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Evaporation monitoring and composition control of alloy systems with widely differing vapor pressures

Description: Lawrence Livermore National Laboratory is developing sensors and controls to improve and extend electron beam materials processing technology to alloy systems with constituents of widely varying vapor pressure. The approach under development involves using tunable lasers to measure the density and composition of the vapor plume. A laser based vaporizer control system for vaporization of a uranium-iron alloy has been previously demonstrated in multi-hundred hour, high rate vaporization experiments at LLNL. This paper reviews the design and performance of the uranium vaporization sensor and control system and discusses the extension of the technology to monitoring of uranium vaporization. Data is presented from an experiment in which titanium wire was fed into a molten niobium pool. Laser data is compared to deposited film composition and film cross sections. Finally, the potential for using this technique for composition control in melting applications is discussed.
Date: October 1, 1994
Creator: Anklam, T.M.; Berzins, L.V.; Braun, D.G.; Haynam, C.; McClelland, M.A. & Meier, T.
Partner: UNT Libraries Government Documents Department

Analysis of the e-beam evaporation of titanium and Ti-6Al-4V

Description: An experimental and finite element analysis was performed for the electron-beam evaporation of Ti and Ti-6Al-4V from a bottom-feed system. The bulk evaporation rate was measured by feed consumption, and the pool elevation was held constant by adjusting the feed rate in a closed-loop control system. The instantaneous titanium and aluminum evaporation rates were determined by laser absorption in the vapor plume. Water temperature rises in cooling water circuits provided heat flows, and post-run cross sections revealed the location of the solidification zone. The MELT finite element code was applied to model the steady-state two-dimensional fluid flow and energy transport in the rod. There was good agreement between model and measured values of the heat flows and solidification boundaries for Ti. Measured bulk evaporation rates were similar for Ti and Ti-6-4 with greater variation observed for the Ti values. The model evaporation rates were higher than the measured values, but a similar linear dependence on e-beam power was observed in all cases. In a Ti-6-4 evaporation experiment with steady process conditions, laser absorption measurements showed much larger fluctuations in the evaporation rate for Al than Ti.
Date: February 11, 1998
Creator: Westerberg, K.W.; Merier, T.C.; McClelland, M.A.; Braun, D.G.; Berzins, L.V.; Anklam, T.M. et al.
Partner: UNT Libraries Government Documents Department

Experimental and numerical study of E-beam evaporation of titanium

Description: An experimental and numerical study is performed for the electron- beam evaporation of pure titanium from a bottom fed vapor source. In the experiments, an electron beam operating in the nominal range of 30-40 [kW] was used to evaporate metal from the top of a 3 inch diameter rod. Variations were made in the e-beam power, sweep pattern, and sweep frequency, and the total evaporation rate was measured from feed consumption and laser absorption. The solid-pool interface was obtained from metallographic cross sections of the metal rod. A two-dimensional finite element model was developed for the melt which includes the effect of fluid flow and energy transport in the pool and conduction in the solid. The deformation of the liquid-vapor and solid-liquid interfaces are tracked using a mesh which stretches along spines parallel to the axis of the rod. For the cases considered, high evaporative fluxes and vapor pressures generate significant depressions in the top surface of the pool. Predicted and measured evaporation rates are in good agreement for moderate evaporation fluxes, but discrepancies are larger for the case involving the highest flux and deepest depression.
Date: November 26, 1997
Creator: McClelland, M.A.; Westerberg, K.W.; Meier, T.C.; Braun, D.G.; Berrins, L.V. & Anklam, T.M. Storer, J.
Partner: UNT Libraries Government Documents Department

Ablation of NIF Targets and Diagnostic Components by High Power Lasers and X-Rays from High Temperature Plasmas

Description: The National Ignition Facility (NIF) will consist of 192 laser beams that have a total energy of up to 1.8 MJ in the 3rd harmonic ({lambda} = 0.35 {micro}m) with the amount of 2nd harmonic and fundamental light depending on the pulse shape. Material near best focus of the 3rd harmonic light will be vaporized/ablated very rapidly, with a significant fraction of the laser energy converted into plasma x rays. Additional plasma x rays can come from imploding/igniting capsule inside Inertial Confinement Fusion (ICF) hohlraums. Material from outer portions of the target, diagnostic components, first-wall material, and optical components, are ablated by the plasma x rays. Material out to a radius of order 3 cm from target center is also exposed to a significant flux of 2nd harmonic and fundamental laser light. Ablation can accelerate the remaining material to high velocities if it has been fragmented or melted. In addition, the high velocity debris wind of the initially vaporized material pushes on the fragments/droplets and increases their velocity. The high velocity shrapnel fragments/droplets can damage the fused silica shields protecting the final optics in NIF. We discuss modeling efforts to calculate vaporization/ablation, x-ray generation, shrapnel production, and ways to mitigate damage to the shields.
Date: April 19, 2000
Creator: Eder, D. C.; Anderson, A. T.; Braun, D. G. & Tobin, M. T.
Partner: UNT Libraries Government Documents Department

Evaporation rate and composition monitoring of electron beam PVD processes

Description: Lawrence Livermore National Laboratory (LLNL) is developing sensor and control technology to improve the quality and range of applicability of electron beam PVD. The approach being developed uses tunable lasers to measure, the density and composition of the vapor plume. This paper reviews the principles of operation of laser based sensors and discusses data from experiments in which titanium and niobium are co-vaporized. Laser data agreed well with deposited film compositions and spatial variations in deposited film cross sections. Laser based vapor monitoring appears to have broad applicability and has the potential to extend the use of high rate electron beam PVD.
Date: March 1, 1995
Creator: Anklam, T.M.; Berzins, L.V.; Braun, D.G.; Haynam, C.; Meier, T. & McClelland, M.A.
Partner: UNT Libraries Government Documents Department

Very-high-growth-factor Planar Ablative Rayleigh Taylor Experiments

Description: The Rayleigh-Taylor (RT) instability is an important factor in bounding the performance envelope of ignition targets. This paper describes an experiment for ablative RT instability that for the first time achieves growth factors close to those expected to occur in ignition targets at the National Ignition Facility (NIF). The large growth allows small seed perturbations to be detected and can be used to place an upper bound on perturbation growth at the ablation front resulting from microstructure in the preferred Be ablator. The experiments were performed on the Omega laser using a halfraum 1.2 mm long by 2 mm diameter with a 75% laser entrance hole. The halfraum was filled with {approx} 1 atm of neopentane to delay gold plasma from closing the diagnostic line of sight down the axis of the halfraum. The ablator was mounted at the base of the halfraum, and was accelerated by a two stepped X-ray pulse consisting of an early time section {approx} 100 eV to emulate the NIF foot followed by an approximately constant {approx} 150 eV drive sustained over an additional 5-7ns. It is this long pulse duration and late time observation that distinguishes the present work from previous experiments, and is responsible for the large growth that is achieved. The growth of a 2D sinusoidal perturbation machined on the drive side of the ablator was measured using face-on radiography. The diagnostic view remained open until {approx} 11 ns with maximum growth factors measured to be {approx} 200. The trajectory of the ablator was measured using streaked backlit radiography. The design and analysis of the experiments is described, and implications for experiments on ignition target ablators are discussed.
Date: October 30, 2006
Creator: Bradley, D K; Braun, D G; Glendinning, S G; Edwards, M J; Milovich, J L; Sorce, C M et al.
Partner: UNT Libraries Government Documents Department

Experimental Studies of ICF Indirect-Drive Be and High Density C Candidate Ablators

Description: To validate our modeling of the macroscopic and microscopic hydrodynamic and equation of state response of these candidate ablators to NIC-relevant x-ray drive, a multi-lab experimental program has been verifying the behavior of these new ablators. First, the pressures for onset and termination of melt for both Be and HDC under single or double shock drive has been measured at the Z and Omega facilities. Second, the level and effect of hard x-ray preheat has been quantified in scaled experiments at the Omega facility. Third, a long planar x-ray drive has been developed to check 2D and 3D perturbation growth at the ablation front upon acceleration. The concept has been extended to study growth at and near the ablator-ice interface upon deceleration. In addition, experimental designs for validating the expected low level of perturbation seeding due to possible residual microstructure after melt during first and second shock transit in Be and HDC have been completed. Results so far suggest both Be and HDC can remain ablator choices and have guided pulse shaping designs.
Date: September 5, 2007
Creator: Landen, O L; Bradley, D K; Braun, D G; A.Smalyuk, V; Hicks, D G; Celliers, P M et al.
Partner: UNT Libraries Government Documents Department