The collisional recombination process in highly ionized plasma and relevant reheating of the plasma are analyzed in the parameter regime appropriate for X-ray lasing. A method for describing the rate of collisional recombination is proposed based on a compact threelevel atomic model. Reheating of the plasma due to collisional recombination is described by a time-dependent adiabatic exponent γ. Using a self-similar description of the free expanding plasma, the gain of recombination lasing is investigated. In comparison with an open two-level atomic model, the present model gives lower gains appearing later in time. The inclusion of plasma reheating reduces the peak gain and shifts it to later times. Although the three-level model is shown to give a good qualitative description of the atomic processes, a considerable discrepancy was observed when compared with simulations for hydrogenlike carbon.

One of the most crucial problems of a heavy ion fusion (HIF) driver is the transport of the beam from the final focusing system to the fusion target. The conventional focusing scheme is based on ballistic transport, assuming that all space charge effects can be kept sufficiently small. To achieve a space charge neutralized beam transport, other more sophisticated schemes like beam transport in a plasma channel have been suggested. Inspired by the results of the first experiments on the generation of adequate discharge-driven plasmas, we suggest applying a pulsed supersonic gas jet for the high-current discharge channel creation, thereby improving the plasma channel stability. The supersonic jet is produced by a gas expansion into the reactor chamber through a converging-diverging nozzle that has a hollow inner tube on its axis for both heavy ion and UV laser beam injection.

An injection-locking excimer laser beam with a pulse duration of 25 ns is focused on the surface of a polymide film. The laser beam that passes through the etching film is shorter than the original one. By optimizing the thickness of the film and the beam powerdensity, a pulse with a 3-ns pulse duration can be obtained using this switch technology.

The design and constructional aspects of a novel pulse power generator for use in dense plasma research presently under construction are presented. The generator consists of two Marx capacitor banks, each of 0.25 μF, 480 kV, and 28.8 kJ. Each Marx generator drives a water transmission line, in which the live electrode is the central conductor. The transmission lines consist of a constant impedance section followed by a multielectrode gas linegap followed by an exponential taper to the load section. The novel feature is the use of an auxiliary exponential line coupled at the load. This line controls both the voltage and the effective impedance at the load section. In addition, by leaving this line circuit open, energy not coupled to the plasma in the initial high-impedance phase may be reflected back and deposited into the discharge, increasing the peak current by 50%. Circuit simulations using a real-time-varying load impedance show that the current pulse rises in an approximately linear way to a maximum of 1.2 MA at 250 ns. The current falls to zero in the following 250 ns. The current waveform may be flattened simply by disconnecting the auxiliary line, giving a rectangular pulse of 350 ns with a maximum value of 950 kA. The overall impedance of the entire system may be adjusted by varying the separation between the conductors. The equivalent source impedance at the load is 0.8 Ω. This low value is by virtue of the auxiliary line, which limits the voltage at the load section and reduces the insulator constraints. We present simulations of the generator under real load conditions. The model also is checked against analytical solutions of exponential line behavior and against other published models of pulse power generators.

A fast-charging, discharge-switch-free Blumlein pulse forming line has been developed for high-voltage pulsed power generation. In the BL, a saturable charging inductor (CI) of amorphous metallic core is utilized and, as a result, fast-charging (charging time ≈220 ns) is obtained with a reduced prepulse. In addition, by using CI as a step-up transformer, the impedance of the output pulse can be converted to 4Z, Z, Z/4. By using the BL with a Marx generator of 300 kV and 1.1 kJ, an output of —580 kV at 24 kA and a pulse length of 60 ns are obtained, with a current rise time of less than 16 ns. The energy transfer efficiency of the line (output pulse energy/charging energy of a pulse forming line) is evaluated to be more than 92%.

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.

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.

A review of work done on laser generated shocks in solids using a high-peak-power Nd:glass laser in the Laser and Plasma Technology Division of the Bhabha Atomic Research Centre is presented in this paper. The 20-J/5-ns Nd:glass laser used in the experiments is able to produce focused laser intensities in the range of 5 × 1011-1013 W/cm2 and a shock pressure in the range of 0.1–5 Mbar. A l-J/100-ps Nd:glass laser is also being developed for laser shock studies, details of which are presented. Several diagnostics have been developed for laser shock studies of which the main diagnostics are optical shadowgraphy, optical interferometry, and laser velocity interferometry for particle velocity measurement. The measurement of ablation pressure in various types of targets, the scaling of ablation pressure with laser intensity, the effect of laser beam nonuniformity on shockfront or ablation pressure uniformity, the smoothing of shockfront and pressure profiles in high-Z coated and high-Z doped targets, and so on, are the various experimental studies conducted. We have tried to study X-ray driven ablation in aluminum and plastic targets using gold and copper as X-ray producing targets. Uniform pressure of about 0.1 Mbar has been generated over an area of 4 mm2

A high-power Nd3+:glass laser system has been constructed and tested. This system consists of a master oscillator, a four-pass amplifier for preamplification, and five-stage amplifiers. The system has been demonstrated in excess of 80 J (2 TW) at 40-ps pulse duration. Final laser beam quality was quite good due to the compensation of the polarization distortion in the four-pass preamplifier, the minimization of the diffraction effect by the image relaying, and the elimination of high spatial frequency components by the spatial filtering. This enables us to obtain high laser output power without any severe spatial spiking effects. Gains and spatial profiles of output pulses were measured after each amplifier stage.

A method is proposed to evaluate the power brightness of an intense pulsed ion beam by using a Thomson parabola spectrometer (TPS). In the method, the time-dependent power brightness of each ion species can be determined independently from the density profile of ion tracks. The method is successfully utilized to evaluate the power brightness of ion beams produced in point pinch diode. The brightness of highly ionized carbons of 660 keV and oxygens of 880 keV, and singly ionized molecular ions of 400 keV, are evaluated independently. The total brightness is evaluated to be 3.2 GW/cm2/sr for highly ionized ions, and 1.9 GW/cm2/sr for molecular ions.

Results of an experimental study of a coaxial exciplex lamp pumped by glow discharge are presented. An average power of radiation in the wavelength region below 250 nm and as high as about 130 W has been achieved. Efficiency of the excilamp operation based on input power of 14% was demonstrated. The possibility of applications of this excilamp is discussed.