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The electron-beam-pumped ArF laser is a laser technology capable of providing very high lasing energies at the shortest wavelength (λ = 193 nm) among the rare gas halide lasers and therefore has the potential to be a superior driver for inertial fusion. The electron kinetics are rigorously treated by numerically solving the steady-state, spatially averaged electron Boltzmann equation in Ar-F2 gas. The e-beam energy deposition and collisional reaction rates with electrons are calculated from the electron energy distribution function for a wide range of e-beam deposition powers (Pbeam =10 kW/cm3 –3 MW/cm3) and fluorine concentrations (xF2 = 0.01 – 10%). The rates are reduced to a set of coefficients that are fitted with analytical formulas as a function of two universal parameters: Pbeam/p and xF2 , where p is the gas pressure. It is found that in the regime of high e-beam power deposition, the fluorine molecules are rapidly destroyed through dissociative attachment and neutral dissociation. The loss of F2 over the duration of the beam is proportional to the e-beam energy deposition per unit volume, ebeam, and follows ΔnF2 (cm-3) ≅ 4 x 1017 દbeam(J /cm3, in agreement with experimental data. The fluorine molecule conversion to other fluorine species, including atomic fluorine, is shown to have a very small effect on the index of refraction even at percent level concentrations. [ABSTRACT FROM AUTHOR]

Carbon dioxide is the most important greenhouse gas contributing to global warming. To help mitigate increasing CO2 concentrations, we investigate a method of carbon dioxide reduction using high-power electron beams, which can be used on an industrial scale. A series of experiments are conducted in which the reduction of CO2 is measured for different gas compositions and power deposition rates. An electron beam deposition model is applied to compute reduction rates of CO2 and energy cost for breaking a CO2 molecule in flue gas and pure carbon dioxide at atmospheric pressure. For flue gas consisting of 82% N2, 6% O2, and 12% CO2, the calculated energy cost is 85 eV per molecule. In order to dissociate 50% of the CO2 molecules, beam energy density deposition on the order of 20 J/cm³ is required. Electron beam irradiation of 12.6 liter gas volume containing 90% CO2 and 10% CH4 at beam energy density deposition of 4.2 J/cm³, accumulated over 43 shots in a 20 min interval, reduced the CO2 concentration to 78%. Analogous experiments with a gas mixture containing 11.5% CO2, 11.5% CH4, and balance of Ar, reduced the CO2 concentration to below 11% with energy deposition 0.71 J/cm³, accumulated over 10 shots in a 5 min interval. The experimental data and the theoretical predictions of CO2 reduction using pulsed electron beams are in agreement within the experimental error. Other techniques to enhance the removal of CO2 with pulsed electron beams are also explored, yielding new possible avenues of research. [ABSTRACT FROM AUTHOR]

A theoretical study complemented with published experimental data of proton acceleration from sub-micron (thickness < 1 µm) foils irradiated by ultra-high contrast (>1010) short pulse lasers is presented. The underlying physics issues pertinent to proton acceleration are addressed using two-dimensional particle-in-cell simulations. For laser energy ε ≤ 4 J (intensity I ≤ 5 x 1020 W/cm²), simulation predictions agree with experimental data, both exhibiting scaling superior to Target Normal Sheath Acceleration's model. Anomalous behavior was observed for ε > 4 J (I > 5 x 1020 W/cm²), for which the measured maximum proton energies were much lower than predicted by scaling and these simulations. This unexpected behavior could not be explained within the frame of the model, and we conjecture that pre-pulses preceding the main pulse by picoseconds may be responsible. If technological issues can be resolved, energetic proton beams could be generated for a wide range of applications such as nuclear physics, radiography, and medical science. [ABSTRACT FROM AUTHOR]

The Ar–Xe infrared laser has been investigated in several series of experiments carried out on the Naval Research Laboratory’s Electra generator. Our primary goals were to optimize the efficiency of the laser (within Electra’s capabilities) and to gain understanding of the main physical processes underlying the laser’s output as a function of controllable parameters such as Xe fraction, power deposition, and gas pressure. We find that the intrinsic efficiency maximizes at ∼3% at a total pressure of 2.5 atm, Xe fraction of 1%, and electron beam power deposition density of 50–100 kW cm-3. We deployed an interferometer to measure the electron density during lasing; the ionization fractions of 10-5–10-4 that it detected well exceed previous theoretical estimates. Some trends in the data as a function of beam power and xenon fraction are not fully understood. The as-yet incomplete picture of Ar–Xe laser physics is likely traceable in large part to significant uncertainties still present in many important rates influencing the atomic and molecular kinetics. [ABSTRACT FROM AUTHOR]

The inhomogeneous electron Boltzmann equation is solved for an Ar-Hg positive column direct current glow discharge with properties similar to the standard fluorescent lamp. The inhomogeneity arises from the ambipolar potential and requires the inclusion of the spatial gradient term in the Boltzmann equation. The electron kinetics is coupled to a collisional-radiative equilibrium model for various states of Ar and Hg subject to a reaction set with electron and heavy particle collisions. The axial electric field and space-charge potential are solved self-consistently. The calculated electron distribution function satisfies neither the local nor nonlocal approaches, but rather is found to be a function of both the electron energy and radial position. The radial dependence produces an energy flow from one part of the discharge to another, which results in nonuniform ultraviolet radiative power. Results are given for global properties of the discharge such as power per unit length and axial electric field, as well as spatially averaged quantities (densities, electron and gas temperatures, and emission powers) as a function of the wall temperature and the current. Extensive comparisons are presented with experimental data and previous homogeneous Boltzmann models of the discharge. The optimum current and fill pressures are determined and the general trends of varying the input parameters are established. There is general agreement between the present model and data, except that the calculated average electron density is larger than the measured values. [ABSTRACT FROM AUTHOR]

Calculations for electron deposition in electron beam generated KrF laser at atmospheric pressure have been performed. The impact of the Ar/Kr/F[sub 2] gas mixture on the electron energy distribution function, electron density, and mean energy, energy per electron-ion pair, attachment, dissociation, excitation, and ionization rates have been investigated. The F[sub 2] abundance controls the low energy (... 9 eV) component of the distribution function, while both the fluorine and krypton mole fraction affect the distribution in the midenergy domain (9 to ∼ 25 eV). Consequently, the F[sub 2] attachment rate coefficient varies with the F[sub 2] mole fraction (χF[sub 2]) such that the electron density scales as 1/χ[sup 0.7][sub F][sub 2]. The rate coefficient for direct dissociation of F[sub 2] is smaller than for attachment but the former contributes more to the total power dissipation (∼ 8% at χ[sub F][sub 2] = 0.01). The excitation-to-ionization ratio for Kr is not constant, as generally assumed, but increases by a factor of two with a decrease in either the Kr or F[sub 2] abundance. Combining the former and present investigations leads to a set of fitting formulas to be used in beam kinetics codes for various collision rates as a function of both the electron beam power density and the composition. [ABSTRACT FROM AUTHOR]

The electron deposition in an Ar-Kr-F[sub 2] mixture, based on a solution of the electron Boltzmann equation, is presented. The model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure. Sets of cross sections for Ar, Kr, and F[sub 2] have been compiled. Calculations have been performed to determine the electron energy distribution function, energy per electron-ion pair and the ionization and excitation rates. It is found that the inclusion of inner shell ionization and the subsequent Auger emission are essential for matching known results on both the energy per electron-ion pair W[sub ei] and the stopping power in pure Ar or Kr target gases. For the chosen Ar-Kr-F[sub 2] mixture, W[sub ei] is calculated to be 24.6 eV. The excitation-to-ionization ratio is calculated to be 0.38 for Ar and 0.54 for Kr at low input power density P[sub beam] ( 1 kW/cm[sup 3]). Both ratios increase with P[sub beam], particularly for Kr which attains 0.8 at 1 MW/cm[sup 3]. The dependency on P[sub beam] and the excitation efficiency for Kr is significantly higher than previously assumed in KrF* kinetic models. Results are also compared with the continuous slowing down approximation to demonstrate that this approach is limited to the regime of low power deposition. [ABSTRACT FROM AUTHOR]

A reactor is proposed for plasma-enhanced chemical-vapor deposition of silicon carbide (SiC) at low pressure (∼few Torr). The inductively coupled plasma lies upstream of the growth substrate and serves to dissociate the precursor silane/propane/hydrogen inlet gas. Unlike existing reactors, the design offers the potential for separate control of the temperature in the dissociation region and at the growth substrate. The geometrical parameters and flow conditions appropriate for SiC growth are analyzed with a one-dimensional flow simulation model which includes approximations for lateral diffusive losses to cold walls as well as deposition to the substrate. Twenty-one neutral species and 24 ions are followed with 179 reactions. At 3 Torr, 10 W/cm3, and 300 cm/s inlet flow velocity, the model predicts a growth rate of ∼3 μm/h downstream from the plasma. Negligible ion density exists over the substrate as long as the silane density is sufficiently large due to a feedback process between Si[sup +] and SiH[sub 4]. Besides heating the gas, the plasma is an efficient source of radical H atoms, which in turn control the abundance of some hydrocarbon species over the substrate. C[sub 2]H[sub 2] is the dominant contributor to the C-bearing flux onto the substrate and the Si atom, which forms by electron reactions, is the most important Si-bearing species. Finally, a sensitive transition in deposition rate is found for the C-bearing species as the power increases from 5 to 10 W/cm3. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]