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Resumo A cimeira de junho de 2021 correu muito bem. Foi marcante, porque pautou-se pelo «reencontro» desejado entre os dois lados do Atlântico. Foi ambiciosa, porque analisou planos detalhados para um novo Conceito Estratégico do próximo ano e para um caminho a ser traçado até 2030. Foi, ainda, e seguindo a tradição do passado, muito enriquecedora e clarificante, porque permitiu evidenciar velhas e novas questões que precisam de muito mais discussão, negociação e consenso, e a merecida presença de Portugal neste debate anunciado, face à sua reconhecida credibilidade e aos inestimáveis contributos que produz para uma Aliança mais forte e coesa.

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The Scattered Light Time-history Diagnostic (SLTD) is being implemented at the National Ignition Facility (NIF) to greatly expand the angular coverage of absolute scattered-light measurements for direct- and indirect-drive inertial confinement fusion (ICF) experiments. The SLTD array will ultimately consist of 15 units mounted at a variety of polar and azimuthal angles on the NIF target chamber, complementing the existing NIF backscatter suite. Each SLTD unit collects and diffuses scattered light onto a set of three optical fibers, which transport the light to filtered photodiodes to measure scattered light in different wavelength bands: stimulated Brillouin scattering (350 nm–352 nm), stimulated Raman scattering (430 nm–760 nm), and ω/2 (695 nm–745 nm). SLTD measures scattered light with a time resolution of ∼1 ns and a signal-to-noise ratio of up to 500. Currently, six units are operational and recording data. Measurements of the angular dependence of scattered light will strongly constrain models of laser energy coupling in ICF experiments and allow for a more robust inference of the total laser energy coupled to implosions.

Laser-plasma accelerators (LPAs) driven by picosecond-scale, kilojoule-class lasers can generate particle beams and x-ray sources that could be utilized in experiments driven by multi-kilojoule, high-energy-density science (HEDS) drivers such as the OMEGA laser at the Laboratory for Laser Energetics (LLE) or the National Ignition Facility at Lawrence Livermore National Laboratory. This paper reports on the development of the first LPA driven by a short-pulse, kilojoule-class laser (OMEGA EP) connected to a multi-kilojoule HEDS driver (OMEGA). In experiments, electron beams were produced with electron energies greater than 200 MeV, divergences as low as 32 mrad, charge greater than 700 nC, and conversion efficiencies from laser energy to electron energy up to 11%. The electron beam charge scales with both the normalized vector potential and plasma density. These electron beams show promise as a method to generate MeV-class radiography sources and improved-flux broadband x-ray sources at HEDS drivers.

The generation of hot, directional electrons via laser-driven stimulated Raman scattering (SRS) is a topic of great importance in inertial confinement fusion (ICF) schemes. Little recent research has been dedicated to this process at high laser intensity, in which back, side, and forward scatter simultaneously occur in high energy density plasmas, of relevance to, for example, shock ignition ICF. We present an experimental and particle-in-cell (PIC) investigation of hot electron production from SRS in the forward and near-forward directions from a single speckle laser of wavelength ${\ensuremath{\lambda}}_{0}=1.053\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$, peak laser intensities in the range ${I}_{0}=0.2--1.0\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{4pt}{0ex}}{\mathrm{Wcm}}^{\ensuremath{-}2}$ and target electron densities between ${n}_{e}=0.3--1.6%\phantom{\rule{0.28em}{0ex}}{n}_{c}$, where ${n}_{c}$ is the plasma critical density. As the intensity and density are increased, the hot electron spectrum changes from a sharp cutoff to an extended spectrum with a slope temperature $T=34\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ and maximum measured energy of 350 keV experimentally. Multidimensional PIC simulations indicate that the high energy electrons are primarily generated from SRS-driven electron plasma wave phase fronts with k vectors angled $\ensuremath{\sim}{50}^{\ensuremath{\circ}}$ with respect to the laser axis. These results are consistent with analytical arguments that the spatial gain is maximized at an angle which balances the tendency for the growth rate to be larger for larger scattered light wave angles until the kinetic damping of the plasma wave becomes important. The efficiency of generated high energy electrons drops significantly with a reduction in either laser intensity or target electron density, which is a result of the rapid drop in growth rate of Raman scattering at angles in the forward direction.

Slow and fast light require precise tailoring of the refractive index of a medium. We present the first experimental demonstration of such control inside plasma, reporting group velocity of light between 0.12c and -0.34c.

Self-induced plasma gratings are now routinely used in inertial confinement fusion experiments at the National Ignition Facility (NIF) to achieve precise spatio-temporal control of the laser energy deposition directly inside the fusion targets. This novel capability is enabled by applying a few Å wavelength shifts between different groups of beams, in order to control the direction and level of light scattering off these plasma gratings. A new wavelength tuning capability was added on the NIF in January 2020 to extend the range of applications of plasma gratings; such applications include the control of several asymmetry modes during the implosion, and mitigation of backscatter from stimulated Raman or Brillouin scattering.

Interference between crossed femtosecond lasers can drive spatially varying ionization, producing a high-flux plasma optic. We measure the plasma and optical properties of an ionization grating in air as it redirects a millijoule-scale probe beam.

Slow and fast light, or large changes in the group velocity of light, have been observed in a range of optical media, but the fine optical control necessary to induce an observable effect has not been achieved in a plasma. Here, we describe how the ion-acoustic response in a fully ionized plasma can produce large and measurable changes in the group velocity of light. We show the first experimental demonstration of slow and fast light in a plasma, measuring group velocities between 0.12c and -0.34c.

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Como têm respondido as Forças Armadas à emergência COVID-19? Que impactos tem esta crise na organização e nas missões militares? Em que medida afetará os recursos que lhes são alocados, ou o peso relativo de diferentes serviços ou áreas internamente? Que lições para a articulação com outras forças de segurança e organizações civis? Estas são algumas das questões que colocámos aos especialistas convidados neste IDN Brief. Para além de participantes nacionais desafiámos também analistas de França, Reino Unido, Holanda, Canadá e África do Sul que nos trazem reflexões a partir da experiência dos seus países. Os desafios que enfrentamos exigem cada vez mais partilha de informação, aprendizagem cruzada e respostas cooperativas. info:eu-repo/semantics/publishedVersion

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

This work discusses the development of x-ray and gamma-ray sources based on laser-wakefield acceleration (LWFA) in the self-modulated regime. These sources are developed for probing high energy density (HED) science experiments at large-scale laser facilities.

This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 um (Omega EP) and 10 um (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy 50 MeV protons (energy spread of, 16 pages, 7 figures

Religions have always been, and still are, an exploited, manipulated, exacerbated and wrongly interpreted factor. Nonetheless, they are, most of the times, central to understanding the causes and explanations of many of the past, ongoing and future wars and conflicts. I will try to frame the importance of this factor in history, in accordance with each geopolitical circumstance, and inasmuch as it is understood, is differentiated and is applied both in society as in the political choices of every state. Finally, I will try to analyze the importance of the public institutions, in particular the Armed Forces, in managing violence and ensuring peace., O religioso sempre foi e é um fator explorado, manipulado, exacerbado, mal interpretado, mas, muitas das vezes, central nas causas e explicações de muita da conflitualidade e das guerras, passadas, atuais e futuras. Neste texto, procuraremos enquadrar a importância deste fator na história, de acordo com a circunstância geopolítica, na forma como se entende, diferencia e aplica, tanto na sociedade como nas escolhas políticas de cada Estado. Por último, tentaremos analisar a importância do papel das instituições públicas, e em especial dos exércitos, na gestão da violência e na garantia da paz.

Experiments and simulations have been conducted to investigate the efficacy of Ta2O5-lined Hohlraum walls at reducing stimulated Brillouin backscattering (SBS) as well as any subsequent effects on the Hohlraum dynamics and capsule implosions in indirect drive experiments at the National Ignition Facility. Using a 1.1 MJ 400 TW, 351 nm, shaped laser pulse, we measure a 5× reduction in SBS power in the peak of the pulse from the wall on the outer 50° cone beams. The SBS spectrum indicates a reduction in the high-Z spectral signature when using multispecies wall materials. Detailed hydrodynamic simulations were performed using different heat conduction models with flux limiters. Additional simulations were performed on the plasma maps using the 3D parallel paraxial code pF3D to compare backscatter powers between the pure Au and Ta2O5-lined Hohlraums. Further analysis, using hydrodynamically equivalent plasmas, shows that the SBS reduction is clearly a result of the added ion Landau damping caused by the oxygen ions and not from differences in plasma conditions. The experimental and simulation results also show an increase in the wall plasma expansion when using the Ta2O5 liner leading to a 70% more oblate implosion.

New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic (∼1018 W/cm2) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large ∼100 μm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux ∼ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.

Raman side scatter, whereby scattered light is resonant while propagating perpendicularly to a density gradient in a plasma, was identified experimentally in planar-target experiments at the National Ignition Facility at intensities orders of magnitudes below the threshold for absolute instability. We have derived a new theoretical description of convective Raman side scatter below the absolute threshold, validated by numerical simulations. We show that inertial confinement fusion experiments at full ignition scale, i.e., with mm-scale spot sizes and density scale lengths, are prone to increased coupling losses from Raman side scatter as the instability can extend from the absolute regime near the quarter-critical density to the convective regime at lower electron densities.

Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefield acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.

The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 – 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process.

A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps–20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

Cross beam energy transfer (CBET), invoked by setting a wavelength difference, Δλ, between inner and outer beam cones, can be used to increase the drive on the waist in indirectly driven inertial confinement fusion experiments at the National Ignition Facility (NIF). Historically, hot spot symmetry control in capsule implosions in high (≥0.9 mg/cm3 4He) gas fill Hohlraums was enabled by substantial CBET. However, these implosion designs suffered from inflight symmetry swings, high SRS backscatter on the inner cones, and significant hot electron generation posing a threat to DT fuel preheat. Subsequent experiments in larger, low (≤0.6 mg/cm3 4He) gas fill Hohlraums demonstrated round implosions by varying the inner cone fraction throughout the laser drive at Δλ = 0 A while keeping backscatter and hot electron generation very low. To enable driving larger capsules at a given Hohlraum size, additional tools for implosion symmetry control are required. With this goal in mind, this paper presents a detailed experimental study of using CBET in low gas fill Hohlraums near NIF's current peak power capability. We find a ∼2.5× higher sensitivity of the P2 Legendre mode with respect to Δλ changes compared to that of high gas fill designs. We attribute this observation to the fact that backscatter remains very low and that CBET remains in a linear regime, as suggested by simulations. As a result, a much smaller Δλ of order 1 A is sufficient for sustaining implosion symmetry while keeping laser-to-Hohlraum coupling high and hot electron generation very low. While this study used plastic ablator capsules, our findings can be generalized to other ablator materials and, hence, show great promise for using wavelength detuning as a strong lever for implosion symmetry control in future low gas fill designs that require smaller case to capsule ratios in order to increase the energy coupled to the capsule.

Recent experiments systematically studied subscale beryllium-capsule implosions on NIF [A.B. Zylstra et al., Phys. Plasmas 26, 052707 (2019)], finding that the performance was well explained by invoking an inline model for mix at the fuel ablator interface. This model is optimistic about the performance of full-scale beryllium implosions, motivating an exploratory study on tactics for fielding larger capsules within the current limits of power and energy available at NIF. Here we report the results of that work, finding that using a ‘picketless’ pulse would allow a 25% increase in capsule size, which is predicted to substantially improve performance.

Large quantities of ultrahigh-energy x-rays are produced by petawatt-class lasers; however, spectroscopy in this range of 0.1-1 MeV is difficult due to the long photon mean free path. A novel geometry step filter to measure the high-energy bremsstrahlung emission tail has been developed for use in high energy density, short-pulse laser-matter interaction experiments. The grid design of the filters allows for the independent determination of a local background, which reduces systematic errors in the reconstructed spectra. This spectrometer was used to measure x-ray spectra for various laser and target conditions at intensities near 1 × 1018 W/cm2 where single-exponential bremsstrahlung spectra were fit to the data and show an increasing photon temperature with pulse duration for a fixed laser intensity.

Experiments using the Advanced Radiographic Capability (ARC) laser at the National Ignition Facility (NIF) aim to characterize short-pulse-driven proton beams for use as both probes and drivers for high-energy-density physics experiments. Measurements of ARC-driven proton beam characteristics, such as energy spectrum and conversion efficiency, rely on the NIF Electron Positron Proton Spectrometer (NEPPS). The NEPPS diagnostic is a version of an existing particle spectrometer which is used for detecting MeV electron and positron spectra via permanent magnetic field dispersion. These spectrometers have not yet been calibrated for protons and instead use an analytical calculation to estimate the dispersion. Small variations in the field uniformity can affect the proton dispersion due to the relatively small resolving power (E/dE) for this diagnostic. A broadband energy, laser-accelerated proton source was produced at the Titan laser to experimentally calibrate the proton dispersion. These experimental data were used to test the theoretical dispersion. Numerical simulations using measurements of the magnetic field variation within the diagnostic were used to obtain a realistic proton dispersion curve for the new NEPPS units. This procedure for obtaining each independent dispersion is applicable to all EPPS and NEPPS diagnostics, given the axial magnetic field profile.

Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $\mu$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions., Comment: Accepted for publication in Physical Review Accelerators and Beams

This paper presents a summary of the presentations and discussions of Working Group 7 (WG7): Radiation and Advanced Concepts. This working group was part of the 2018 Advanced Accelerator Concepts Workshop held at Breckenridge, Colorado, from August 12 to 17, 2018. There was wide-range of topics covered by this working group raging from electromagnetic radiation generated by beams (both as a diagnostic and as a source) and advanced concepts that fall outside the scope of the other working groups.

We experimentally demonstrate that plasma waveguides produced with ultra-short laser pulses (sub-picosecond) in gas jets are capable of guiding high intensity laser pulses. This scheme has the unique ability of guiding a high-intensity laser pulse in a plasma waveguide created by the same laser system in the very simple and stable experimental setup. A hot plasma column was created by a femtosecond class laser that expands into an on-axis parabolic low density profile suitable to act as a waveguide for high intensity laser beams. We have successfully guided ~1015 W cm−2 laser pulses in a 8 mm long hydrogen plasma waveguide with a 35% guiding efficiency.

The increasing demand for high laser powers is placing huge demands on current laser technology. This is now reaching a limit, and to realise the existing new areas of research promised at high intensities, new cost-effective and technically feasible ways of scaling up the laser power will be required. Plasma-based laser amplifiers may represent the required breakthrough to reach powers of tens of petawatt to exawatt, because of the fundamental advantage that amplification and compression can be realised simultaneously in a plasma medium, which is also robust and resistant to damage, unlike conventional amplifying media. Raman amplification is a promising method, where a long pump pulse transfers energy to a lower frequency, short duration counter-propagating seed pulse through resonant excitation of a plasma wave that creates a transient plasma echelon that backscatters the pump into the probe. Here we present the results of an experimental campaign conducted at the Central Laser Facility. Pump pulses with energies up to 100 J have been used to amplify sub-nanojoule seed pulses to near-joule level. An unprecedented gain of eight orders of magnitude, with a gain coefficient of 180 cm−1 has been measured, which exceeds high-power solid-state amplifying media by orders of magnitude. High gain leads to strong competing amplification from noise, which reaches similar levels to the amplified seed. The observation of 640 Jsr−1 directly backscattered from noise, implies potential overall efficiencies greater than 10%.

We investigate a new regime for betatron x-ray emission that utilizes kilojoule-class picosecond lasers to drive wakes in plasmas. When such laser pulses with intensities of ∼5×10^{18} W/cm^{2} are focused into plasmas with electron densities of ∼1×10^{19} cm^{-3}, they undergo self-modulation and channeling, which accelerates electrons up to 200 MeV energies and causes those electrons to emit x rays. The measured x-ray spectra are fit with a synchrotron spectrum with a critical energy of 10-20 keV, and 2D particle-in-cell simulations were used to model the acceleration and radiation of the electrons in our experimental conditions.

O que é o Inimigo? Apesar do facto de as organizações envolvidas no extremismo e na violência serem bem conhecidas, tal como as justificações ideológicas relativas às ações que realizam, muito menos entendida pela maioria dos observadores são os fundamentos individuais dos membros que as apoiam e executam. A suposição convencional comum assenta no argumento de que o comportamento extremista está enraizado em doutrinas derivadas do corpus islâmico e da sua suposta propensão para a violência. Esta análise procura demonstrar que uma explicação mais abrangente e satisfatória pode estar relacionada com fatores históricos, sociais e psicológicos e que, além disso, a atual onda de “terrorismo islâmico” difere pouco das ondas precedentes de violência extremista que enfrentaram e tentaram substituir o Estado. Teorizando a Violência Performativa: Islamismo Radical e Decapitações em Perspetiva O ensaio explora uma das mais decisivas e profundas variantes da violência corporal – a decapitação. Em tempos, comum a todas as culturas, esta forma de punição desapareceu na maioria das sociedades modernas. No entanto, existem algumas sociedades que incentivam a decapitação por motivos religiosos ou culturais. O estu- do procura examinar e compreender os propósitos autóctones e os significados culturais do ritual da decapitação. A preocupação central é: porquê decapitar? Muitas vezes é difícil e quase impossível obter uma resposta direta da cultura ou do indivíduo que é o coração deste acto sangrento. Propõe-se uma linha argumentativa que problematiza a decapitação no contexto contemporâneo. Concomitantemente, examinam-se várias perspetivas teóricas e filosóficas que ajudam a enquadrar este fenómeno. De acordo com a avaliação empírica, confinamos a discussão a dois casos contemporâneos bem conhecidos: os casos esporádicos de decapitação por parte dos talibãs no Afeganistão e os métodos de execução pública conduzidos pelos militantes do (autodenominado) Estado Islâmico (EI). Este artigo tem dois objetivos principais. Primeiro, apresentar os movimentos jiadistas em quatro grandes grupos: a Al-Qaeda, o Daesh, os independentes e os híbridos. Segundo, diferenciar a ação dos grupos em jiadismo violento e não violento. A análise junta a geopolítica, o caráter interno dos Estados, a transnacionalidade do fenómeno e a multiplicidade de critérios de classificação, segun- do as três dimensões propostas: ideologias, estratégias e objetivos. Jihadismo no Sahel: a Expansão da Ameaça Obscura O Sahel é uma região extraordinariamente complexa na qual as organizações extremistas coexistem e interagem em diferentes graus com organizações criminosas, milícias étnicas, grupos armados e autoridades governamentais, criando um ambiente de insegurança que dificulta a ação do controlo dos governos sobre o seu território, ao mesmo tempo que facilita a expansão da mensagem jihadista e da insurgência armada. Um elemento-chave na avaliação do futuro cenário de segurança na região é dado pela situação na Líbia, um país que parecia destinado a tornar-se uma base de retaguarda e apoio aos grupos que combatiam na Síria e no Iraque, bem como um novo território de jihad para o Daesh no norte de África. A conquista de Sirte em dezembro de 2016 abre a possibilidade de que os restantes grupos jihadistas vencidos, juntamente com os combatentes que conseguirem sobreviver aos combates na Síria e no Iraque, se mudem para o Sahel tornando-se este no teatro principal para as operações jihadistas internacionais. As presentes circunstâncias tornam necessário examinar a evolução dos grupos extremistas no Sahel e o complicado jogo político, económico e militar em que estão atualmente envolvidos, para que possamos identificar as suas estratégias, analisar a sua resiliência e avaliar as suas possibilidades de sobrevivência à ação concertada dos governos regionais e da comunidade internacional, empenhados em evitar que o centro de gravidade da ação jihadista se mova para esta região complexa. Processos de Radicalização no Sahel e a Evolução dos Movimentos de Militantes Islamistas no Mali (2012-2018) O artigo situa a trajetória dos vários movimentos islamistas no Mali desde a crise de 2012. O argumento central desafia as explicações monocausais do terrorismo que apresentam a religião, e em particular o Islão, como a sua principal causa. Em contraste, o artigo analisa o contexto local para identificar as múltiplas clivagens que permeiam a sociedade do Mali. O enquadramento histórico permanece essencial para entender as tensões e rivalidades nas várias interpretações do Islão no Mali entre os denominados moderados/tradicionalistas, reformistas e os jihadistas salafi. Uma análise das rivalidades intra-étnicas, bem como inter-étnicas em relação com a economia política da região do Sahara-Sahel é central para compreender o padrão volátil de formação de alianças, bem como os padrões de amizade e inimizade que se afiguram como inesperados à partida. Finalmente, tanto as respostas do Estado, como dos atores regionais e externos reconfiguraram a paisagem política e religiosa. O processo em curso de constituição de ordens políticas divergentes continua a desafiar o Estado e influencia a perpetuação do extremismo violento na região. Este artigo analisa o impacto e evolução da ameaça jihadista takfiri no Médio Oriente e Magrebe, tendo em conta a perda pelo autoproclamado Califado do Daesh do seu proto-estado territorial. Tendo em conta as dinâmicas observadas, argumenta-se que apesar da estratégia de territorialização desenvolvida pelo Daesh ter falhado, em resultado da derrota militar sofrida nos territórios do Iraque e da Síria, persistem fatores que explicam a resiliência do movimento, designadamente: a fragilidade dos Estados na sua eficácia e legitimidade; a existência de “vazios de poder” decorrentes de ambientes de conflitualidade; e a marginalização de setores das comunidades muçulmanas, em particular os mais jovens. Perante uma derrota territorial, o Daesh parece procurar evoluir na estrutura organizacional e estratégia operacional, reorientando-se para uma ação violenta descentralizada em detrimento do controlo de território. Esta transformação poderá resultar num agravamento da competição entre grupos de matriz jihadista takfiri e até originar novos movimentos, em resultado de cisões, ou a reorganização dos já existentes, sem que isso signifique necessariamente o desaparecimento desta ameaça violenta. info:eu-repo/semantics/publishedVersion

Characterizing the angular momentum carried by photons provides a new method of understanding the nature of laser-plasma interactions, beam-plasma interactions or beam propagation in an undulator. The recent results from experiments and simulations have shown that a plasma accelerator may be a promising source of ultrashort x-ray pulses with orbital angular momentum. However, the broadband and ultrashort nature of such a pulse makes it very challenging to measure the angular momentum properties of the photons. In this study, we review and discuss several potential methods for measurement of the orbital angular momentum from laser plasma accelerators.

Laser-plasma-based accelerators are now able to provide the scientific community with novel high-energy light sources that are essential to study high-energy density matter, inertial confinement fusion, astrophysical systems, and fundamental plasma physics. Due to the transient and high-density properties of these systems, it is essential to develop light sources that are in the hard x-ray energy range (0.01–1 MeV) and directional and have high yield, low divergence, and short duration (ps and sub-ps). In this work, we show that by using a Laser plasma accelerator, it is possible to generate a broadband (0.01–1 MeV) hard x-ray source that satisfies the previous requirements. A series of experiments were conducted on the Titan laser at the Lawrence Livermore National Laboratory where a 10 nC electron beam in the 10–380 MeV energy range was generated through a laser plasma accelerator. The electrons generate x-rays via their betatron motion (few-30 keV) and hard x-rays through inverse Compton scattering (10–250 keV) and/or Bremsstrahlung (up to 1 MeV). Due to its unique characteristics, this source can be an important tool for many applications in large-scale international laser facilities.

The high implosion velocity, high adiabat BigFoot design [Casey et al., Phys. Plasmas 25, 056308 (2018)] has produced the highest neutron yield to date in an ignition hohlraum on the National Ignition Facility. It has used up to 500 TW of peak power and nearly 2 MJ of laser energy in pulses up to 8 ns in duration, with the goal of fielding controlled implosions with high coupled energy, which can suppress deleterious hydrodynamic instabilities. However, when the laser pulse exceeds 6 ns with the laser energy greater than 1.6 MJ, stimulated Brillouin scattering (SBS) reaches levels that may damage optical components in the laser. Pending development of techniques to reduce SBS, limitation of laser power, and energy to avoid damage prevents the full exploitation of this approach to ignition. In this manuscript, we present three-dimensional simulations that match the experimentally measured SBS energy, in particular, reproducing quantitatively the time in the pulse when maximum backscatter occurs, and its magnitude across ∼10 BigFoot experiments. The demonstrated robustness of the modeling, which combines LASNEX and pF3D simulations, motivates us to explore and recommend several feasible SBS mitigation strategies: modified laser pointing, different laser frequencies for each cone of beams, increased laser bandwidth on all or some of the cones, and materials with a mixture of light and heavy atoms lining the inside of the hohlraum walls.