A mechanism of trapping and entrainment of electromagnetic (EM) field pulses into supercritical regions of an inhomogeneous plasma by ion-acoustic waves is considered.

A method of probing beam refraction is suggested for the investigation of laserproduced plasma with high density gradients. The refraction angle α of a probing ray as a function of ray impact parameter p is used as input data. Different experimental realizations of α(p) measurements are considered. Results from laser produced plasma interferograms processed with phase shift and refractometry methods are compared.

A numerical model for opacity calculations by using a family of analytical potentials for each configuration in the plasma is presented. The obtained numerical opacity results with this model are compared with those obtained by using a self-consistent potential model.

Recent progress in research on Light Ion Beams-Inertial Confinement Fusion (LIB-ICF) at ILE, Osaka University is summarized. We report on pulsed power compression using PEOS, a super high voltage source, on diode physics, on beam trajectory control for focusing, on beam-target interactions and on a conceptual reactor design (Rokko I) in this article.

We present a Ramsey technique using high-order harmonics for high-resolution atomic spectroscopy in the extreme ultraviolet. Pairs of time-delayed and phase-coherent harmonic pulses generated by the interaction of ultrashort and intense laser pulses with a noble gas are used to study excited states of krypton.

We present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

The results of formation of elongated krypton/helium plasma channels are presented. Two laser pulses were used: one to produce plasma channels and the second one for conversion to soft X rays. The soft X-ray radiation was in turn used for backlighting the channels and their visualization. The study of their formation and uniformity was performed using a combination of soft X-ray shadowgraphy and pinhole camera imaging. The plasma channels, with various lengths and various densities, were visualized and the results of their characterization are presented. Using moderate laser pulse energy quite uniform channels, up to 9 mm in length, were demonstrated.

As the strong thermal effect in the surface, intense pulsed ion beam (IPIB) has been extensively used in material surface modification. The ablation is an important part in the interaction process between IPIB and material. In order to investigate the ablation mechanism, combined with IPIB dynamic energy spectrum and infrared imaging diagnostic results, a two-dimensional axisymmetric heat conduction model considering the effect of ablated material was constructed to describe the ablation process and calculate the lost mass of the targets. The influences of beam parameters and ablated matter on the ablation rate were discussed. The experimental and simulative results of ablation threshold and mass were compared.

The effect of laser intensity distribution along the line focus on the uniformity of the line-shaped plasmas produced is investigated with time-integrated and time-resolved soft X-ray and optical diagnostics. Evident plasma condition nonuniformities along the line focus resulting from nonuniform laser intensity distributions have been observed with a conventional simple line-focusing technique. With a new line-focusing technique producing a uniform laser illumination, a uniform, line-shaped plasma can be obtained. It is also found that nonuniformities under uniform laser illumination occur mostly during laser heating. The line-shaped uniform laser plasma can be used as a large, uniform X-ray source besides its importance in X-ray laser demonstration and amplification. As an application of such line-shaped plasmas as X-ray sources, the no-overcoat 5F X-ray film is calibrated for the first time by a new method in the soft X-ray range from 10–80 A.

A new inverse Compton scattering scheme for production of high-energy Gamma-ray sources is proposed in which a Giga-electronvolt (GeV) electron beam is injected into a thermal hohlraum. It is found that by increasing the hohlraum background temperature, the scattered photons experience kinematic pileup, resulting in more monochromatic spectrum and smaller scattering angle. When a relativistic electron beam with energy 1 GeV and charge 10nC is injected into a 0.5 keV hohlraum, 80% of the scattered photons have energy above 0.5 GeV.

The main tool for the laser plasma work at MPQ (Max-Planck-Institut für Quantenoptik) is the ASTERIX iodine laser delivering 300 J/300 ps pulses at 1·3 m, operational also at 2ω and 3ω. A fifth 30-cm diameter am lifier is under construction to increase the pulse energy up to 2 kJ.

Soft X-ray radiation emitted by laser plasmas and its influence on energy transport and hydrodynamics is studied. Time and space resolved spectroscopic measurements of soft X-radiation from a variety of targets are compared with analytical models and computer results. Planck radiation is produced in gold cavities to study radiation hydrodynamics. Theoretical work comprises shock waves in solids, the electronic structure of very high density matter, radiation pumped X-ray laser and development of the appropriate computer codes.

Estimates indicate that dense plasmas with temperatures of several ten keV can be produced with the heavy ion accelerator now under construction at GSI-Darmstadt. Experiments are being prepared to be started in 1991. Measurements at the present UNILAC-accelerator confirm the theoretical prediction that the energy loss of heavy ions in a plasma is much higher than in cold matter.

Free-electron lasers exploiting media with periodically modulated refractive indices are studied. The regime of large modulation is considered, and the conditions of its realization are discussed. Two types of media with periodically modulated refractive indices are analyzed: a gas-plasma medium with a periodically varying degree of ionization and a superlattice-like medium. The gain, saturation field, and efficiency of these free-electron lasers are found. For any given frequency, the gain is optimized with respect to the choice of electron energy, direction of motion, and other parameters. Its relationship with other types of free-electron lasers (e.g., the Cherenkov laser) is discussed.

Tritium self-heats at a rate of 97 W/mole because of its β activity. This energy drives preferential sublimation of solid T2 or DT from regions where a layer is thicker and warmer to regions where the layer is thinner and colder. A frozen tritium layer inside an isothermal container approaches isotropy exponentially with a time constant as short as 14.4 minutes. Targets Isotropized by Radioactively Induced Sublimation (IRIS) and sized for an ICF reactor demonstrate high gain and offer real fabrication advantages.

An effective theory of laser–plasma-based particle acceleration is presented. Here we treated the plasma as a continuous medium with an index of refraction nm in which a single electron propagates. Because of the simplicity of this model, we did not perform particle-in-cell (PIC) simulations in order to study the properties of the electron acceleration. We studied the properties of the electron motion due to the Lorentz force and the relativistic equations of motion were numerically solved and analyzed. We compared our results with PIC simulations and experimental data.

Energetic electrons, with energy from many tens to several hundred keV can be generated in laser produced plasmas by such laser plasma instabilities as the 2ωp instability, which occurs at the quarter critical density. It is important to know not only how these are produced, but also how they are transported and deposit their energy in the interior and whether they preheat the fuel. We introduce the velocity dependent Krook approach to this problem, and compare it to other approaches that have appeared in the literature as regards accuracy and economy of incorporating in a fluid simulation. This velocity dependent Krook technique is reasonably accurate and reasonably simple and economical to incorporate into a fluid simulation.

A density-matrix approach is under development for the investigation of the angular distribution and polarization of atomic radiative emissions in crossed quasi-static electric and magnetic fields. Particular interest has centered on applications to spectroscopic observations in the intense fields of the high-power light-ion inertial fusion device PBFA II at Sandia National Laboratories, and to magnetic field measurements in tokamak plasmas. Noteworthy features of our general density-matrix analysis include allowances for the mixing of both the bound and continuum field-free atomic eigenstates in an arbitrary arrangement of electric and magnetic fields, and for the possible coherent excitation of the nearly degenerate field-dependent atomic substates that produce the overlapping Stark-Zeeman components. The influence of directed collisional excitation may also be taken into account. From the angular-momentum selection rules, specific results have been obtained for observation of polarized radiative emissions in the direction of the magnetic field.

The Heavy-Ion Fusion Systems Assessment project is nearing completion of a two-year effort. The resulting system modelwill be used to set directions for future target design work.

Major uncertainties in target design were studied using thecost of electricity as a figure of merit. Net electric power was fixed at 1000 MW to eliminate large effects due to economies of scale. The system is relatively insensitive to target gain, factors of three changes in gain resulting in 8 to 12% changes in electricity cost. Possible increased peak power requirements pose only a small cost risk, but require many more beamlets for transport. A shortening ofthe required ion range causes both cost and beamlet difficulties. A factor of 4 decrease in the required range at a fixed driver energy increases electricity cost by 44% and raises the number of beamlets to 240. Finally, the heavy ion fusion system can accommodate large increases in target costs. Thus, to address the major uncertainties, target design should concentrate on requirements for ion range andpeak driver power.

In this paper, a study on a fusion reactor core is presented in heavy-ion inertial fusion (HIF), including the heavy-ion beam (HIB) transport in a fusion reactor, an HIB interaction with a background gas, the reactor cavity gas dynamics, the reactor gas backflow to the beam lines, and an HIB fusion reactor design. The HIB has remarkable preferable features to release the fusion energy in inertial fusion: in particle accelerators HIBs are generated with a high driver efficiency of about 30–40%, and the HIB ions deposit their energy inside of materials. Therefore, a requirement for the fusion target energy gain is relatively low, that would be ~50 to operate an HIF fusion reactor with a standard energy output of 1 GW of electricity. In a fusion reactor, the HIB charge neutralization is needed for a ballistic HIB transport. Multiple mechanical shutters would be installed at each HIB port at the reactor wall to stop the blast waves and the chamber gas backflow, so that the accelerator final elements would be protected from the reactor gas contaminant. The essential fusion reactor components are discussed in this paper.

Flux waveforms of aluminum cluster beams supplied from a laser-ablation cluster source were precisely investigated under various source conditions such as background pressure, ablation laser intensity, and nozzle structure. A time-of-flight mass spectroscopy revealed that aluminum clusters with sizes up to 200 were generated and the amount of the clusters could be maximized by choosing a proper background pressure (~2 MPa) and an ablation laser fluence (~40 mJ/cm2). Flux waveforms of clusters having specific sizes were carefully reconstructed from the observed mass spectra. It is found that the pulse widths of the aluminum cluster beams were typically about 100 µs and much smaller than that of the monoatomic aluminum beam, indicating that the cluster formation was limited in a relatively small volume in the laser-ablated vapor. Introducing a conical nozzle having a large open angle was also found to enhance the cluster beam velocity and reduce its pulse width. A velocity measurement of particles in the cluster beam was conducted to examine the velocity spread of the supplied clusters. We found that the aluminum clusters were continuously released from the source for about 100 µs and this release time mainly determined the pulse width of the cluster beam, suggesting that controlling the behavior of an ablated vapor plume in the waiting room of the cluster source holds the key to drastically improving the cluster beam flux.