We focus attention on the combinations of swiftly growing electromagnetic instabilities (EMI) arising in the interaction of relativistic electron beams (REB) with precompressed deuterium-tritium (DT) fuels of fast ignition interest for inertial confinement fusion (ICF). REB-target system is taken neutral in charge and current with distribution functions including target and beam temperatures. We stress also the significant impact on modes growth rates (GR) of mode-mode coupling and intrabeam scattering. Collisional damping is documented at large wave numbers in terms of inverse skin depth. A quasi-linear approach yields lower GR than linear ones. One of the most conspicuous output of the linear analysis are three-dimensional (3D) broken ridges featuring the largest GR above k-space for an oblique propagation w.r.t initial particle beam direction. The given modes are seen immune to any temperature induced damping. Those novel patterns are easily produced by considering simultaneously Weibel, filamentation and two-stream instabilities. The behaviors persist in the presence of smooth density gradients or strong applied magnetic fields. Moreover, in the very early propagation stage with no current neutralization in the presence of large edge density gradients, REB demonstrate a characteristics ringlike and regularly spiked pattern in agreement with recent experimental results and previous simulations.

Quasi-monoenergetic electron beams of energies 12 MeV to over 200 MeV are generated from both nitrogen and helium gas targets with 7TW laser pulses. Typically nitrogen gas interactions lead to electron bunches in the range of 12 to 50 MeV varying from shot to shot. Helium gas leads to higher energy electron bunches from 25 to 100 MeV. Occasionally exceptionally high energy bunches of electrons up to 200 MeV are observed from nitrogen and helium. Initial full two-dimensional simulations indicate the production of 20–30 MeV electron energy bunches for the typical interaction conditions as the electrons are injected from wave breaking in the plasma wake behind the laser pulse and injected into the strong electric field gradient propagating with the optical pulse. This is consistent with the experimental observations from the majority of shots. Pulse compression during propagation in the high density plasma does not allow the threshold conditions for the full bubble regime to be reached. However, the electric acceleration field in the wakefield cavity is still sufficient to lead to the formation of a bunch of electrons with an energy peak in the range of 20 to 30 MeV. In order to explain the occasional high energy shots most likely a lower density channel created by the laser prepulse may occasionally form a natural low density electron guide channel giving ideal conditions for acceleration over much longer lengths leading to the high energies observed.

One of the most exciting results recently obtained in the ultraintense interaction research area is the observation of beams of protons with energies up to several tens of megaelectron volts, generated during the interaction of ultraintense picosecond pulses with solid targets. The particular properties of these beams (high brilliance, small source size, high degree of collimation, short duration) make them of exceptional interest in view of diagnostic applications. In a series of experiments carried out at the Rutherford Appleton Laboratory (RAL) and at the Lawrence Livermore National Laboratory (LLNL), the laser-produced proton beams have been characterized in view of their application as a particle probe for high-density matter, and applied to diagnose ultraintense laser–plasma interactions. In general, the intensity cross section of a proton beam traversing matter will be modified both by collisional stopping/scattering, and deflections caused by electric/magnetic fields. With a suitable choice of irradiation geometry and target parameters, the proton probe can be made mainly sensitive to the electric field distribution in the object probed. Therefore, point projection proton imaging appears as a powerful and unique technique for electric field detection in laser-irradiated targets and plasmas. The first measurements of transient electric fields in high-intensity laser-plasma interactions have been obtained with this technique.

Fokker-Planck (FP) codes have become useful tools for modeling nonlocal heat-transport phenomena in laser-produced plasmas. Several possible simplifications to the FP equation as well as different numerical techniques available for its solution are investigated. The most robust and efficient approach is found to involve the diffusive approximation of the FP equation and the alternating-direction-implicit method of solution. The SPARK FP code, which has been developed along these principles, is described in detail. It incorporates fluid ions and solves for transport on either a two-dimensional Eulerian grid or a one-dimensional Lagrangian grid. Sample simulation results are presented, together with a discussion of possible improvements to the code.

In this paper we discuss the importance of radiation transport in inertial confinement fusion (ICF) target design. It is shown that a self similar solution of non-linear heat conduction can be used to estimate the penetration depth of radiation thermal waves (Marshak Waves) in ion-beam ICF pellets. An improved numerical treatment of non-linear heat conduction has been incorporated into the hydrodynamic code MEDUSA-KA to simulate radiation transport in ICF target design studies. The numerical results have been checked against self-similar solutions and a comparison between the two is presented in this paper. We find good agreement between the two. The necessity of using a high-z radiation shield to protect the fuel from radiative preheat is also discussed.

The inertial confinement fusion (ICF) philosophy is based on high compression. The reasoning is that (a) it is cheaper (energetically) to compress than to heat and (b) nuclear reactions are proportional to density square, therefore the more you compress the better you are in ICF. Of course the only limitations of compression are the hydrodynamic instabilities (like Rayleigh-Taylor, etc). Many of the references in the literature require extremely high compression and in particular the pB11 needs extremely huge compressions. In this paper it is shown that there is an optimum of compression, namely gain G is maximum for a definite compression. The value of this density (for a given fuel mass and particular ICF scheme) depends on the equation of state (EOS). We calculate this value for fast ignition (FI) schemes and compare it with the central spark ignition (CSI) model. The gain calculations are based on the ideal gas for the ions and the Fermi-Dirac EOS for the electrons with an effective alpha, as usually suggested from simulations. The “optimum compression” idea is easily understood from the following argument: From EOS data one needs an infinite energy to compress to an infinite density. Since the energy output is finite it is clear that G is zero for infinite compression. On the other hand for normal density with small fuel mass (~ few mg) the gain is also zero. Therefore a maximum should exist somewhere. For the deuterium-tritium fuel with a mass of few mg one gets an optimum at few hundred g/cc. If you compress more then the gain is going down. So there is a desired maximum compression fixed by EOS. Last but not least, bremsstrahlung losses in degenerate plasma are discussed and the clean fusion (i.e., without neutrons) of proton + B11 → 4α is analyzed.

A scheme of terahertz radiation generation is proposed by beating of two extra-ordinary lasers having frequencies and wave numbers $\lpar {\rm \omega}_1\comma \; \vec k_1 \rpar $ and $\lpar {\rm \omega}_2\comma \; \vec k_2 \rpar $, respectively in a magnetized plasma. Terahertz wave is resonantly excited at frequency $\lpar {\rm \omega}_1 - {\rm \omega}_2 \rpar $ and wave number (k1 − k2 + q) with a wave number mismatch factor q which is introduced by the periodicity of plasma density ripples. In this process, the lasers exert a beat ponderomotive force on plasma electrons and impart them an oscillatory velocity with both transverse and longitudinal components in the presence of transverse static magnetic field. The oscillatory velocity couples with density ripples and produces a nonlinear current that resonantly excites the terahertz radiation. Effects of periodicity of density ripples and applied magnetic field are analyzed for strong THz radiation generation. The terahertz radiation generation efficiency is found to be directly proportional to the square of density ripple amplitude and rises with the magnetic field strength. With the optimization of these parameters, the efficiency ~10−3 is achieved in the present scheme. The frequency and power of generated THz radiation can be better tuned with the help of parameters like density ripple amplitude, periodicity and applied magnetic field strength in the present scheme.

This paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titanium-sapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fs radiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifier is created in a XeF2/N2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of first experiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented to demonstrate that a laser beam peak power of 14 TW has been attained.

We present our results on spatio-temporal evolution of laser plasma produced shockwaves (SWs) and hot core plasma (HCP) created by focused second harmonic (532 nm, 7 ns) of Nd-YAG laser in quiescent atmospheric air at f/#10 focusing geometry. Time resolved shadowgraphs imaged with the help of an ICCD camera with 1.5 ns temporal resolution revealed the presence of two co-existing sources simultaneously generating SWs. Each of the two sources independently led to a spherical SW following Sedov-Taylor theory along the laser propagation direction with a maximum velocity of 7.4 km/s and pressure of 57 MPa. While the interaction of SWs from the two sources led to a planar SW in the direction normal to the laser propagation direction. The SW detaches from the HCP and starts expanding into the ambient air at around 3 µs indicating the onset of asymmetric expansion of the HCP along the z-axis. The asymmetric expansion is observed till 10 µs beyond which the SW leaves the field of view followed by a deformation of the irradiated region in the XY-plane due to the penetration of surrounding colder air in to the HCP. The deformation in the XY-plane lasts till 600 µs. The dynamics of rapidly expanding HCP is observed to be analogous to that of cavitation bubble dynamics in fluids.

We perform the analysis of the Rayleigh–Taylor instability of thin perfectly elastic solid plates using the analytical approach recently developed by Piriz and coworkers. The model describes the evolution of the perturbation amplitude from the initial conditions and at relatively long times it yields the asymptotic growth rate. It applies to solid/inviscid fluid interfaces. For the particular case of solid/vacuum interface, the model has been compared with the exact results by Plohr and Sharp and an excellent agreement has been found. In general, thinner plates are found to be more unstable and, in the presence of a fluid below the elastic plate, the growth rate is reduced.

A relativistically intense short laser pulse can produce a large flux of X rays through the interaction with electrons that are driven by its intense electromagnetic fields. Apart from X rays from the high-Z matter irradiation by an intense laser, two main processes, Larmor and Bremsstrahlung radiation, are among the most significant mechanisms for X-ray emission from short-pulse laser irradiation on low-Z matter in the regime of relativistic intensities. We evaluate the power, energy spectrum, brilliance, polarization, and time structure of these X rays. We suggest a few methods that significantly enhance the power of Larmor X rays. Because of the peakedness in the energy spectrum of Larmor X rays, Larmor X rays have important applications.

We derive optimum values of parameters for laser-driven flights into low Earth orbit (LEO) using an Earth-based laser, as well as sensitivity to variations from the optima. These parameters are the ablation plasma exhaust velocity vE and specific ablation energy Q*, plus related quantities such as momentum coupling coefficient Cm and the pulsed or continuous laser intensity that must be delivered to the ablator to produce these values. Different optima are found depending upon whether it is desired to maximize mass m delivered to LEO, maximize the ratio m/M of orbit to ground mass, or minimize cost in energy per gram delivered. Although it is not within the scope of this report to provide an engineered flyer design, a notional, cone-shaped flyer is described to provide a substrate for the discussion and flight simulations. The flyer design emphasizes conceptually and physically separate functions of light collection at a distance from the laser source, light concentration on the ablator, and autonomous steering. Approximately ideal flight paths to LEO are illustrated beginning from an elevated platform. We believe LEO launch costs can be reduced 100-fold in this way. Sounding rocket cases, where the only goal is to momentarily reach a certain altitude starting from near sea level, are also discussed. Nonlinear optical constraints on laser propagation through the atmosphere to the flyer are briefly considered.

Ag thin films were deposited by pulsed laser ablation in a controlled Ar atmosphere. The deposition process was performed at different Ar pressure values in the range between 10 and 100 Pa to investigate the influence of ambient gas pressure on the plasma expansion dynamics and on the film structural properties. Position, velocity and volume of the laser generated plasma as functions of time were obtained by time resolved fast photography. The morphological properties of the films were investigated by transmission electron microscopy which shows that film growth proceeds via aggregation on the substrates of nanoclusters formed in the expanding plume. The formation of nanoparticles takes place as a consequence of plasma confinement induced by the interaction with ambient gas species. Data from fast photography analysis were used as input parameters to calculate the size of the nanoparticles using a model that takes into account the collisional nature of the laser generated silver plasma.

In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.

In this article, we present a laboratory astrophysics experiment on radiative shocks and its interpretation using simple modelization. The experiment is performed with a 100-J laser (pulse duration of about 0.5 ns) which irradiates a 1-mm3 xenon gas-filled cell. Descriptions of both the experiment and the associated diagnostics are given. The apparition of a radiation precursor in the unshocked material is evidenced from interferometry diagrams. A model including self-similar solutions and numerical ones is derived and fairly good agreements are obtained between the theoretical and the experimental results.

The nonlinear stage in the growth of the Rayleigh-Taylor instability in three dimensions (3D) is studied using a 3D multimaterial hydrodynamic code. The growth of a single classical 3D square and rectangular modes is compared to the growth in planar and cylindrical geometries and found to be close to the corresponding cylindrical mode, which is in agreement with a new Layzer-type model for 3D bubble growth. The Atwood number effect on the final shape of the instability is demonstrated. Calculations in spherical geometry of the late deceleration stage of a typical ICF pellet have been performed. The different late time shapes obtained are shown to be a result of the initial conditions and the high Atwood number. Finally, preliminary results of calculations of two-mode coupling and random perturbations growth in 3D are presented.

The short D-D distance of 2.3 pm in the condensed material ultra-dense deuterium means that it is possible that only a small disturbance is required to give D+D fusion. This disturbance could be an intense laser pulse. The high excess kinetic energy of several hundred eV given to the deuterons by laser induced Coulomb explosions in the material increases the probability of spontaneous fusion without the need for a high plasma temperature. The temperature calculated from the normal kinetic energy of the deuterons of 630 eV from the Coulomb explosions is 7 MK, maybe a factor of 10 lower than required for ignition. We now report on experiments where several types of high-energy particles from laser impact on ultra-dense deuterium are detected by plastic scintillators. Fast particles with energy up to 2 MeV are detected at a time-of-flight as short as 60 ns, while neutrons are detected at 50 ns time-of-flight after passage through a steel plate. A strong signal peaking at 22.6 keV u−1 is interpreted as due to mainly T retarded by collisions with H atoms in the surrounding cloud of dense atomic hydrogen.

Plasma-based accelerators have been proposed for the next generation of compact accelerators because of the huge electric fields they can support. However, it has been difficult to use them efficiently for applications because they produce poor quality particle beams with large energy spreads. Here, we demonstrate a dramatic enhancement in the quality of electron beams produced in laser-plasma interaction: an ultrashort laser pulse drives a plasma bubble which traps and accelerates plasma electrons to a single energy. This produces an extremely collimated and quasi-monoenergetic electron beam with a high charge of 0.5 nanocoulomb at energy 170 ± 20 MeV.

It was reported that the fuel core was heated up to ∼0.8 keV in the fast ignition experiments with cone-guided targets, but they could not theoretically explain heating mechanisms and achievement of such high temperature. Thus simulations should play an important role in estimating the scheme performance, and we must simulate each phenomenon with individual codes and integrate them under the fast ignition integrated interconnecting code project. In the previous integrated simulations, fast electrons generated by the laser-plasma interaction were too hot to efficiently heat the core and we got only 0.096 keV rise of temperature. Including the density gap at the contact surface between the cone tip and the imploded plasma, the period of core heating became longer and the core was heated by 0.162 keV, ∼ 69% higher increment compared with ignoring the density gap effect.

This paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort (<100 ps) avalanche electron beam is formed in the solid angle more than 2π steradian. The electron beam has been obtained behind a 45 µm thick Al-Be foil in SF6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.