Tabletop X-ray Lasers

Details of schemes for two tabletop size x‐ray lasers that require a high‐intensity short‐pulse driving laser are discussed. The first is based on rapid recombination following optical‐field ionization. Analytical and numerical calculations of the output properties are presented. Propagation in the confocal geometry is discussed and a solution for x‐ray lasing in Li‐like N at 247 Å is described. Since the calculated gain coefficient depends strongly on the electron temperature, the methods of calculating electron heating following field ionization are discussed. Recent experiments aimed at demonstrating lasing in H‐like Li at 135 Å are discussed along with modeling results. The second x‐ray laser scheme is based on the population inversion obtained during inner‐shell photoionization by hard x rays. This approach has significantly higher‐energy requirements, but lasing occurs at very short wavelengths (λ ≤ 15 Å). Experiments that are possible with existing lasers are discussed

Adsorption of para-Hydrogen on Krypton pre-plated graphite

Adsorption of para-Hydrogen on the surface of graphite pre-plated with a single layer of atomic krypton is studied thoretically by means of Path Integral Ground State Monte Carlo simulations. We compute energetics and density profiles of para-hydrogen, and determine the structure of the adsorbed film for various coverages. Results show that there are two thermodynamically stable monolayer phases of para-hydrogen, both solid. One is commensurate with the krypton layer, the other is incommensurate. No evidence is seen of a thermodynamically stable liquid phase, at zero temperature. These results are qualitatively similar to what is seen for for para-hydrogen on bare graphite. Quantum exchanges of hydrogen molecules are suppressed in this system.Comment: 12 pages, 6 figures, to appear in the proceedings of "Advances in Computational Many-Body Physics", Banff, Alberta (Canada), January 13-16 200

Lawrence Livermore National Laboratory's activities to achieve ignition by x-ray drive on the National Ignition Facility

The National Ignition Facility (NIF) is a MJ-class glass laser-based facility funded by the Department of Energy which has achieving thermonuclear ignition and moderate gain as one of its main objectives. In the summer of 1998, the project is about 40% complete, and design and construction is on schedule and on cost. The NIF will start firing onto targets in 2001, and will achieve full energy in 2004. The Lawrence Livermore National Laboratory (LLNL), together with the Los Alamos National Laboratory (LANL) have the main responsibility for achieving x-ray driven ignition on the NIF. In the 1990�s, a comprehensive series of experiments on Nova at LLNL, followed by recent experiments on the Omega laser at the University of Rochester, demonstrated confidence in understanding the physics of x-ray drive implosions. The same physics at equivalent scales is used in calculations to predict target performance on the NIF, giving credence to calculations of ignition on the NIF. An integrated program of work in preparing the NIF for x-ray driven ignition in about 2007, and the key issues being addressed on the current ICF facilities [(Nova, Omega, Z at Sandia National Laboratory (SNL), and NIKE at the Naval Research Laboratory (NRL)] are described

Target experimental area and systems of the U.S. National Ignition Facility

One of the major goals of the US National Ignition Facility is the demonstration of laser driven fusion ignition and burn of targets by inertial confinement and provide capability for a wide variety of high energy density physics experiments. The NIF target area houses the optical systems required to focus the 192 beamlets to a target precisely positioned at the center of the 10 meter diameter, 10-cm thick aluminum target chamber. The chamber serves as mounting surface for the 48 final optics assemblies, the target alignment and positioning equipment, and the target diagnostics. The internal surfaces of the chamber are protected by louvered steel beam dumps. The target area also provides the necessary shielding against target emission and environmental protection equipment. Despite its complexity, the design provides the flexibility to accommodate the needs of the various NIF user groups, such as direct and indirect drive irradiation geometries, modular final optics design, capability to handle cryogenic targets, and easily re-configurable diagnostic instruments. Efficient target area operations are ensured by using line-replaceable designs for systems requiring frequent inspection, maintenance and reconfiguration, such as the final optics, debris shields, phase plates and the diagnostic instruments. A precision diagnostic instrument manipulator (DIMS) allows fast removal and precise repositioning of diagnostic instruments. In addition the authors describe several activities to enhance the target chamber availability, such as the target debris mitigation, the use of standard experimental configurations and the development of smart shot operations planning tools

Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

Hydrodynamic instabilities can cause capsule defects and other perturbations to grow and degrade implosion performance in ignition experiments at the National Ignition Facility (NIF). Here, we show the first experimental demonstration that a strong unsupported first shock in indirect drive implosions at the NIF reduces ablation front instability growth leading to a 3 to 10 times higher yield with fuel ρR > 1  g/cm[superscript 2]. This work shows the importance of ablation front instability growth during the National Ignition Campaign and may provide a path to improved performance at the high compression necessary for ignition

Characterizing high energy spectra of NIF ignition hohlraums using a differentially filtered high energy multi-pinhole X-ray imager

Understanding hot electron distributions generated inside hohlraums is important to the ignition campaign for controlling implosion symmetry and sources of preheat. While direct imaging of hot electrons is difficult, their spatial distribution and spectrum can be deduced by detecting high energy x-rays generated as they interact with the target materials. We used an array of 18 pinholes, with four independent filter combinations, to image entire hohlraums with a magnification of 0.87x during the hohlraum energetics campaign on NIF. Comparing our results with hohlraum simulations indicates that the characteristic 30 keV hot electrons are mainly generated from backscattered laser plasma interactions rather than from hohlraum hydrodynamics