Progress and opportunities for inertial fusion energy in Europe
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
11/2020
Journal Article
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.
Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for ...the performance of inertial confinement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-deflected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a significant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.
Direct production of electron-positron pairs in two-photon collisions, the Breit-Wheeler process, is one of the basic processes in the universe. However, it has never been directly observed in the ...laboratory because of the absence of the intense γ-ray sources. Laser-induced synchrotron sources emission may open a way to observe this process. The feasibility of an experimental setup using a MeV photon source is studied in this paper. We compare several γ-ray sources and estimate the expected number of electron-positron pairs and competing processes by using numerical simulations including quantum electrodynamic effects.
Extremely high pressures (approximately 10 TPa) and temperatures (5 x 10(5) K) have been produced using a single laser pulse (100 nJ, 800 nm, 200 fs) focused inside a sapphire crystal. The laser ...pulse creates an intensity over 10(14) W/cm2 converting material within the absorbing volume of approximately 0.2 microm3 into plasma in a few fs. A pressure of approximately 10 TPa, far exceeding the strength of any material, is created generating strong shock and rarefaction waves. This results in the formation of a nanovoid surrounded by a shell of shock-affected material inside undamaged crystal. Analysis of the size of the void and the shock-affected zone versus the deposited energy shows that the experimental results can be understood on the basis of conservation laws and be modeled by plasma hydrodynamics. Matter subjected to record heating and cooling rates of 10(18) K/s can, thus, be studied in a well-controlled laboratory environment.
Recently achieved high intensities of short laser pulses open new prospects in their application to hole boring in inhomogeneous overdense plasmas and for ignition in precompressed DT fusion targets. ...A simple analytical model and numerical simulations demonstrate that pulses with intensities exceeding 10;{22} W/cm;{2} may penetrate deeply into the plasma as a result of efficient ponderomotive acceleration of ions in the forward direction. The penetration depth as big as hundreds of microns depends on the laser fluence, which has to exceed a few tens of GJ/cm;{2}. The fast ions, accelerated at the bottom of the channel with an efficiency of more than 20%, show a high directionality and may heat the precompressed target core to fusion conditions.
We attribute a strong forward directed THz emission from femtosecond laser filaments in air to a transition-Cherenkov emission from the plasma space charge moving behind the ionization front at light ...velocity. Distant targets can be easily irradiated by this new source of THz radiation.
Collisionless shocks are ubiquitous in the Universe as a consequence of supersonic plasma flows sweeping through interstellar and intergalactic media. These shocks are the cause of many observed ...astrophysical phenomena, but details of shock structure and behavior remain controversial because of the lack of ways to study them experimentally. Laboratory experiments reported here, with astrophysically relevant plasma parameters, demonstrate for the first time the formation of a quasiperpendicular magnetized collisionless shock. In the upstream it is fringed by a filamented turbulent region, a rudiment for a secondary Weibel-driven shock. This turbulent structure is found responsible for electron acceleration to energies exceeding the average energy by two orders of magnitude.
Quasi-static magnetic-fields up to 800 T are generated in the interaction of intense laser pulses (500 J, 1 ns, ) with capacitor-coil targets of different materials. The reproducible magnetic-field ...peak and rise-time, consistent with the laser pulse duration, were accurately inferred from measurements with GHz-bandwidth inductor pickup coils (B-dot probes). Results from Faraday rotation of polarized optical laser light and deflectometry of energetic proton beams are consistent with the B-dot probe measurements at the early stages of the target charging, up to ns, and then are disturbed by radiation and plasma effects. The field has a dipole-like distribution over a characteristic volume of 1 mm3, which is consistent with theoretical expectations. These results demonstrate a very efficient conversion of the laser energy into magnetic fields, thus establishing a robust laser-driven platform for reproducible, well characterized, generation of quasi-static magnetic fields at the kT-level, as well as for magnetization and accurate probing of high-energy-density samples driven by secondary powerful laser or particle beams.
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