Charles B. Thorsness

Dehydroxylation of phosphate laser glass

Rates of dehydroxylation of two Nd-doped metaphosphate laser glasses (LG-770 and LHG-8) are measured and modeled. Glass melts ranging in size from 100 g to 2.8 kg were bubbled with O2 containing various H2O partial pressures (PH(subscript 2O)) and with O2/Cl2 mixtures at temperatures ranging from 925 - 1300 degree(s)C. The OH content in the glass was measured by monitoring the OH absorption at 3.333 micrometers at various bubbling times. The OH removal by inert gas bubbling (e.g. O2 bubbling) is governed by the transport (diffusion) of OH to the glass liquid/vapor interface and by the chemical equilibrium between OH at the surface and H2O in the gas phase. The equilibrium OH content in glass melts bubbled with O2 containing different PH(subscript 2O) varies as PH(subscript 2O)1/2.

Phosphate laser glass for NIF: production status, slab selection, and recent technical advances

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is a stadium-sized high-energy (1.8 megajoule) / high-peak power (500 terawatt) laser system, which will utilize over 3000 meter-size Nd-doped metaphosphate glasses as its gain media. The current production status, the selection criteria of individual slabs for specific beam line locations, and some recent technical advances are reviewed. The glass blanks are manufactured by a novel continuous glass melting process, and the finished slabs are then prepared by epoxy bonding a Cu-doped phosphate glass edge cladding and by advanced finishing techniques. To date, nearly 3400 slab equivalents have been melted, 2600 have been rough-cut to blanks, 1200 have been finished, and 144 have been installed in NIF. A set of selection rules, which are designed to optimize laser performance (e.g., maintain gain balance between beam lines and minimize beam walkoff) and to maximize glass lifetime with respect to Pt damage site growth, have been established for assigning individual slabs to specific beam line locations. Recent technical advances for amplifier slab production, which include: 1) minimizing surface pitting (hazing) after final finishing; 2) minimizing humidity-induced surface degradation (weathering) upon storage and use; and 3) preventing mounting-induced surface fractures upon installation, have contributed in improving the laser glass quality.

Hoe Creek II Revisited: Boundaries of the Gasification Zone

Abstract Lawrence Livermore Laboratory has completed an exploratory drilling program at the site of the Hoe Creek II Field Experiment on in situ coal gasification. We have used the results to further define the boundaries of the gasification zone. The gasification zone was 12 to 16 m wide and extended at least 7.6 m behind the injection well and 18 m toward the production well. All the coal within 2.9 m of the injection well was gasified despite an override condition that existed almost from the start of forward-combustion gasification. Cavity-spreading mechanisms that do not depend on the product flow paths being at the bottom of the seam are suggested. Natural convection may drive these mechanisms. For these mechanisms to function the injection point must be at the bottom of the coal seam

An Underground Coal Gasification Experiment: Hoe.Creek II

Abstract In this experiment the scheme of linked vertical wells for in-situ coal gasification was used with an 18.3-m well spacing. The experiment took 100 days for air-flow testing, reverse-combustion linking, forward-combustion gasification, and postburn steam flow. Air was used for gasification except for a 2-day test with oxygen and steam flow. Reverse-combustion linking took 14 days at 1.6 m/day and used 0.40 Mgmol of air per meter of link. At least two linkage paths were formed. The detected links stayed below the 3 m level in the 7.6 m coal seam; however, the product flow from the forward-burn gasification probably followed the coal-overburden interface, rather than the reverse-burn links at the 3-m level. Forward-burn gasification took 58 days and produced a total of 232 Mgmol (194 Mscf) of gas with an average heating value of 96 kJ/gmol (108 Btu/scf(. During the oxygen-steam test, the heating value averaged 235 kJ/gmol (265 Btu/scf). The coal recovery was 1310 m3 (1950 ton). Gasification was term...

Correlation of Laser-Induced Damage to Phase Objects in Bulk Fused Silica

The Optical Sciences Laser (OSL) Upgrade facility, described in last years proceedings, is a kJ-class, large aperture (100cm2) laser system that can accommodate prototype optical components for large-scale inertial confinement fusion lasers. High-energy operation of such lasers is often limited by damage to the optical components. Recent experiments on the OSL Upgrade facility using fused silica components at 4 J/cm2 (351-nm, 3-ns) have created output surface and bulk damage sites that have been correlated to phase objects in the bulk of the material. Optical Path Difference (OPD) measurements of the phase defects indicate the probability of laser-induced damage is strongly dependent on OPD.

Hoe Creek No. 2: Underground Gasification Experiment With Air And Oxygen/Steam Injection Periods

This paper presents results from the Lawrence Livermore Laboratory Hoe Creek No. 2 underground coal-gasification experiment. The experiment used an injection well and a production well 18.7 m apart and alternating periods of air and oxygen/steam injection. Both low- and medium-heating-value gas was produced. Fourteen days of reverse combustion linked the injection and production wells and was followed by 58 days of forward-combustion gasification. The first five days of gasification produced good-quality gas, with the higher heating value averaging 125 kJ/mol (140 Btu/scf). After this period, the burn was along the top of the coal seam, which sharply lowered the gas quality. The high burn probably resulted from the injection-well casing being broken or burned off at the top of the coal seam. Switching injection to the bottom of the seam resulted in good-quality gas until the end of the experiment. Forward gasification consumed 1310 m/sup 3/ (1952 tons) of coal. Air injection produced gas that averaged 94 kJ/mol (105 Btu/scf), and a two-day oxygen/steam burn produced gas of medium heating value: 225 to 270 kJ/mol (250 to 300 Btu/scf), with no operational or safety problems. The same geometry that produced poor-quality gas with air produced good-quality gas with oxygen/steam.