摘要:

An absence of fundamental atomic plasma chemistry data (e.g. electron impact cross‐sections) hinders the application of plasma process models in semiconductor manufacturing. Of particular importance is excited state plasma chemistry data for metallization applications. This paper describes important plasma chemistry processes in the context of high density plasmas for metallization application and methods for the calculation of data for the study of these processes. Also discussed is the development of model data sets that address computational tractability issues. Examples of model electron impact cross‐sections for Ni reduced from multiple collision processes are presented. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516290

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

By photoionizing a sample of laser‐cooled xenon atoms, we create ultracold neutral plasmas with initial temperatures of 1–1000 K and densities as high as 1010cm−3. The plasma is formed by the trapping of electrons by the residual positive charge that is left after some electrons initially leave the sample. We excite plasma oscillations with applied radio frequency fields and use this to monitor the expansion of the unconfined plasma. We have observed significant recombination of the plasma into Rydberg atoms (up to 20 &percent;). At these low temperatures, the only traditional form of recombination that could be significant is three‐body recombination (TBR). Recent theoretical studies of ultracold plasmas, and prospects for future experiments, are discussed. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516291

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Cold dense samples of Rydberg atoms spontaneously evolve into ultracold plasmas. Initially some cold ions are formed by black body photo ionization and collisions, and they trap electrons freed later. It appears that these trapped electrons initiate an avalanche of ionization of the remaining Rydberg atoms. How quickly the avalanche occurs is determined in part by how rapidly energy is supplied to the system. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516292

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Low fluence laser produced plasmas are used in many applications: from ion sources to material synthesis. Our work focuses on developing a quantitative description of these ablation plasmas through the interpretation and analysis of time‐ and spatially‐resolved spectroscopic measurements with detailed spectral modeling. To this end, in a series of experiments performed at Sandia National Laboratories, laser generated Li‐Ag plasma plumes were produced by irradiation of solid targets using a Nd pulsed laser. Time‐ and spatially‐resolved optical spectra were recorded with a framing spectrograph. In order to limit the gradients along a direction perpendicular to the target’s normal, targets with strips of Li‐Ag coated on top of Pt were used. The Pt plume collisionally confines the Li‐Ag, thus reducing the Li‐Ag lateral expansion. The spectra display line transitions in Li and Ag atoms. A spectroscopic model based on time‐dependent collisional‐radiative atomic kinetics, detailed line shapes, and radiation transport was used to describe plasma parameters both spatially and temporally. In particular, this analysis has revealed that level populations in laser‐ablated plumes may behave in a time‐dependent manner, i.e. not in Local Thermodynamic Equilibrium (LTE). The time‐scales associated with these phenomena and the interpretation of spectral data critically depends on the details of the atomic kinetic model and the quality of the rate coefficients. In order to generate accurate atomic data for atoms present in the plasma, a semi‐empirical technique has been implemented in the Los Alamos suite of atomic structure and electron scattering codes. Details of the spectral model and analysis results will be discussed. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516293

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

X‐ray induced fluorescence has been used to measure elemental number densities of all constituents in a ceramic metal‐halide discharge lamp. High‐energy synchrotron radiation generated at the Sector 1 Insertion Device beam line at the Advanced Photon Source induced K‐shell fluorescence in the high‐pressure arc plasma. High signal‐to‐noise fluorescence spectra of Hg, Dy, Cs and I could be simultaneously obtained. A method for absolute calibration enabled us to map density distributions of all constituents throughout the whole lamp with a spatial resolution of 1 mm3. Elemental ratios show clear evidence of radial de‐mixing of metal additives. A possible explanation for the on‐axis depletion is ambipolar transport of positive ions out of the center of the arc. The highly successful experiments demonstrate the utility of modern x‐ray sources and methods for diagnostics as new tools for improved understanding of high‐pressure arc discharges. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516294

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

In this work we present temperature diagnostics of an expanding laser‐produced argon plasma. A short‐pulse (35fs) laser with an intensity ofI= 1017W/cm deposits ∼ 100 mJ of energy into argon clusters. This generates a hot plasma filament that develops into a cylindrically expanding shock. We develop spectral diagnostics for the temperatures of the argon plasma in the shock region and the preionized region ahead of the shock. A collisional‐radiative model is applied to explore line intensity ratios derived from Ar II‐Ar IV spectra that are sensitive to temperatures in a few eV range. The results of hydrodynamic simulations are employed to derive a time dependent radiative transport calculation that generates the theoretical emission spectra from the expanding plasma. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516295

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

We report on a collaborative effort that has led to the development of a spectroscopic method for the determination of the gradient structure in ICF implosion cores based on the self‐consistent analysis of simultaneous X‐ray monochromatic images and X‐ray line spectra. This technique is applied to a series of stable and spherically symmetric implosion experiments where Ar‐doped D2‐filled plastic shells were driven with the GEKKO and OMEGA laser systems. Argon K‐shell X‐ray line spectra were measured with streak crystal spectrometers, while X‐ray monochromatic imagers recorded core images based on the Ar He&bgr; line. The analysis self‐consistently determines the temperature and density gradients that yield the best fits to both the spatial distribution of monochromatic emissivity and spectral line shapes. A multi‐objective genetic algorithm is used to efficiently perform the analysis. This measurement is critical for understanding the spectra formation and plasma dynamics associated with the implosion process. In addition, since the results are independent of hydrodynamic simulations they are important for the verification and benchmarking of detailed fluid dynamic models of high energy density plasmas. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516296

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The success in building ultrashort pulse lasers capable of delivering higher and higher intensities have pushed laser‐solid interaction experiments into a new regime where vos/c approaches 1. We have performed experiments to study the K‐shell aluminum emission spectra from thin foils heated with an ultrashort pulse laser. The foils are illuminated at an intensity of 1 × 1019W/cm2. After heating, minimal radiation cooling and longitudinal heat conduction occur due to the targets’ low atomic number and thickness, allowing hydrodynamic expansion to dominate the cooling process and simplifying the analysis. The time resolved Helium like 1s2‐1s2p(1P) (He&agr;), 1s2‐1s3p(1P) (He&bgr;), and 1s2‐1s4p(1P) (He&ggr;) spectrum is collected with a 500 fs x‐ray steak camera interfaced to a two crystal von Hamo¨s spectrograph. The spectra from these plasmas have shown interesting and unusual features. In particular, exotic satellites have been observed when high intensity ultrashort pulse lasers interact with solids. The satellite emission brightness relative to the resonance lines suggest an expectedly large fraction of Li‐like, Be‐like, and B‐like ions. An electron beam generated in the field of the laser is offered as an explanation of the observed satellite emission. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516297

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The systematic experimental studies of plasma produced upon the interaction of ultra‐short laser pulses with cluster targets are carried out using the methods of x‐ray spectroscopy. The dependence of the plasma parameters on the initial properties of a cluster target such as the design of a supersonic nozzle, the average size of clusters, and their spatial distribution as well as the laser‐pulse properties of duration and contrast are studied. The plasma diagnostics is performed using the model of spectra formation that provides a good agreement with the experimental data. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516298

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Hullacis an integrated code for calculating atomic structure and cross sections for collisional and radiative atomic processes, aimed at complex spectra of heavy ionized atoms. It is based on relativistic quantum mechanical calculations including configuration interaction. The collisional cross sections are calculated in the distorted wave approximation. The target and continuum wavefunctions are obtained consistently. The theory and algorithms are presented, emphasizing the various novel methods that were developed to obtain accurate results very efficiently. In particular we describe the Parametric Potential method used for both bound and free orbitals, and theNjgrafgraphical method used in the calculation of the angular momentum part of the matrix elements. Collision cross sections are obtained extremely efficiently, thanks to the Factorization‐Interpolation method applied in the derivation of collisional rates, and the Phase Amplitude approach for calculating the continuum orbitals. Special effort was devoted to ensure the simplicity of use. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516299

出版商:AIP    

年代:1902

数据来源: AIP