The single-beam Asterix IV high-power iodine laser, presently operated at a pulse length of 0.3 ns, has achieved its projected output power of 4 TW. It is designed to deliver output pulses with lengths ranging from 0.1–3 ns with a maximum power of 5 TW and an energy of up to 2 kJ. This laser has been developed on the basis of 10 years of experience with the 1 TW Asterix III laser and with the support of a 1-D and 3-D pulse propagation code. Special emphasis has been put on increasing the overall efficiency of the laser system and obtaining a laser beam intensity profile as homogeneous as possible. In this article, the measures for improving the laser performance and the results obtained hitherto are presented.

Interactions of laser driven plasma jets with He and Ar gas puffs was investigated experimentally by means of three-frame interferometric/shadowgraphic system and three-frame X-ray pinhole camera. A defocused iodine laser beam using the Prague Asterix Laser System (PALS) interacting with massive planar Cu targets generated high-speed well-collimated plasma jets. The PALS third harmonic (0.438 µm), with pulse duration of 250 ps (full width at half maximum), and energy of 100 J was employed in two irradiation geometries: with an incidence normal to the target surface and with an oblique one (30° with respect to the target normal), in order to minimize the heating of the ambient gas by the laser beam. The results of these interaction experiments, in particular, those obtained in case of the oblique incidence geometry, are presented and discussed. They show the effect of the double shock formation in ambient gases: starting by the ablative plasma action, followed by that of the jet.

We used X-ray spectroscopy as a diagnostic tool for investigating the properties of laser-cluster interactions at the stage in which non-adiabatic cluster expansion takes place and a quasi-homogeneous plasma is produced. The experiment was carried out with a 10 TW, 65 fs Ti:Sa laser focused on CO2 cluster jets. The effect of different laser-pulse contrast ratios and cluster concentrations was investigated. The X-ray emission associated to the Rydberg transitions allowed us to retrieve, through the density and temperature of the emitting plasma, the time after the beginning of the interaction at which the emission occurred. The comparison of this value with the estimated time for the “homogeneous” plasma formation shows that the degree of adiabaticity depends on both the cluster concentration and the pulse contrast. Interferometric measurements support the X-ray data concerning the plasma electron density.

An anti-resonance pulse forming network (PFN) has been designed, analyzed, and tested for its application in generating quasi-square pulses. According to the circuit simulations, a compact generator based on two/three-section network was constructed. Two-section network is applied in the generator due to its compact structure, while three-section network is employed for generating pulses with higher quality. When two-section network is applied in the generator, the full-width at half-maximum of the load pulse is 400 ns, at the same time, its rise time, flat top and fall time are 90, 180 and 217 ns, respectively. When the three-section network is applied with the same pulse width of the load pulse, the rise time of the output decreases to 60 ns, while the flat top increases to 240 ns and the fall time reduces to 109 ns. Meanwhile, this kind of network could be used to shape the output pulses of generators whose equivalent circuit is LC series discharge network, such as MARX generator, into quasi-square pulses. And the preliminary experiment demonstrates that anti-resonance network could work well on four-stage Marx generators. A sine pulse generated by the four-stage Marx generator is shaped into a quasi-square pulse with voltage of 11.8 kV and pulse width about 110 ns based on two-section anti-resonance network.

The shock waves in laser plasma interaction have played an important role in the study of inertial fusion energy (IFE) since the 1970's and perhaps earlier. The interaction of laser, or any other high power beam, induced shock waves with matter was one of the foundations of the target design in IFE. Even the importance of shock wave collision was studied and its importance forgotten. In due course, the shock waves were taken as granted and became “second fiddle” in IFE scenario. The analysis of the shock wave in the context of IFE is revived in this paper. At the forefront of the past decade the concept of fast ignition was introduced. The different ideas of fast ignition are summarized with special emphasis on shock wave fast ignition. The ignition is achieved by launching a shock wave during the final stages of the implosion. In this paper, a possible instability in the propagation of the igniting shock wave is analyzed. The idea of combining the fast ignition fusion with an impact shock wave is suggested and analyzed. This is achieved by launching a shock wave by an accelerated foil during the final stage of the implosion in order to ignite the compressed fuel. In this scheme, like other fast ignition schemes, a significant reduction of the driver energy in comparison with standard IFE scenarios is required for the same high gain fusion.

A theoretical model for the prolongation of lifetime of a gaseous plasma channel formed by two pulse technique at laser intensities below the tunnel ionization threshold is developed. The first laser pulse ionizes the gas completely on the axis and partially off the axis, causing self-defocusing of the pulse. After the passage of the pulse, the plasma expands radially, creating an atom/ion density profile with a minimum on the axis. Partial recombination also sets in. As the second pulse arrives, after a time delay of less than the recombination time (~ns), the electrons get heated, and the recombination rate is slowed down. The second pulse self focuses, enhancing the heating rate and lengthening the lifetime of the plasma channel.

A plasma model of the origin of the light elements and the microwave background is presented. In contrast to the conventional Big Bang hypothesis, the model assumes that helium, deuterium and the microwave background were all generated by massive stars in the early stages of galaxy formation. The microwave background is scattered and isotropized by multi-GeV electrons trapped in the jets emitted by active galactic nuclei. The model produces reasonable amounts of heavy elements, accurately predicts the gamma-ray background intensity and spectrum, and explains the statistics of quasars, compact and extended radio sources.

Mirror like Molybdenum thin films on SS substrate in vacuum (10−3 Pa) and in Helium environment has been achieved by Pulsed Laser Deposition (PLD) Technique. The PLD thin films of Molybdenum have been characterized by using X-ray Diffraction (XRD) pattern, Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Energy Dispersive X-ray (EDX). The specular reflectivity was recorded with Fourier Transform Infra-Red spectrometer and UV-Visible spectrometer. The optical quality of the thin films was tested via interferometric technique. At the optimum deposition parameters, the crystal orientation was in Mo(110) phase. The FIR-UV-Visible reflectivity of the mirror was found to be closed to that of the polished bulk Molybdenum and Stainless Substrate (SS) substrate.

High intensity fs-laser pulses can deliver focused intensities in the region of 1016–1019 W/cm2. If the laser pulse is focused onto a solid or gaseous material, a plasma is created. The electrons, as well as the ions are accelerated in the strong laser field up to energies in the range of keV to several MeV. The interaction of the high energy particles with cold material, that is, the solid target yield of intense X-ray emission, K-shell—as well as bremsstrahlung-radiation. The K-shell emission from layered targets is a useful indicator of the production efficiency, energy distribution, and transport of hot electrons produced in fs-laser plasmas. For the diagnosis of laser plasma interaction and its application as an intense X-ray source, the spatial, temporal and spectral distribution of K-shell X rays is of fundamental importance. Focusing crystal spectrographs can be used to obtain a single shot X-ray spectra of laser plasmas produced by table top fs-lasers. With a spatial- and spectral-focusing spectrograph based on a toroidally bent crystal, the emission region of the hot plasma and Kα-radiation can be determined. Recording the spectra online by a frontside illuminated charge-coupled device (CCD) allows alignment of the crystal spectrograph, as well as the laser beam focusing leading to different X-ray source sizes. Using a controlled fs-prepulse, an increase in Kα radiation could be observed with the diagnostic.

Measurements of calibrated high resolution spectra are compared with particle-in-cell (PIC) calculations of the laser absorption and hot electron production postprocessed by a Monte–Carlo (MC) transport model of electron stopping and Kα X-ray generation.

Dielectric functions of an electron plasma are calculated for an electron gas in which number, momentum, and energy are conserved during electron-electron collisions. They are compared with others in the literature, revealing that, in general, that imposition of the conservation laws tends to make the full conserving dielectric response more similar to the random phase approximation dielectric response than without it. This is due to the fact that in the random phase approximation model all the conservation laws are also enforced. Our model is checked for other plasma degeneracies; concretely we consider partially degenerate plasmas and classical plasmas. The behaviour of the dielectric functions of these plasmas is similar to the degenerate one. Differences among dielectric functions are more significant than for the degenerate case, but it is mainly due to low relaxation time values. The most relevant issue for these plasmas is the fact that the consideration of energy conservation in the dielectric function is more important in these cases, because plasma temperature is significant.

In order to realize an effective implosion, the beam illumination non-uniformity and implosion non-uniformity must be suppressed to less than a few percent. In this paper, a direct-indirect mixture implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement (dz) in a reactor. In a direct-driven implosion mode dz of ∼20 μm was tolerance and in an indirect-implosion mode dz of ∼100 μm was allowable. In the direct-indirect mixture mode target, a low-density foam layer is inserted, and radiation is confined in the foam layer. In the foam layer the radiation transport is expected in the lateral direction for the HIB illumination non-uniformity smoothing. Two-dimensional implosion simulations are performed and show that the HIB illumination non-uniformity is well smoothed. The simulation results present that a large pellet displacement of ∼300 μm is tolerable in order to obtain sufficient fusion energy in HIF.

This paper presents a scheme of THz generation by nonlinear photomixing of two cosh-Gaussian lasers pulses having different frequencies (ω1, ω2) and wave numbers $(\vec k_1, \vec k_2 )$ and same electrical field amplitude in a corrugated plasma embedded with transverse static magnetic field. Cosh-Gaussian laser pulses have steep gradient in intensity profile along with wider cross-section, which exerts a stronger nonlinear ponderomotive force at ω1 − ω2 and $\vec k_1 - \vec k_2 $ on plasma electrons imparting a nonlinear oscillatory velocity to plasma electrons. Oscillatory plasma electrons couple with the density ripple n′ = nα0eiαx to produce a nonlinear current, which is responsible for resonant THz radiation at frequency $\sim\left( {{\rm \omega} _{\rm c}^2 + {\rm \omega} _{\rm p}^2} \right)^{1/2} $. The amplitude, efficiency and beam quality of THz radiation can be optimized by choosing proper corrugation factor (α of the plasma), applied magnetic field (ωc), decentered parameter (b), and beam width parameter a0 of cosh-Gaussian lasers. An efficiency of $\sim\!10^{ - 2} - 10^{ - 1} $ is achieved for laser electric field E = 3.2 × 109 V/cm.

Hollow microcylinder targets, 200–300 μm in diameter, have been internally irradiated at up to 5 · 1014 W/cm2 with Nd:glass laser pulses directed through an axial entrance slit. The plasma evolution in the interior of the cavities was diagnosed with a pinhole imaging X-ray streak camera and a Nomarski-type interferometer. Plasma collision near the center of the cylinder is observed about 300 ps after the irradiating laser pulse. The experimental results are confirmed by a one-dimensional Eulerian fluid code.

In this report, we discuss the physical concept and the results of mathematical modeling of free-standing target (FST) layering for inertial confinement fusion (ICF), including the detailed descriptions of the heat transfer and layer symmetrization mechanisms.

We develop a theoretical model for terahertz (THz) radiation generation, when an intense short laser pulse (ω1, k1) is mixed with its frequency shifted second harmonic (ω2, k2), where ω2 = 2ω1 + ωT and ωT is in the THz range in the plasma. The lasers exert a ponderomotive force on the electrons and drive density perturbations at (2ω1, 2k1) and (ω2 − ω1, k2 − k1). These density perturbations couple with the oscillatory velocities of the electron due to the lasers and produce a nonlinear current at (ω2 − 2ω1, k2 − 2k1). This current acts as an antenna to produce the THz radiation. The THz power depends upon the square of plasma density and $I_1^2 {I_2}$, where I1 and I2 are the intensities of fundamental and second harmonic laser. The radiation is mainly along the forward direction. Two-dimensional particle-in-cell simulations are used to study the near-field radiation properties.

This report addresses the physical concept and the results of mathematical modeling of cryogenic layer degrading caused by its radiation heating during direct drive target injection into the reaction chamber. Special attention is paid to the influence of a solid layer structure on the roughening of the layer surface that is of critical importance for the development of target injection scenario.

The self-focusing of an intense right circularly polarized Gaussian laser pulse in magnetized plasma is studied. The ions are taken to be immobile and relativistic mass effect is incorporated in both the plasma frequency (ωp) and the electron cyclotron frequency (ωc) while determining the ponderomotive force on electrons. The ponderomotive force causes electron expulsion when the effective electron cyclotron frequency is below twice the laser frequency. The nonlinear plasma dielectric function due to ponderomotive and relativistic effects is derived, which is then employed in beam-width parameter equation to study the self-focusing of the laser beam. From this, we estimate the importance of relativistic self-focusing in comparison with ponderomotive self-focusing at moderate laser intensities. The beam width parameter decreases with magnetic field indicating better self-focusing. When the laser intensity is very high, the relativistic gamma factor can be modeled as ${\rm \gamma} = 0.8\left({{{{\rm \omega} _c } / {\rm \omega} }} \right)+ \sqrt {1 + a_0^2 }$$\text{γ}=0.8({\text{ω}}_c/\text{ω})+\sqrt{1+a_0^2}$ where ω and a0 are the laser frequency and the normalized laser field strength, respectively. The cyclotron effects on the self-focusing of laser pulse are reduced at high field strengths.

The Super Proton Synchrotron (SPS) will serve as an injector to the Large Hadron Collider (LHC) at CERN as well as it is used to accelerate and extract proton beams for fixed target experiments. In either case, safety of operation is a very important issue that needs to be carefully addressed. This paper presents detailed numerical simulations of the thermodynamic and hydrodynamic response of solid targets made of copper and tungsten that experience impact of a full SPS beam comprized of 288 bunches of 450 GeV/c protons. These simulations have shown that the material will be seriously damaged if such an accident happens. An interesting outcome of this work is that the SPS can be used to carry out dedicated experiments to study High Energy Density (HED) states in matter.

A numerical and analytical estimation and a one-dimensionalhydrodynamic simulation show that a 30%reduction of the tritium content in a D-T pellet still gives sufficient energy output in aD-T inertial confinement fusion reactor.In other words, the tritiumb content can be reduced significantly without a significant reduction in the D-T fusion energy output.This new result also meansthat the tritium inventory can be reduced significantly before and during the reactor operation in the D-T inertial confinement fusion.This result comes from the contribution of a D-D reaction to the D-T reaction.

Implosions using inertial confinement fusion must be highly symmetric to achieve ignition on the National Ignition Facility. This requires precise control of the drive symmetry from the radiation incident on the ignition capsule. For indirect drive implosions, low mode residual perturbations in the drive are generated by the laser-heated hohlraum geometry. To diagnose the drive symmetry, previous experiments used simulated capsules by which the self-emission X-rays from gas in the center of the capsule during the implosion are used to infer the shape of the drive. However, those experiments used hohlraum radiation temperatures higher than 200 eV (Hauer et al., 1995; Murphy et al., 1998a, 1998b) with small NOVA scale hohlraums under which conditions the symcaps produced large X-ray signals. At the foot of the NIF ignition pulse, where controlling the symmetry has been shown to be crucial for obtaining a symmetric implosion (Clark et al., 2008), the radiation drive is much smaller, reducing the X-ray emission from the imploded capsule. For the first time, the feasibility of using symcaps to diagnose the radiation drive for low radiation temperatures, <120 eV and large 0.7 linear scales NIF Rev3.1 (Haan et al., 2008) vacuum hohlraums is demonstrated. Here we used experiments at the Omega laser facility to demonstrate and develop the symcap technique for tuning the symmetry of the NIF ignition capsule in the foot of the drive pulse.