The acceleration of electrons in a laser plasma at the densities below the critical one is investigated by a particle simulation. It is shown that the stabilization of parametric instability and limitation of the energies of the accelerated electrons take place. The structure of the plasma electron distribution function is examined.

A fundamental problem for the realization of laser fusion through the implosion of a spherical target is Kidder's E−1/6 law, where E is the energy needed for ignition, proportional to the 6th power of the ratio R/R0, where R0 and R are the initial and final implosion radii, respectively. This law implies that the ignition energy is very sensitive to the ratio R0/R, or vice versa, the ratio R0/R is very insensitive to the energy input, with R0/R limited by the Rayleigh–Taylor instability. According to still classified data of the Centurion–Halite experiment at the Nevada Test Site, ignition would require an energy of ${\rm E}\simeq 50\,{\rm MJ}$, 25 times larger than the 2 MJ laser at the National Ignition Facility (NIF) reported in the New York Times. This means that even a tenfold increase from 2 to 20 MJ would only decrease the R/R0 ratio by an insignificant factor of 10−1/6 ≃ 0.7. To overcome this problem, it is proposed that the spherical target is replaced with a hollowed-out, rapidly rotating, cm-size ferromagnetic target, accelerated by a rotating traveling magnetic wave to a rotational velocity of ~1 km/s, at the limit of its tensile strength. In a rotating reference system, the general theory of relativity predicts the occurrence of negative gravitational field masses in the center of rotation, with their source located in the Coriolis force field. The density of this negative gravitational field mass can be larger than the magnitude of the positive mass density of a neutron star. The repulsive gravitational force causes the centrifugal force. For a magnetized plasma placed in the rapidly spinning, hollowed-out target chamber, this repulsive force can be balanced by the magnetic force generated by thermomagnetic currents of the Nernst effect. Such a configuration does not suffer from the Rayleigh–Taylor instability, but becomes a small magnetohydrodynamic generator, amplifying the magnetic field to values about equal to those of the Nernst effect, axially confining the plasma. By placing the spinning target in the center of a lithium vortex, the fusion neutrons absorbed in the vortex can breed tritium, and at the same time remove heat from the target chamber to sustain the Nernst effect. A hot spot is thereby produced in the target chamber, which launches a thermonuclear burn wave into a cylindrical deuterium–tritium configuration. With the stability of a rapidly rotating target greatly increased, and the range of 10 MeV electrons in the wall of the cm-size ferromagnetic target, an intense 10 MeV relativistic electron beam drawn from a 10 MJ Marx generator should be sufficient to implode the target for thermonuclear ignition.

The dynamics of low entropy weak shock waves induced by heavy ion beams in solid targets was investigated by means of a schlieren technique. The targets consist of a metallic absorber for the beam energy deposition followed by a plexiglass block for optical observations. Multiple waves propagating with supersonic velocities at 15 kbar pressures were observed in the plexiglass, for pressures of up to 70 kbar numerically calculated in the absorbers. Pressures in the megabar ranges are predicted for a near future beam upgrade, enabling studies of phase transition to metallic states of H, Kr, and Xe.

When a heavy ion beam passes through a plasma in reactor chamber, it scatters some plasma electrons in the direction perpendicular to that of beam propagation. The presence of such electrons causes an instability to deflect the beam from the target pellet. The instability is analyzed by coupled equations for density and temperature for the electrons, and numerical results are given.

Far-field images produced using different random phase plates on a pulsed laser beam focused with variousf/numbers were recorded by a charge-coupled device (CCD) camera and then analyzed. Envelope spot sizes agree with diffraction theory while mean sizes of the pattern structures have been found to be larger than the diffraction limit. The probability density distribution of intensity in the focal plane is not the expected exponential. A central symmetry of the pattern has also been seen after suitably aperturing the beam. Some consequences for the use of powerful RPP-treated laser beams in laser-plasma interactions are discussed.

A computer model has been developed and benchmarked for the nuclear-pumped atomic carbon laser. Experiments have been performed with the atomic carbon laser and with the radiolysis of CO2 as a benchmark for the model. The results of the CO2 radiolysis are described.

We investigated several examples of ion beam targets that utilize the energy efficiency of direct drive while optimizing on the symmetry requirements. Heavy-ion beams of charge state Z ≥ 3 at 5–10 GeV have ≲15–20 m bending radii with 3.5-T fields. Beams like these could be used with targets involving direct drive. Control of asymmetries in direct-drive ion beam targets depends on control of the effects of residual target asymmetries after an appropriate illumination scheme has been adopted. In this paper, we outline results of our investigations into ion beam target concepts in which the effects of residual asymmetries are ameliorated. The beams are placed according to our axially symmetric Gaussian-quadrature illumination scheme (Mark 1986). The targets survive the effects of residual asymmetries in our recent 2-D hydrodynamic simulations. We also briefly discuss the additional positive effects of polarized DT fuel on ion beam targets.

To predict the gain in a lasing transition in ions of a laser-produced plasma, it is essential to calculate the amount of the reabsorption of radiation emitted in the transition from the lower laser level to the ground state. An important quantity influencing the reabsorption is the plasma geometry as resulting from the design of the laser and target system. Modeling a nonaxially symmetrical geometry of the plasma arising from a target irradiated by line-focused laser beams, we consider the plasma in the form of a longitudinally cut-out circular cylinder, with central angle ø, and the length of the plasma much larger than its transversal extension. Accounting for the effect of resonance line trapping via the escape probability approach, and taking the absorption profile in the line center approximation, an explicit formula for the photon escape probability depending on the radial and angular coordinates of an interior point in the plasma is derived. This function is averaged over the angular variable to obtain an only radially varying mean escape probability.

A theoretical and experimental study of line broadening and merging is presented and suggested for diagnosis of high density laser plasmas. For densities larger than 1022 cm−3 the hydrogenlike sequence is reduced to four lines for the emitter ion with ZE = 9. The perturbation effects on the latter come mainly from the interaction with plasma ions and electrons (Stark effect, multipolar interactions, ionization by tunnel effect, polarization line shift …).

We present the results of the theoretical studies of the plasma heating in the flows which converge toward the axis of cylindrical cavity. We show that as a result of the shock wave reflection from the axis, the narrow hot filament is formed. This phenomenon is important for the interpretation of the dynamic processes in the electric discharges used for X-ray generation. We notice that the plasma parameters which can be of interest for inertial confinement fusion (ICF) can be reached in such the processes.

The main purpose of this work is to describe the construction and operation of the low energy accelerator with energy in the range from (zero to 100 KeV). This accelerator includes an ion source of the cold cathode Penning type (with pierce geometry for ion beam extraction), an accelerating tube (with 8 electrodes) and Faraday cup (FC) for measuring ion current. A vacuum system which gives vacuum of the order 3.0 × 10−8 Torr is used. A palladium tube is used to supply the source with pure hydrogen atoms. It was possible to operate this accelerator with an energy 50 KeV at minimum hydrogen pressure, 6.3 × 10−6 Torr. The total resistance applied between the accelerating electrodes RT = 31.5 MΩ. These data include the influence of the pressure in the accelerating tube, the magnetic field of the ion source, the extraction potential and the accelerating potential on the collector ion current. It was possible to accelerate protons with an energy 50 KeV with current about 100 μA at pressure 6.3 × 10−6 Torr, the source magnetic field = 110 G (IB = 2 A), the arc current = 0.4 A and the extraction potential = 10 KV.

The spectra of laser-produced plasmas of various materials of Z>70 have been interpreted as spin-orbit-split arrays of the 3d – 4f and 3d – 5f transitions for Ni-like to Ge-like ions. The excellent agreement between the model and the experiments indicated the possibility of their use for plasma diagnostics. First results from targets of Gold alloyed with Aluminium give an alternative diagnostic.

In doing research on the turbulent mixing (TM) of two gases different in density, it is of great interest to study experimentally the 3D density distribution pattern of chemically nonreactive gases in the TM zone. For this purpose, noncontact and, particularly, optical techniques to obtain experimental data may be attractive. This article discusses the possibility of using pulsed laser interferometry in this application. Based on this technique, the experiment should result in the mixture density distribution integrated along the light path. Requirements for high-quality interference patterns have been analyzed in application to typical experimental conditions, to show that they may be produced with specific restrictions set on the mixture constitution. Generally, the TM zone has no symmetry. Therefore, the problem of reconstructing 3D density distributions (TDD) of gases can be solved by sufficiently providing many TM zone integral projections (or aspects). It is technically difficult and expensive to achieve this large number of aspects (N> 10). Therefore, it is essential that a reconstruction method be selected to allow the solution of the problem with the least possible number of aspects. Given that the experiment data are incomplete, the reconstruction methods that are based on the concept of maximum data entropy did well. Information a priori about the solution to be sought for an isobaric gas mixture is that its each constituent has invariable density. Thus, a functional data entropy can be defined that is similar to Fermi gas in statistical physics. An algorithm has been suggested for reconstruction as a modified maximum-bounded entropy procedure (Bashurin et al. 1995). This makes reasonable good reconstruction achievable even with as few aspects as N = 4. Experiments on the study of TM of a propane jet in air using a four-aspects laser interferometer were provided and reconstruction of propane concentration distribution was conducted. The results allow determination of the TM zone spectral characteristics.

A vertical dispersion variant of the Johann spectrometer has been used to record the highresolution X-ray spectra of the chlorine He-like resonance line group emitted from lowradiance plasma. The emission profiles were measured at two observation angles and decomposed into single spectral lines by using a fit based on the Levenberg-Marquardt algorithm. The results of computerized analysis of the one-dimensional (1-D) spatially resolved spectra were used to evaluate the distribution of the main plasma parameters. The electron temperature gradient 7.5·104 eV cm-1 was computed by modeling the measured spectra with the collisional-radiative package RATION. The blowoff maximum velocities 4.2–6.1·107 cm s-1 and the velocity gradients 0.9–1.6·109 s-1 were determined from the Doppler shifts of individual spectral lines within their different spatial extent.

Temporal evolution of X-ray spectra of lead plasma produced by a CO2 laser pulse with energy of 100 J and a duration of 15 ns has been measured using a six-channel X-ray polychromator. The polychromator registered the radiation intensity in the range from 180 to 1850 eV. Plasma temperature was determined by comparison of measured results with radiation spectra obtained by numerical simulation. The values of electron temperature are in good agreement with results of hydro simulations.

Smoothing of laser-plasma interaction by ISI, RPP, SSD, etc. was mainly directed to overcome lateral nonuniformity of irradiation. While these problems are in no way less important, we derived numerically the model of the Laue rippling and hydrorelaxation model for explanation of the measured temporal pulsation in the 10- to 40-ps range and how the smoothing schemes suppress these pulsations. The partial standing wave fields of the normally coherent laser-irradiated plasma corona is then suppressed by smoothing and conclusion for tests for this model, e.g., by the “question mark experiment” is given. The result provides a physics solution of the laser interaction problem for direct-drive inertial fusion energy