On the basis of coupled neutronic/hydrodynamic calculations, we examine the neutron heating effects on the ignition and burn propagation in laser-imploded D-T pellets. The fusionproduced neutrons deposit their energy all over the pellet region since the mean-free-path of the neutron is long. The fraction of neutron energies deposited to the central spark region during the ignition phase is too small to reduce the threshold energy of the laser for ignition. In the burn phase, the neutron heating decreases the maximum compression ratio and accelerates the plasma expansion. The inclusion of neutron heating hence decreases the pellet gain from the value in the case without neutron heating. Calculations neglecting the transport of neutron recoils overestimate the neutron heating rate in the reactor-grade pellets.

Experiments are presented that demonstrate the high stopping power of fully ionized hydrogen plasma for low-energy heavy ions. A plasma with electron densities up to 7.1016 cm–3 at temperatures above 1 eV was created by an electrical discharge. In the described experiment, a stopping power of 1.08 GeV/(mg/cm2) was measured using singly charged krypton ions at 45–keV/u energy. The measured stopping power exceeds the corresponding value in cold hydrogen gas by a factor of 35. These measurements confirm the theoretical stopping power predictions close to the expected maximum in a fully ionized plasma.

Energy gain of electron beams in bubble regime of the laser wakefield accelerator can be optimized by improving the acceleration length, radial accelerating and focusing force, number of monoenergetic electrons trapped inside the bubble, and increasing dephasing length. In order to enlarge the dephasing length, the phase velocity of the plasma wave can be increased by optimizing the plasma density profile. We report the estimation of dephasing length using plasma density distribution with the flat and linear-upward profile using two-dimensional particle-in-cell simulations. The size of wakefield bubble depends on the plasma density. With a positive plasma density gradient, the size of bubble decreases. The front and trail part of wake bubble will have different phase velocity in plasma density gradient region. After density transition in constant density region, the bubble elongates and the velocity of the back part of the bubble increases so that the accelerated electron phase synchronizes with the phase of the plasma wave. In a result, the electron acceleration length enhances to improve the beam quality.

Strong electromagnetic fields are radiated during the operation of the intense electron-beam accelerator (IEBA), and it is investigated in this paper. It is obtained that the triggered spark-gap switch and the main switch of the IEBA are the radiation resources. Here, the radiation of the triggered spark-gap switch is researched carefully. Firstly, circuit simulation is used to simulate the current going through the switch. The electric fields generated by the current and its frequency spectra are both calculated. The electric fields of the IEBA are measured by using a bi-cone antenna. When the primary capacitor of the IEBA is charged to 20 kV, the radiation field with amplitude of 753.4 V/m, dominant frequency of 20.8 MHz and high frequency 100 MHz is obtained. The experiment results show reasonable agreements with the analysis. It is believed that the gas-gap switch is a new method to achieve wide-band radiation.

In this paper, we have studied the nonlinear laser absorption in a finite-size plasma, using a fully kinetic relativistic 1½-dimensional particle-in-cell simulation code, and shown that the rate in which laser absorption increases depends on the mass ratio (δ = m+/m−) and the equilibrium density ratio (α = n0+/n0− = z−/z+), respectively. This can be attributed to the essential effects of these parameters on the nonlinear phenomena related to the laser absorption such as phase-mixing and laser-scattering process. We have indicated that the reduction of the defined mass and density ratios increases the absorption rate in the finite-size plasma as long as the laser scattering from the plasma is not considerable. Moreover, the study of kinetic phase-space distributions indicates in a specific range of mass and density ratios a large amount of laser energy leads to arise a population of charged particles having directed kinetic energy along the laser direction. These simulation results are expected to be relevant to the experiments on the intense laser–plasma interactions with applications to the particle acceleration and fast ignition concept as well as to the astrophysical environments.

The present work aims to study the influence of relativistic–ponderomotive effects on cross-focusing of two co-propagating high-power hollow Gaussian laser beams [high-power laser beams (HGLBs)] in collisionless plasma. The effective dielectric constant has been derived on account of relativistic–ponderomotive nonlinearity. The phenomenon of cross-focusing for higher-order modes of HGLB is compared for the case when only relativistic nonlinearity is operative in the system and it is seen that the relativistic–ponderomotive effects make the focusing much stronger and relatively faster. The critical curves for various order of HGLB is discussed and compared with the case when only ponderomotive nonlinearity is present and it reveals that in the case of relativistic–ponderomotive case the spot size reduces effectively. The higher-order modes of propagation of HGLB are also found to be governed by the parameter of another propagating HGLB. The present study is useful in determining the propagation dynamics of HGLB.

In inertial confinement fusion experiments, the symmetrical implosion calls for a new scheme: a nonsupported pellet. In this article, the first experiment is conducted using a plastic pellet covered with thin ferromagnetic material. In the system, the digital-phase-lead-compensator takes the position-related signal and processes it to provide a driving signal for the magnetic suspender. The suspended pellet is irradiated by the Gekko XII laser, having its total energy 2700 J with pulse width 800 ps at the wavelength 0.53 μm. The X-ray pinhole photograph confirms the spherically symmetrical implosion at the pellet core. At irradiation, the neutron yield is also observed.

Acceleration-driven fluid mixing is studied here from a theoretical point of view. Considerable progress has been achieved in the understanding of mix. Theories of the authors are reviewed that allow prediction of the edge of the mixing zone, in agreement with experimental data. Theories that describe the distribution of masses within the mixing region are also reviewed. The theory we present describes a chunk mix regime, in which two phases are mixed at a chunk level, but for which there is no atomic mixing. Thus the two phases are segregated into disjoint regions of space.

In this paper, we are presenting the microwave emission results of a vircator that emits its radiation lying well-within the microwave range of electromagnetic spectrum viz 4–8 GHz and the energy needed per shot is as low as 25 Joules only. In this reported experiment, the pulse forming line is charged to a voltage of 160 kV and the measured diode voltage is 50 kV in the experiment. The primary energy is nearly 50 Joules only and hence the energy efficiency of the high voltage pulse transformer and pulse forming line combination for the given experiment is nearly 50%. The experiment is the first of its kind in establishing (experimentally) the low voltage operation of a conventional vircator, which has a planar cylindrical cathode and stainless steel mesh anode, for the microwave emission purpose. Moreover, because of the low voltage and low energy operation we could operate the whole system in repetitive mode and we could achieve as high as 4 Hz operation with this device. Interestingly, the current density of the velvet cathode used in the present experiment is nearly 300 A/cm2 in the present reported set of experiments. One interesting observation emerging out from the present experiment is that in the low voltage operation of the vircator the beam acceleration potential is relatively low and hence the axial velocities of reflexing electrons (trapped between cathode and virtual cathode) is also limited and far less than 1.8 × 108 m/s and hence with small anode cathode gaps like that of 3 mm, which is the case of present experiments, it becomes feasible to achieve radiation frequency of 4–8 GHz from the vircator.

An electrically calibrated bolometer designed to measure VUV and soft X-ray radiation in tokamaks was installed at the end of the calibration beam line used by CEL-V at the LURE synchrotron. Low-noise electronics and an adequate data acquisition enabled absolute measurements of power densities as low as 1 μW/cm2. Power density measurements are presented. At the same location several soft X-ray detectors used in laser-plasma interaction studies were installed and their absolute calibration was performed (photocathodes, photodiodes, etc.). Calibration results are presented and compared with a Henke model for photocathode response.

In the present article, a number of theoretical approximations and numerical methods, varying in complexity, are reviewed, in order to facilitate their selection for plasma diagnostic purposes. Results refer to highly charged ions, particularly in the lithium isoelectronic sequence. This article describes progress in understanding the role of laser induced degenerate state phenomenon on resonances obtained by using lasers. This type of process, implicitly included in the R-matrix Floquet calculation, contributes to some degree, to the overall behavior of the resonance profiles. The present article gives comparative results obtained from ab initio non-perturbative treatment and perturbative calculation of autoionization widths in Be-like ions. The effective oscillator strength for complex highly ionized atoms is, also, provided. Such calculations are of interest as they represent accurate benchmark data for beam emission spectroscopy, Zeff analysis, or complex atoms modeling in fusion plasma devices.

Bandwidth effects on laser-plasma interaction were investigated with a ¼-μm laser. Planar targets were irradiated with a 1- to 40-cm–1 bandwidth laser at I = 1 × 1013–4 × 1015 W/cm2. Above 3 × 1013 W/cm2, stimulated Brillouin scattering (SBS) was observed with 1 cm–1 light. This process was strongly reduced with a 40-cm–1 light. Evolution of the convective SBS was studied with 1-D fluid simulation code. Bandwidth effect on the SBS growth was discussed to compare the theoretical prediction and experimental results. The scalelength dependence exists for the SBS reduction with a broadband laser.

The time-dependent soft X-ray emission of helium and nitrogen plasmas generated by optical-field ionization is reported. The experiments were carried out by focusing pulses of the high-power Ti:sapphire laser of the Lund Institute of Technology (λ = 796 nm, pulse duration 150 fs, pulse energy 150 mJ) to a 50-μm diameter spot close to a nozzle, using He and N2 as target gases. The emission on He+, N4+, and N3+ resonance lines was recorded by means of a flat-field grating spectrometer coupled to an X-ray streak camera. A pronounced difference in the temporal shape of the emission of the Lyman-α line of hydrogen-like helium and of the 2p−3d resonance lines of lithium-like and beryllium-like nitrogen was observed. The helium line exhibited an initial spike followed by a slow revival of the emission, whereas the nitrogen lines showed a slow decay after a fast initial rise. These observations are explained with the help of simulations.

Plasmas with long life times (∼20 ns) are generated in a cavity target by intense CO2 laser pulses (2 × 1014W/cm2). The plasma life depends on the configuration of irradiation and target, which may infer thermal conduction inhibition by the laser-generated magnetic field. The experimental results agree with those of computer simulations with magnetic inhibition of thermal conduction.

Direct-drive laser fusion received a number of setbacks from the experimental observation in the 1960s and 1970s of very complex interactions in laser plasma experiments caused by a number of nonlinear and anomalous phenomena. Although smoothing methods were introduced intuitively or empirically–succeeding in reducing these difficulties–it was not until a few years ago that the 20-ps stochastic pulsation mechanism was discovered. We assume here that this 20-ps stochastic pulsation may be the major obstacle to achieving direct-drive fusion, even though it is now generally assumed that the major challenge to the achievement of direct-drive fusion is the Rayleigh-Taylor instability. While we do not discount the importance of the Rayleigh-Taylor mechanisms, we concentrate here on the analysis of the pulsation process. A method of analysis was developed, using time-dependent real-time computations employing a genuine two-fluid model, which includes the interior electric fields and the very large amplitude longitudinal plasma oscillations that are driven by the laser field. These mechanisms, which were first suggested in 1974, reveal themselves now as self-generated von-Laue gratings, preventing the propagation of laser radiation through the outermost plasma corona and preventing energy deposition by temporal interruption caused by thermal relaxation and the subsequent reestablishment of these gratings, and so on. The abolition of this pulsation by broad-band laser irradiation or other smoothing methods is now well understood. A synopsis of these developments is presented here, consistent with Rubbia's proposition of using the MJ drivers for laser fusion, the technology for which is now available.

Fundamental parameters are studied for the detailed design of a picosecond high power KrF laser system. The saturation energy density of 2.3 mJ/cm2 and gain recovery time of 1.9 ns in an e-beam pumped KrF laser are observed. A 6 ps pulse is amplified to 1.9 J. The system at the Electrotechnical Laboratory is expected to deliver 10 ps pulses with total energy of several tens of joules in several beams.

As the input power and energy content of Tokamaks are increased, the erosion rate of the first wall becomes larger, and a thick coating or cladding of low atomic number (Z) materials will be needed. Recently, the present authors prepared Si3N4–SiC films at alow temperature of 400°C by a plasma CVD method for the application to coating materials having high strength and wear resistance on metals and glasses. In this study, irradiation damage of the Si3N4–SiC films and 316 stainless steel (SUS-316) was investigated for the application to the first wall materials in a fusion reactor. The damage studies employed an intense pulsed light-ion beam (LIB) from the “ETIGO-I” device.

Laser vacuum acceleration can be optimized significantly by applying a static magnetic field which is along the direction of laser magnetic field. This setup can cause a charged particle to be of a periodic, oscillatory-rising velocity, and significantly high kinetic energy. Moreover, the contribution from the motion vertical to accelerating electric field is fully taken into account and is found to be essential to efficient acceleration.

The concept of fast ignitor is intimately connected with the fundamental phenomenon of ultra-intense light beam propagation through dense matter in which kinetic effects combine with radiation pressure dominated hydrodynamics to form a complex scenario of extremely non-linear physics. In this paper, the fluid dynamic aspect of channel formation in a highly over-dense plasma is studied and possible attenuation mechanisms of the propagating pulse are evaluated in one dimension. Under the assumption that mass ablation reaches a quasistationary state, the radiation-assisted ablation pressure, the speed of the bow shock, and the density steepening around the critical point are determined self-consistently from the ID fluid conservation relations and the electromagnetic wave equation. Due to ponderomotive profile steepening, the ablation pressure is reduced by 40% in the subsonic region and is dominated by the radiation pressure in the supersonic domain. Channel lengths are calculated for various intensities and pellet compression ratios. Likewise, the nonlinear propagation of a superintense electromagnetic wave in an underdense plasma channel is investigated for the ID case with the help of a relativistic fluid model.

Effects of an implosion nonuniformity with [ell ] = 1 ([ell ]: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-Xll glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with [ell ] = 1 was observed in the shape of the accelerated target at the early stage of the implosion. At the final stage of the implosion, the resultant nonuniformity with [ell ] = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity with [ell ] = 1. The experimental results were compared with one-dimensional (1-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with [ell ] = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of [ell ] = 1 only but with multimode nonuniformities such as [ell ] = 1 coupled with some additional middle-mode ones (e.g., [ell ] = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark.