摘要:

Nuclear fusion research, using magnetically confined plasmas, needs a great amount of atomic data in the fields of plasma diagnostics, plasma spectroscopy and modelling. Conventional spectroscopy and some specialised techniques are being used for analysing plasma behavior and plasma composition. Hydrogen data are required, as well as coefficients for impurities originating from the vacuum vessel walls and protection tiles. Some noble gases are being used for radiative cooling or transport studies of highly ionized ions. For measuring metal concentrations, diagnostic lines from the plasma interior are recorded, sometimes of highly ionized species like Zn-like tungsten. The ionization balance and the emitting shells must be calculated on the basis of the relevant atomic data and of the transport coefficients. For high heat-load areas, carbon is mostly used at present, which is fully ionized in the plasma and can only be measured by charge-exchange recombination spectroscopy. Impurity particle influxes at the boundary are derived from lines of neutrals or low ionization stages, a method, which can also be extended to the band emission of molecules. In this way, chemical erosion of carbon is being investigated. In cold divertor plasmas, hydrogen molecules also play some role, e.g. enhancing hydrogen ion recombination. In addition to the usual coefficients for ionization, recombination, charge exchange and radiation for all relevant elements, molecular data are required in model calculations of the plasma boundary and of divertors. Some examples of interpretation methods and experimental results in these fields are presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336275

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

With the launches of the Chandra X-ray Observatory (CXO) and the X-ray Multimirror Mission (XMM), high resolution X-ray spectroscopy of cosmic sources has begun. Early, deep observations of three stellar coronal sources will provide not only invaluable calibration data, but will also give us benchmarks for the atomic data under collisional equilibrium conditions. Analysis of the Chandra X-ray Observatory data, and data from other telescopes taken simultaneously, for these stars is ongoing as part of the Emission Line Project. Goals of the Emission Line Project are (1) to determine and verify accurate and robust diagnostics and (2) to identify and prioritize issues in fundamental spectroscopy which will require further theoretical and/or laboratory work. The Astrophysical Plasma Emission Database will be described in some detail, as it is introducing standardization and flexibility into X-ray spectral modeling. Spectral models of X-ray astrophysical plasmas can be generally classified as dominated by either collisional ionization or by X-ray photoionization. While the atomic data needs for spectral models under these two types of ionization are significantly different, there are overlapping data needs, as I will describe. Early results from the Emission Line Project benchmarks are providing an invaluable starting place, but continuing work to improve the accuracy and completeness of atomic data is needed. Addtionally, we consider the possibility that some sources will require that both collisional ionization and photoionization be taken into account, or that time-dependent ionization be considered. Thus plasma spectral models of general use need to be computed over a wide range of physical conditions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336276

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In this review, the theory of low energy electron scattering by light atoms and ions is first presented. The theory is then extended to treat electron scattering by heavy atoms and ions where relativistic effects are important. Electron scattering by atoms and ions at intermediate and high energies, and the threshold behavior of the ionization cross section are then reviewed. Finally the theory of scattering of electrons by molecules is discussed, where the possibility of exciting degrees of freedom associated with the nuclear motion is considered. In all of these areas, computer program packages which enable accurate scattering data to be calculated are referenced. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336277

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The previous decade has seen immense progress in the field of electron-atom scattering. The availability of accurate computed data has revitalized numerical modeling of plasmas in astrophysics, fusion, lighting, and elsewhere. Here we summarize the contribution that the Convergent Close-Coupling (CCC) method has made to the generation of such data. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336278

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Much effort has been recently devoted to the experimental determination of absolute partial and total electron impact ionization cross sections of molecules and radicals due to the ever increasing importance of these cross sections in many applications such as low- and high-temperature plasma physics and chemistry, atmospheric physics and mass spectrometry. In addition supporting calculations have been recently developed in order to allow the analytic quantitative description of these cross section functions for modeling codes. This review summarizes recent experimental and theoretical progress in this area of electron impact ionization including also a short description of (i) recent advances in the field of electron/ion collisions (i.e., kinetic energy release distributions in dissociative excitation reactions of molecular ions) and (ii) a novel approach to the determination of electron induced appearance energies. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336279

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In this paper we show, on a few examples, how the merging beam method is applied to measure absolute cross sections of low energy rearrangement processes such as resonant electron transfer, transfer ionization, and associative ionization. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336280

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The binary-encounter-Bethe (BEB) model for calculating electron-impact ionization cross sections for molecules is described with emphasis on polyatomic molecules and their radicals and ions. The BEB model provides an analytic formula for the cross section. The formula is for each molecular orbital, and requires only three numbers from the initial state of the target molecule: the electron occupation number, the orbital binding energy, and the orbital kinetic energy. The sum of the orbital cross sections provides the molecular cross section. The BEB model produces reliable ionization cross sections from the threshold to several keV in incident electron energy for neutral molecules and ions. The BEB cross sections for some fluorine-containing radicals are almost a factor of two larger than available experimental values. Molecular constants are included to generate BEB cross sections forH2,C2F6,H2+,CH3,CFx,BFx,BClxforx=1–3,and several unsaturted molecules relevant to hydrocarbon combustion. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336281

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Recent advances in the resolution of observational data have required a much greater degree of accuracy in the determination of oscillator strengths than has been necessary in the past. We discuss how corresponding theoretical advances are leading to improved accuracy in the calculation of wave functions of atomic states, resulting in oscillator strengths whose uncertainties are within acceptable limits. We show the importance of using experimental energies in refiningab initiocalculations, and we illustrate these developments by considering difficult transitions in Mg II, Na III, and Fe II. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336282

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This review paper presents illustrative cases showing how Quantum Chemistry calculations can be an alternative to laboratory experiments. After a short description of the basic concepts and methods used, the presentation is centered on the ability of computational chemistry to produce data pertinent to solving problems of astrophysical interest ranging from identification of new molecules to IR emission analysis and rate constants determinations. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336283

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A short summary is given of the methods used by the IRON Project team in order to supply users of atomic data with reliable oscillator strengths and radiative transition probabilities. Available results and corresponding references are listed. A few cases are discussed briefly with a view to illustrate the progress made and the difficulties encountered. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1336284

出版商:AIP    

年代:1900

数据来源: AIP