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Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology limitations. Here, we investigate how to optimize their coupling with solid targets. Experimentally, we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target backside. The underlying mechanisms are analyzed through multidimensional particle-in-cell simulations, revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection, which is one possible mechanism to boost electron energization. In addition, the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their collimation. Our simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.

Progress in laser-driven proton acceleration requires increasing the proton maximum energy and laser-to-proton conversion efficiency while reducing the divergence of the proton beam. However, achieving all these qualities simultaneously has proven challenging experimentally, with the increase in beam energy often coming at the cost of beam quality. Numerical simulations suggest that coupling multi-PW laser pulses with ultrathin foils could offer a route for such simultaneous improvement. Yet, experimental investigations have been limited by the scarcity of such lasers and the need for very stringent temporal contrast conditions to prevent premature target expansion before the pulse maximum. Here, combining the newly commissioned Apollon laser facility that delivers high-power ultrashort (∼24fs) pulses with a double plasma mirror scheme to enhance its temporal contrast, we demonstrate the generation of up to 35 MeV protons with only 5 J of laser energy. This approach also achieves improved laser-to-proton energy conversion efficiency, reduced beam divergence, and optimized spatial beam profile. Therefore, despite the laser energy losses induced by the plasma mirror, the proton beams produced by this method are enhanced on all accounts compared to those obtained under standard conditions. Particle-in-cell simulations reveal that this improvement mainly results from a better space–time synchronization of the maximum of the accelerating charge-separation field with the proton bunch.

Abstract Contemporary ultraintense, short-pulse laser systems provide extremely compact setups for the production of high-flux neutron beams, such as those required for nondestructive probing of dense matter, research on neutron-induced damage in fusion devices or laboratory astrophysics studies. Here, by coupling particle-in-cell and Monte Carlo numerical simulations, we examine possible strategies to optimise neutron sources from ion-induced nuclear reactions using 1-PW, 20-fs-class laser systems. To improve the ion acceleration, the laser-irradiated targets are chosen to be ultrathin solid foils, either standing alone or preceded by a plasma layer of near-critical density to enhance the laser focusing. We compare the performance of these single- and double-layer targets, and determine their optimum parameters in terms of energy and angular spectra of the accelerated ions. These are then sent into a converter to generate neutrons via nuclear reactions on beryllium and lead nuclei. Overall, we identify configurations that result in neutron yields as high as $$\sim 10^{10}\,{\mathrm{n}}\,{\mathrm{sr}}^{-1}$$ ∼ 10 10 n sr - 1 in $$\sim 1$$ ∼ 1 -cm-thick converters or instantaneous neutron fluxes above $$10^{23}\,{\mathrm{n}}\,{\mathrm{cm}}^{-2}\,{\mathrm{s}}^{-1}$$ 10 23 n cm - 2 s - 1 at the backside of $$\lesssim 100$$ ≲ 100 - $$\upmu$$ μ m-thick converters. Considering a realistic repetition rate of one laser shot per minute, the corresponding time-averaged neutron yields are predicted to reach values ( $$\gtrsim 10^7\,{\mathrm{n}} \,{\mathrm{sr}}^{-1}\,{\mathrm{s}}^{-1}$$ ≳ 10 7 n sr - 1 s - 1 ) well above the current experimental record, and this even with a mere thin foil as a primary target. A further increase in the time-averaged yield up to above $$10^8\,{\mathrm{sr}}^{-1}\,{\mathrm{s}}^{-1}$$ 10 8 sr - 1 s - 1 is foreseen using double-layer targets.

Magnetic reconnection acts as energy transfer process in plasma and induces processes like plasma heating, particle acceleration. Here the authors demonstrate the variation of magnetic reconnection between two flux tubes in the presence of external magnetic field.

Depuis 1970, les Jeux d’hiver de l’Arctique (JHA) rassemblent des jeunes du monde circumpolaire. Rencontre sportive et culturelle, ils valorisent le partage et l’échange entre jeunes de même que les pratiques culturelles et sportives autochtones (jeux Dene, sports arctiques). Ils entendent ainsi participer à bâtir une communauté arctique. Cet article propose une réflexion sur cet évènement et montre que ce type de rencontre, au-delà de son aspect sportif, peut constituer un levier de développement social, culturel, éducatif pour un territoire. Partant, ce texte consiste en une interrogation du mouvement sportif contemporain. En questionnant la valeur publique des JHA, il discute du paradigme sur lesquels les évènements sportifs internationaux sont aujourd’hui construits.

Abstract We analyze, using experiments and 3D MHD numerical simulations, the dynamic and radiative properties of a plasma ablated by a laser (1 ns, 10 $$^{12}$$ 12 –10 $$^{13}$$ 13 W/cm $$^2$$ 2 ) from a solid target as it expands into a homogeneous, strong magnetic field (up to 30 T) that is transverse to its main expansion axis. We find that as early as 2 ns after the start of the expansion, the plasma becomes constrained by the magnetic field. As the magnetic field strength is increased, more plasma is confined close to the target and is heated by magnetic compression. We also observe that after $$\sim 8$$ ∼ 8 ns, the plasma is being overall shaped in a slab, with the plasma being compressed perpendicularly to the magnetic field, and being extended along the magnetic field direction. This dense slab rapidly expands into vacuum; however, it contains only $$\sim 2\%$$ ∼ 2 % of the total plasma. As a result of the higher density and increased heating of the plasma confined against the laser-irradiated solid target, there is a net enhancement of the total X-ray emissivity induced by the magnetization.

Magnetized laser-produced plasmas are central to many studies in laboratory astrophysics, in inertial confinement fusion, and in industrial applications. Here, we present the results of large-scale three-dimensional magnetohydrodynamic simulations of the dynamics of a laser-produced plasma expanding into a transverse magnetic field with a strength of tens of teslas. The simulations show the plasma being confined by the strong magnetic field into a slender slab structured by the magnetized Rayleigh–Taylor instability that develops at the plasma–vacuum interface. We find that when the initial velocity of the plume is perturbed, the slab can develop kink-like motions that disrupt its propagation.

The design of ellipsoidal plasma mirrors (EPMs) for the PEARL laser facility is presented. The EPMs achieve a magnification of 0.32 in focal spot size, and the corresponding increase in focused intensity is expected to be about 8. Designing and implementing such focusing optics for short-pulse (

Hunting, fishing and gathering represent a particular part in the total range of variation among physical practices. Although these activities were not originally considered as sports, practitioners now consider them as such. In all cases, sport appears as a standard to – or against which – practitioners refer to. The way they understand their activities has thus expanded. Our purpose is to pinpoint how and why sport is now generally mentioned to qualify these activities either to compare (quite often) or contrast in terms of equipment, places and time. We show that sport characteristics don’t mean the same for those who practice and for the structures in charge of these activities. Referring to sport is both a result and a process aiming at giving value to places, equipment, activities, people, behaviours in order to enhance or denounce their image. We have combined data from written documents, participative observations and interviews with practitioners (n=68) to show that what characterizes hunting, fishing and gathering adapt to today social, cultural and legal conditions. Participants now turn toward a reference to sport in order to show a decent side of their activity.

During the annexation of Alsace by Germany between 1871 and 1914, the Vosges mountain range took on particular significance for the inhabitants of the region. It represented a boundary that both allowed the Alsatian people to assert their cultural distinctiveness, while at the same time ‘integrating’ Alsace into France, thereby symbolically preserving the region from attempts to assimilate it into the Reich. The way in which local mountain associations promoting hiking and skiing considered this political and cultural border reveals their unique perception of a natural boundary that was fixed by definition, but mobile in its representations. As we will see, these associations tended to particularly promote the existence of a cultural border area – real and imagined – that effectively set the Alsace region apart from both France and Germany. Within this context, the images of the ‘blue line of the Vosges’ held by the Alsatian members of these clubs differed greatly. Some considered it to be a unifying border that perpetuated the myth of the lost provinces, ritualised the crossing of the Franco-German border, and symbolised their strong ties with the French Alpine Club. Others saw the Vosges more as a dividing border, placing emphasis on language specificities and differences in cultural heritage, the use of mountain huts as centres to celebrate local traditions, and the integration of the mountain range within the ‘regional heritage’. In this sense, the main issue here was not so much the mobility of the political borders (from the Rhine to the Vosges during the German annexation of Alsace), but rather the shifts in the very meaning attributed to this border area.

Entre 1871 et 1914, la chaîne des Vosges constitue pour les Alsaciens, dont le territoire est alors annexé à l’Allemagne, une limite à la fois distinctive, dans la mesure où elle permet aux populations de revendiquer une singularité culturelle, et intégrative, parce qu’elle est aussi ce qui lie l’Alsace à la France et préserve donc la région d’un point de vue symbolique face aux tentatives d’assimilation au Reich. La manière dont les associations de montagne locales, qui promeuvent la randonnée pédestre et le ski, appréhendent cette frontière à la fois politique et culturelle permet de révéler leur perception singulière d’une limite naturelle fixe par définition, mais mobile dans ses représentations. Nous montrerons notamment que ces structures cultivent singulièrement l’existence d’une zone-frontière culturelle réelle et fantasmée, qui distingue l’Alsace à la fois de l’Allemagne et de la France. Dans ce cadre, l’image de la « ligne bleue des Vosges » est mobilisée, par les pratiquants alsaciens, comme une frontière tantôt unificatrice (perpétuation du mythe des provinces perdues, ritualisation du passage de la frontière franco-allemande, relations suivies avec le Club alpin français), tantôt séparatrice (mise en exergue des spécificités linguistiques et patrimoniales, utilisation du refuge comme lieu d’expression des traditions locales, intégration des Vosges à l’« héritage régional »). En ce sens, la question de la mobilité des frontières politiques (du Rhin vers les Vosges au cours de l’Annexion) s’efface clairement ici derrière une interrogation sur la mobilité du sens de la frontière vosgienne.

Lors de la session 1987 de la Conférence des ministres de la Jeunesse et des Sports de la Francophonie (CONFEJES) au Québec, la création d’une commission des sports de l’océan Indien est actée. Celle-ci s’ouvre, à partir de 1992, au secteur de la jeunesse en devenant la Commission de la Jeunesse et des Sports de l’océan Indien (CJSOI) dont l’objectif est de structurer des actions de coopération régionale (promotion des sports, opérations culturelles, échanges et actions de formation de cadres, etc.) pour encourager les jeunes de cette aire géographique à se rencontrer, à mieux se connaître et à s’exprimer et par le biais du sport et de la culture. Dans ce cadre, elle met sur pied les Jeux de la CJSOI. Si les Jeux des îles de l’océan Indien sont relativement bien connus et ont fait l’objet de divers travaux scientifiques, leurs homologues pour la jeunesse restent plutôt dans leur ombre. Organisés pour la première fois par l’île Maurice en 1995, ils ont lieu tous les deux ans. Ils rassemblent, selon les éditions, entre 500 et 1 000 jeunes de 14 à 18 ans représentant l’union des Comores, la république de Madagascar, la république de Maurice, la république des Seychelles, La Réunion ainsi que, depuis 2003, la république de Djibouti, et, depuis 2005, Mayotte. Bâtis sur le principe d’une complémentarité entre activités sportives et culturelles et de l’échange entre jeunes, ils font de la francophonie un pilier. Cet article se base sur une recherche documentaire et une observation ethnographique réalisée lors des Jeux de 2016 à Madagascar. Il ressort de ce travail sur l’expérience vécue des participants lors de l’évènement ainsi que sur les fondements idéologiques et organisationnels de celui-ci, que la francophonie peut permettre de tisser des liens au sein de cet espace régional traversé de tensions politiques, sociales et économiques. Inévitablement marqués par un contexte géopolitique local problématique, ces Jeux promeuvent pour autant la fraternité par les échanges linguistiques et culturels que permettent les activités socio-éducatives et les sports. Ils constituent aujourd’hui l’une des actions les plus importantes de la CJSOI, du fait de leur potentiel de promotion de l’amitié et de la fraternité entre jeunes de l’océan Indien.

We show efficient laser driven proton acceleration up to 14 MeV from a 62 μm thick cryogenic hydrogen ribbon. Pulses of the short pulse laser ELFIE at LULI with a pulse length of ≈350 fs at an energy of 8 J per pulse are directed onto the target. The results are compared to proton spectra from metal and plastic foils with different thicknesses and show a similarly good performance both in maximum energy as well as in proton number. Thus, this target type is a promising candidate for experiments with high repetition rate laser systems. [ABSTRACT FROM AUTHOR]