,kunz2011}, given the presence of tangled magnetic fields. Interestingly, evidence of very sharp temperature gradients in structures like cold fronts implies a high degree of suppression of thermal conduction \cite{markevitch2007}. To address the problem of thermal conduction in a magnetized and turbulent plasma, we have created a replica of such a system in a laser laboratory experiment. Our data show a reduction of local heat transport by two orders of magnitude or more, leading to strong temperature variations on small spatial scales, as is seen in cluster plasmas \cite{markevitch2003}.

Review of scientific instruments 92(3), 039901 (2021). doi:10.1063/5.0043951, This article was originally published online on 4 January 2021 with an error in the title and Ref. 6 should have been deleted from the reference section and the text. The title is correct above. All online and printed versions of the article were corrected on 7 January 2021. AIP Publishing apologizes for this error., Published by American Institute of Physics, [S.l.]

An x-ray radiography technique based upon phase contrast imaging using a lithium fluoride detector has been demonstrated for goals of high energy density physics experiments. Based on the simulation of propagation an x-ray free-electron laser beam through a test-object, the visibility of phase-contrast image depending on an object-detector distance was investigated. Additionally, the metrological capabilities of a lithium fluoride crystal as a detector were demonstrated.

Review of scientific instruments 92(1), 013101 (2021). doi:10.1063/5.0022886, We introduce a setup to measure high-resolution inelastic x-ray scattering at the High Energy Density scientific instrument at the European X-Ray Free-Electron Laser (XFEL). The setup uses the Si (533) reflection in a channel-cut monochromator and three spherical diced analyzer crystals in near-backscattering geometry to reach a high spectral resolution. An energy resolution of 44 meV is demonstrated for the experimental setup, close to the theoretically achievable minimum resolution. The analyzer crystals and detector are mounted on a curved-rail system, allowing quick and reliable changes in scattering angle without breaking vacuum. The entire setup is designed for operation at 10 Hz, the same repetition rate as the high-power lasers available at the instrument and the fundamental repetition rate of the European XFEL. Among other measurements, it is envisioned that this setup will allow studies of the dynamics of highly transient laser generated states of matter., Published by American Institute of Physics, [S.l.]

The paper investigates the aviation sector, as a case in point for a Smart environment and as an example for Industry 5.0 and Society 5.0 purposes. In the smart complex environments, a systemic vision of the elements, which act and are acted within a given territory, should be the basis of a hypothesis of joint growth. Indeed, the synergies activated by the system can be seen as the product of the application of a particular knowledge-based open innovation strategy, as an orientation capable of transforming theoretical assumptions into concrete operational innovation paths. Through the evidence emerged from an important case study and the application of an MCDA methodology, we have tried to identify which are the optimal solutions for the implementation of the new human-centric logics of I5.0, analyzing them on the basis of the actual benefits for the ecosystem, going beyond the self-referential aptitude of the firm to instill technological changes and managerial visions. Knowledge circulation, dialogue between sub-systems, and the ability to adapt technology and entrepreneurial strategies to the environment in which it operates (with the users as first stakeholders) seem to be necessary practices in knowledge-based innovation, prioritization, and decision-making processes, for smart, sustainable, and inclusive solutions.

We report a laser-plasma experiment that was carried out at the LMJ-PETAL facility and realized the first magnetized, turbulent, supersonic plasma with a large magnetic Reynolds number ($\mathrm{Rm} \approx 45$) in the laboratory. Initial seed magnetic fields were amplified, but only moderately so, and did not become dynamically significant. A notable absence of magnetic energy at scales smaller than the outer scale of the turbulent cascade was also observed. Our results support the notion that moderately supersonic, low-magnetic-Prandtl-number plasma turbulence is inefficient at amplifying magnetic fields., 6 pages, 4 figures; supplemental information included (14 pages, 10 figures)

Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-β plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes.

Scientific reports 10(1), 14564 (2020). doi:10.1038/s41598-020-71350-x, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

We investigate the prospect of an alternative laboratory-based search for the coupling of axions and axion-like particles to photons. Here, the collision of two laser beams resonantly produces axions, and a signal photon is detected after magnetic reconversion, as in light-shining-through-walls (LSW) experiments. Conventional searches, such as LSW or anomalous birefrigence measurements, are most sensitive to axion masses for which substantial coherence can be achieved; this is usually well below optical energies. We find that using currently available high-power laser facilities, the bounds that can be achieved by our approach outperform traditional LSW at axion masses between $0.5-6$ eV, set by the optical laser frequencies and collision angle. These bounds can be further improved through coherent scattering off laser substructures, probing axion-photon couplings down to $g_{a\gamma\gamma}\sim 10^{-8} {\text{GeV}^{-1}}$, comparable with existing CAST bounds. Assuming a day long measurement per angular step, the QCD axion band can be reached., Comment: 6 pages, 5 figures; realistic experimental parameters considered. To appear in PRD

Currently there is considerable interest in creating scalable laboratory plasmas to study the mechanisms behind the formation and evolution of astrophysical phenomena such as Herbig-Haro objects and supernova remnants. Laboratory-scaled experiments can provide a well diagnosed and repeatable supplement to direct observations of these extraterrestrial objects if they meet similarity criteria demonstrating that the same physics govern both systems. Here, we present a study on the role of collision and cooling rates on shock formation using colliding jets from opposed conical wire arrays on a compact pulsed-power driver. These diverse conditions were achieved by changing the wire material feeding the jets, since the ion-ion mean free path (λ_{mfp-ii}) and radiative cooling rates (P_{rad}) increase with atomic number. Low Z carbon flows produced smooth, temporally stable shocks. Weakly collisional, moderately cooled aluminum flows produced strong shocks that developed signs of thermal condensation instabilities and turbulence. Weakly collisional, strongly cooled copper flows collided to form thin shocks that developed inconsistently and fragmented. Effectively collisionless, strongly cooled tungsten flows interpenetrated, producing long axial density perturbations.

Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm} < 1$). However, the same framework proposes that the fluctuation dynamo should operate differently when $\mathrm{Pm} \gtrsim 1$, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports a new experiment that creates a laboratory $\mathrm{Pm} \gtrsim 1$ plasma dynamo for the first time. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude from its initial value and saturate dynamically. It is shown that the growth of these fields occurs exponentially at a rate that is much greater than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized MHD simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems., 12 pages, 9 figures

An experimental scheme is presented for generating low-divergence, ultradense, relativistic, electron-positron beams using 400 GeV/c protons available at facilities such as HiRadMat and AWAKE at CERN. Preliminary Monte Carlo and particle-in-cell simulations demonstrate the possibility of generating beams containing 1013–1014 electron-positron pairs at sufficiently high densities to drive collisionless beam-plasma instabilities, which are expected to play an important role in magnetic field generation and the related radiation signatures of relativistic astrophysical phenomena. The pair beams are quasineutral, with size exceeding several skin depths in all dimensions, allowing the examination of the effect of competition between transverse and longitudinal instability modes on the growth of magnetic fields. Furthermore, the presented scheme allows for the possibility of controlling the relative density of hadrons to electron-positron pairs in the beam, making it possible to explore the parameter spaces for different astrophysical environments. A previously unexplored experimental scheme is presented for generating low-divergence, ultra-dense, relativistic, electron-positron beams using 400 GeV/c protons available at facilities such as HiRadMat and AWAKE at CERN. Preliminary Monte-Carlo and Particle-in-cell simulations demonstrate the possibility of generating beams containing $10^{13}-10^{14}$ electron-positron pairs at sufficiently high densities to drive collisionless beam-plasma instabilities, which are expected to play an important role in magnetic field generation and the related radiation signatures of relativistic astrophysical phenomena. The pair beams are quasi-neutral, with size exceeding several skin-depths in all dimensions, allowing for the first time the examination of the effect of competition between transverse and longitudinal instability modes on the growth of magnetic fields. Furthermore, the presented scheme allows for the possibility of controlling the relative density of hadrons to electron-positron pairs in the beam, making it possible to explore the parameter spaces for different astrophysical environments.

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jet winds, etc.) is a common process which leads to a more intricate structure of the interstellar medium. In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNRs) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage, and the distance between the two stars. In this Letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BWs) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼500 J) of 300 μm diameter carbon rods and propagate in different gases (Ar and N2) at different pressures. The physical parameters, such as the density and temperature of the IR, are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy, etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17–20% increase in temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long periods after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.

The decay of a massive pseudoscalar, scalar and U(1) boson into an electron-positron pair in the presence of strong electromagnetic backgrounds is calculated. Of particular interest is the constant-crossed-field limit, relevant for experiments that aim to measure high-energy axion-like-particle conversion into electron-positron pairs in a magnetic field. The total probability depends on the quantum nonlinearity parameter - a product of field and lightfront momentum invariants. Depending on the seed particle mass, different decay regimes are identified. In the below-threshold case, we find the probability depends on a non-perturbative tunnelling exponent depending on the quantum parameter and the particle mass. In the above-threshold case, we find that when the quantum parameter is varied linearly, the probability oscillates nonlinearly around the spontaneous decay probability. A strong-field limit is identified in which the threshold is found to disappear. In modelling the fall-off of a quasi-constant-crossed magnetic field, we calculate probabilities beyond the constant limit and investigate when the decay probability can be regarded as locally constant., Comment: 22 pages, 7 figures

Our understanding of physical systems often depends on our ability to match complex computational modeling with the measured experimental outcomes. However, simulations with large parameter spaces suffer from inverse problem instabilities, where similar simulated outputs can map back to very different sets of input parameters. While of fundamental importance, such instabilities are seldom resolved due to the intractably large number of simulations required to comprehensively explore parameter space. Here, we show how Bayesian inference can be used to address inverse problem instabilities in the interpretation of x-ray emission spectroscopy and inelastic x-ray scattering diagnostics. We find that the extraction of information from measurements on the basis of agreement with simulations alone is unreliable and leads to a significant underestimation of uncertainties. We describe how to statistically quantify the effect of unstable inverse models and describe an approach to experimental design that mitigates its impact.

We develop a new approach to modeling many-body systems based on Bohm’s interpretation of quantum mechanics., Modeling many-body quantum systems with strong interactions is one of the core challenges of modern physics. A range of methods has been developed to approach this task, each with its own idiosyncrasies, approximations, and realm of applicability. However, there remain many problems that are intractable for existing methods. In particular, many approaches face a huge computational barrier when modeling large numbers of coupled electrons and ions at finite temperature. Here, we address this shortfall with a new approach to modeling many-body quantum systems. On the basis of the Bohmian trajectory formalism, our new method treats the full particle dynamics with a considerable increase in computational speed. As a result, we are able to perform large-scale simulations of coupled electron-ion systems without using the adiabatic Born-Oppenheimer approximation.

We consider the dynamics of a charged particle (e.g., an electron) oscillating in a laser field in flat spacetime and describe it in terms of the variable mass metric. By applying Einstein's equivalence principle, we show that, after representing the electron motion in a time-dependent manner, the variable mass metric takes the form of the Friedmann–Lemaitre–Robertson–Walker metric. We quantize a pseudo-scalar field in this spacetime and derive the production rate of electrically neutral, spinless particles. We show that this approach can provide an alternative experimental method to axion searches.

Background Transvaginal ultrasonography (TVS) and serum biomarkers are widely used in clinical practice to triage adnexal masses, but the effectiveness of current biomarkers is quite weak. Objectives To determine the best way to diagnose the patients with adnexal masses, in terms of diagnostic accuracy and economic costs, among four triage strategies: International Ovarian Tumor Analysis group's simple rules (SR) for the interpretation of TVS with the addition of subjective assessment (SA) by an experienced ultrasound operator only when TVS results are inconclusive (hereafter defined as SR±SA), SR±SA+CA125, SR±SA+HE4, and SR±SA+ROMA. Our main hypothesis was that the addition of the biomarkers (CA125, HE4 or ROMA algorithm) to SR±SA could improve the triage of these patients in terms of diagnostic accuracy (i.e., malignant versus benign). As secondary analyses we estimated the cost-effectiveness of the four strategies and the diagnostic accuracy of SR±SA at the study hospitals. Methods From February 2013 to January 2015, 447 consecutive patients who were scheduled for surgery for an adnexal mass at the S.Anna and Mauriziano Hospitals in Turin were enrolled in this multi-center prospective cohort study. Preoperative TVS was performed and preoperative CA125 and HE4 levels were measured. Pathology reports were used to assess the diagnostic accuracy of the four triage strategies, and the costs of each strategy were also calculated. Results 391 patients were included in the analysis: 57% (221) were premenopausal and 43% (170) were postmenopausal. The overall prevalence of malignancy was 21%. SR were conclusive in 89% of patients; the overall performance of SR±SA was: sensitivity 82%, specificity 92%, and positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio: 74%, 95%, 10.5, and 0.19, respectively. In premenopausal women, mean costs varied from €36.4 for SR±SA, to €70.1 for SR±SA+ROMA. The addition of biomarkers to SR±SA showed no diagnostic advantage compared to SR±SA and was also more costly. Among postmenopausal women, mean costs varied from €39.5 for SR±SA, to €73.2 for SR±SA+ROMA. SR±SA+CA125 and SR±SA+ROMA had a higher sensitivity (92%, 95% confidence interval [CI] 85-99% for both) than SR±SA (81%, 95% CI 71-91%), but SR±SA had a higher specificity (84%, 95% CI 77-91%). SR±SA+CA125 and SR±SA+ROMA improved diagnostic accuracy, each diagnosing 33.3% more malignant adnexal masses. Compared to SR±SA alone, SR±SA+CA125 showed a net reclassification improvement (NRI) of 28.8% at an extra cost of €13, while the extra cost for SR±SA+ROMA was €33, being the gain in terms of NRI superimposable with SR±SA+CA125. Conclusions In our study sample SR±SA seems to be the best strategy to triage adnexal masses. Among postmenopausal women, SR±SA+CA125 increased the NRI at a reasonable extra cost. Our data does not justify the use of HE4 and ROMA in the initial triage of adnexal masses.

Magnetic reconnection is a process that contributes significantly to plasma dynamics and energy transfer in a wide range of plasma and magnetic field regimes, including inertial confinement fusion experiments, stellar coronae, and compact, highly magnetized objects like neutron stars. Laboratory experiments in different regimes can help refine, expand, and test the applicability of theoretical models to describe reconnection. Laser-plasma experiments exploring magnetic reconnection at a moderate intensity (IL ∼1014 W cm-2) have been performed previously, where the Biermann battery effect self-generates magnetic fields and the field dynamics studied using proton radiography. At high laser intensities (ILλL2>1018 Wcm-2μm2), relativistic surface currents and the time-varying electric sheath fields generate the azimuthal magnetic fields. Numerical modeling of these intensities has shown the conditions that within the magnetic field region can reach the threshold where the magnetic energy can exceed the rest mass energy such that σcold = B2/(μ0nemec2) > 1 [A. E. Raymond et al., Phys. Rev. E 98, 043207 (2018)]. Presented here is the analysis of the proton radiography of a high-intensity (∼1018 W cm-2) laser driven magnetic reconnection geometry. The path integrated magnetic fields are recovered using a "field-reconstruction algorithm" to quantify the field strengths, geometry, and evolution.

Accretion processes play a crucial role in a wide variety of astrophysical systems. Of particular interest are magnetic cataclysmic variables, where, plasma flow is directed along the star’s magnetic field lines onto its poles. A stationary shock is formed, several hundred kilometres above the stellar surface; a distance far too small to be resolved with today’s telescopes. Here, we report the results of an analogous laboratory experiment which recreates this astrophysical system. The dynamics of the laboratory system are strongly influenced by the interplay of material, thermal, magnetic and radiative effects, allowing a steady shock to form at a constant distance from a stationary obstacle. Our results demonstrate that a significant amount of plasma is ejected in the lateral direction; a phenomenon that is under-estimated in typical magnetohydrodynamic simulations and often neglected in astrophysical models. This changes the properties of the post-shock region considerably and has important implications for many astrophysical studies.

We calculate the Thomson scattering cross section in a non-relativistic, magnetized, high density plasma -- in a regime where collective excitations can be described by magnetohydrodynamics. We show that, in addition to cyclotron resonances and an elastic peak, the cross section exhibits two pairs of peaks associated with slow and fast magnetosonic waves; by contrast, the cross section arising in pure hydrodynamics possesses just a single pair of Brillouin peaks. Both the position and the width of these magnetosonic-wave peaks depend on the ambient magnetic field and temperature, as well as transport and thermodynamic coefficients, and so can therefore serve as a diagnostic tool for plasma properties that are otherwise challenging to measure., Main paper: pp 1-8. Appendix: pp 8-10. 2 figures

This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625, 51 (2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability [Bingham and Cairns, Phys. Plasmas 7, 3089 (2000); Melrose, Rev. Mod. Plasma Phys. 1, 5 (2017)].

The properties of supersonic, compressible plasma turbulence determine the behavior of many terrestrial and astrophysical systems. In the interstellar medium and molecular clouds, compressible turbulence plays a vital role in star formation and the evolution of our galaxy. Observations of the density and velocity power spectra in the Orion B and Perseus molecular clouds show large deviations from those predicted for incompressible turbulence. Hydrodynamic simulations attribute this to the high Mach number in the interstellar medium (ISM), although the exact details of this dependence are not well understood. Here we investigate experimentally the statistical behavior of boundary-free supersonic turbulence created by the collision of two laser-driven high-velocity turbulent plasma jets. The Mach number dependence of the slopes of the density and velocity power spectra agree with astrophysical observations, and supports the notion that the turbulence transitions from being Kolmogorov-like at low Mach number to being more Burgers-like at higher Mach numbers., Supersonic turbulence is relevant to astrophysical plasmas with their study mostly limited to numerical simulations. Here the authors demonstrate supersonic turbulence in collisional high Mach number plasma jets generated in laboratory by using high power lasers.

Intense lasers interacting with dense targets accelerate relativistic electron beams, which transport part of the laser energy into the target depth. However, the overall laser-to-target energy coupling efficiency is impaired by the large divergence of the electron beam, intrinsic to the laser–plasma interaction. Here we demonstrate that an efficient guiding of MeV electrons with about 30 MA current in solid matter is obtained by imposing a laser-driven longitudinal magnetostatic field of 600 T. In the magnetized conditions the transported energy density and the peak background electron temperature at the 60-μm-thick target's rear surface rise by about a factor of five, as unfolded from benchmarked simulations. Such an improvement of energy-density flux through dense matter paves the ground for advances in laser-driven intense sources of energetic particles and radiation, driving matter to extreme temperatures, reaching states relevant for planetary or stellar science as yet inaccessible at the laboratory scale and achieving high-gain laser-driven thermonuclear fusion., Efficient energy transport by laser-driven relativistic electron beams is crucial in many applications including inertial confinement fusion, and particle acceleration. Here the authors demonstrate relativistic electron beam guiding in dense plasma with an externally imposed high magnetic field.

Magnetic fields are ubiquitous in the Universe. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter. The standard theoretical model for the origin of these strong magnetic fields is through the amplification of tiny seed fields via turbulent dynamo to the level consistent with current observations. However, experimental demonstration of the turbulent dynamo mechanism has remained elusive, since it requires plasma conditions that are extremely hard to re-create in terrestrial laboratories. Here we demonstrate, using laser-produced colliding plasma flows, that turbulence is indeed capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. These results support the notion that turbulent dynamo is a viable mechanism responsible for the observed present-day magnetization., Seventh Framework Programme (European Commission) (Grant 256973), Seventh Framework Programme (European Commission) (Grant 247039), United States. Department of Energy (Lawrence Livermore National Laboratory. Contract B591485), United States. Department of Energy (Grant DE-NA0003539)

With the advent of high power lasers, new opportunities have opened up for simulating astrophysical processes in the laboratory. We show that 2nd-order Fermi acceleration can be directly investigated at the National Ignition Facility, Livermore. This requires measuring the momentum-space diffusion of 3 MeV protons produced within a turbulent plasma generated by a laser. Treating Fermi acceleration as a biased diffusion process, we show analytically that a measurable broadening of the initial proton distribution is then expected for particles exiting the plasma., Comment: 7 pages, 6 figures; Added missing plasma parameters in Table 1, improved consideration of additional broadening

Objective Intraoperative specimen mammography (ISM) is a diffuse technique that allows surgeons to check specimens immediately after lumpectomy. Although the specimen is slightly compressed, the radiological image can be distorted by tissue overlap, and this may affect the evaluation of tumour borders, resulting in extension of the lumpectomy. As ISM may be less precise due to inadequate compression, a vacuum effect was applied to the specimen to increase the precision of margin detection. Study design This study was conducted at St. Anna Hospital Breast Unit, Turin, Italy. Women who underwent lumpectomy for cancer were eligible for inclusion. Both standard ISM (sISM) and vacuum ISM (vISM) were performed. Eighteen specimens obtained after lumpectomy from 1 April 2018 to 31 April 2018 were scanned. sISM (two orthogonal projections) was performed. Next, the specimen was placed in a vacuum, and vISM was performed. The examination was completed with a second orthogonal projection after removal of the vacuum, replacement of the specimen and repositioning of the vacuum. Additional tissue was removed if the surgeon considered that excision was inadequate. Finally, the specimen was sent for definitive histopathological analysis, which is the gold standard for the assessment of surgical margins. Intraoperative histological margin assessment was not performed. The sISM and vISM images and final histopathology reports were compared. Results For sISM, specificity was 47 % [95 % confidence interval (CI) 25–70], sensitivity was 67 % (95 % CI 21–94), positive predictive value (PPV) was 20 % (95 % CI 6–51) and negative predictive value (NPV) was 88 % (95 % CI 53–98). For vISM, specificity was 100 % (95 % CI 80–100), sensitivity was 67 % (95 % CI 21–94), PPV was 100 % (95 % CI 34–100) and NPV was 94 % (95 % CI 72–99). Conclusion These data suggest that the vacuum technique is feasible, cost-saving and yields results that are similar to those from frozen sections but without the limitations, such as prolonged operating time, high variability in sensitivity due to pathologists’ abilities, risk of compromising the histological report, and unreliability for small lumps and ductal carcinoma in situ.

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., Shock synthesis of diamond and even harder carbon polymorphs from graphite is of great interest for science and technology. Here, the authors present unprecedented in situ measurements of the structural changes, showing ultrafast formation of diamond and, at higher pressures, evidence for a pure lonsdaleite structure.

International audience; Many supernova remnants (SNRs), such as G296.5 + 10.0, exhibit an axisymmetric or barrel shape. Such morphologies have previously been linked to the direction of the Galactic magnetic field (GMF) although this remains uncertain. These SNRs generate magnetohydrodynamic (MHD) shocks in the interstellar medium (ISM), modifying its physical and chemical properties. The ability to study these shocks through observations is difficult due to the small spatial scales involved. In order to answer these questions, we perform a scaled laboratory experiment in which a laser-generated blast wave expands under the influence of a uniform magnetic field. The blast wave exhibits a spheroidal shape, whose major axis is aligned with the magnetic field, in addition to a more continuous shock front. The implications of our results are discussed in the context of astrophysical systems.

Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results show that the transport is diffusive and that, for the regime of interest for the highest-energy cosmic rays, the diffusion coefficient is unaffected by the spatial intermittency of the magnetic field., Comment: Updated Author and Reviewer Information, 23 pages 17 figures

We use an alternative interpretation of quantum mechanics, based on the Bohmian trajectory approach, and show that the quantum effects can be included in the classical equation of motion via a conformal transformation on the background metric. We apply this method to the Robertson-Walker metric to derive a modified version of Friedmann's equations for a Universe consisting of scalar, spin-zero, massive particles. These modified equations include additional terms that result from the non-local nature of matter and appear as an acceleration in the expansion of the Universe. We see that the same effect may also be present in the case of an inhomogeneous expansion., Accepted for publication in ApJ

Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for ${\geqslant}$kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This diagnostic has been implemented using the Thomson scattering probe beam and the resultant path-integrated magnetic field has been compared with that of proton radiography. Accurate measurement of magnetic fields is essential for satisfying the scientific goals of many current laser–plasma experiments.

We propose a mechanism for the generation of a magnetic field in the early universe during the QCD crossover assuming that dark matter is made of axions. Thermoelectric fields arise at pressure gradients in the primordial plasma due to the difference in charge, energy density and equation of state between the quark and lepton components. The axion field is coupled to the EM field, so when its spatial gradient is misaligned with the thermoelectric field, an electric current is driven. Due to the finite resistivity of the plasma an electric field appears that is generally rotational. For a QCD axion mass consistent with observational constraints and a conventional efficiency for turbulent dynamo amplification --- driven by the same pressure gradients responsible for the thermoelectric fields --- a magnetic field is generated on subhorizon scales. After significant Alfv\'enic unwinding it reaches a present day strength of $B \sim 10^{-13 }$ G on a characteristic scale $L_B \sim $ 20 pc. The resulting combination of $BL_B^{1/2}$ is significantly stronger than in any astrophysical scenario, providing a clear test for the cosmological origin of the field through $\gamma$-ray observations of distant blazars. The amplitude of the pressure gradients may be inferred from the detection of concomitant gravitational waves, while several experiments are underway to confirm or rule out the existence of axions., Comment: Published in PRL

We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.

International audience; We describe a setup for performing inelastic X-ray scattering and X-ray diffraction measurements at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light Source. This technique is capable of performing high-, meV-resolution measurements of dynamic ion features in both crystalline and non-crystalline materials. A four-bounce silicon (533) monochromator was used in conjunction with three silicon (533) diced crystal analyzers to provide an energy resolution of ∼50 meV over a range of ∼500 meV in single shot measurements. In addition to the instrument resolution function, we demonstrate the measurement of longitudinal acoustic phonon modes in polycrystalline diamond. Furthermore, this setup may be combined with the high intensity laser drivers available at MEC to create warm dense matter and subsequently measure ion acoustic modes.

Astrophysical shocks are commonly revealed by the non-thermal emission of energetic electrons accelerated in situ1–3. Strong shocks are expected to accelerate particles to very high energies4–6; however, they require a source of particles with velocities fast enough to permit multiple shock crossings. While the resulting diffusive shock acceleration 4 process can account for observations, the kinetic physics regulating the continuous injection of non-thermal particles is not well understood. Indeed, this injection problem is particularly acute for electrons, which rely on high-frequency plasma fluctuations to raise them above the thermal pool7,8. Here we show, using laboratory laser-produced shock experiments, that, in the presence of a strong magnetic field, significant electron pre-heating is achieved. We demonstrate that the key mechanism in producing these energetic electrons is through the generation of lower-hybrid turbulence via shock-reflected ions. Our experimental results are analogous to many astrophysical systems, including the interaction of a comet with the solar wind 9 , a setting where electron acceleration via lower-hybrid waves is possible. Electrons can be accelerated by astrophysical shocks if they are sufficiently fast to start with. As laboratory laser-produced shock experiments reveal, this can be achieved by lower-hybrid waves generated by a shock-reflected ion instability.

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense matter studies of micrometer-sized samples in laser-plasma experiments.

The physics of compressible turbulence in high energy density (HED) plasmas is an unchartered experimental area. Simulations of compressible and radiative flows relevant for astrophysics rely mainly on subscale parameters. Therefore, we plan to perform turbulent hydrodynamics experiments in HED plasmas (TurboHEDP) in order to improve our understanding of such important phenomena for interest in both communities: laser plasma physics and astrophysics. We will focus on the physics of supernovae remnants which are complex structures subject to fluid instabilities such as the Rayleigh–Taylor and Kelvin–Helmholtz instabilities. The advent of megajoule laser facilities, like the National Ignition Facility and the Laser Megajoule, creates novel opportunities in laboratory astrophysics, as it provides unique platforms to study turbulent mixing flows in HED plasmas. Indeed, the physics requires accelerating targets over larger distances and longer time periods than previously achieved. In a preparatory phase, scaling from experiments at lower laser energies is used to guarantee the performance of future MJ experiments. This subscale experiments allow us to develop experimental skills and numerical tools in this new field of research, and are stepping stones to achieve our objectives on larger laser facilities. We review first in this paper recent advances in high energy density experiments devoted to laboratory astrophysics. Then we describe the necessary steps forward to commission an experimental platform devoted to turbulent hydrodynamics on a megajoule laser facility. Recent novel experimental results acquired on LULI2000, as well as supporting radiative hydrodynamics simulations, are presented. Together with the development of LiF detectors as transformative X-ray diagnostics, these preliminary results are promising on the way to achieve micrometric spatial resolution in turbulent HED physics experiments in the near future.