摘要:

Theoretical calculations of electron‐impact ionization and recombination in positively charged ions are reviewed and compared to cross section measurements. In the case of ionization, the contributions of excitation autoionization and resonant recombination followed by double autoionization are considered. The excitation‐autoionization contributions can dominate the total ionization cross section even for highly ionized species. In addition, we present the results of fully relativistic calculations of ionization cross sections obtained from lowest‐order QED theory for H‐like and He‐like uranium. Finally, we consider the contribution of dielectronic recombination (DR) to electron‐impact recombination. Comparison of theoretical calculations of DR for He‐like and Li‐like carbon and oxygen ions with recent high‐resolution, merged‐beam measurements, using the electron cooler at Aarhus, seem to indicate that total DR cross sections can be accurately determined from the isolated‐resonance approximation. The effects of electric fields on DR are briefly discussed.

ISSN:0094-243X    

DOI:10.1063/1.39291

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recent spectroscopic data clearly indicate that both relativistic and quantum electrodynamic (QED) effects are indispensable in understanding the spectra of highly‐charged ions. QED effects are discernible even in spectra involving M‐ and N‐shell electrons. Current understanding and theoretical capability in predicting relativistic and QED corrections in atomic structure are reviewed.

ISSN:0094-243X    

DOI:10.1063/1.39286

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present the general trends in comparing experimental and theoretical electron capture cross sections for both dominantly and non‐dominantly populated states in collisions of fully stripped carbon or oxygen ions on atomic hydrogen. The experimental results have been obtained by means of Photon Emission Spectroscopy. With this technique we have also measured the HeII (n=4 → n=3) emission profiles along the ion beam axis in collisions of He2+on atomic hydrogen. We have succeeded for the first time to identify from the emission profiles the separate contributions from the various quasi‐degenerate 4l‐states of He+produced in the electron capture process.

ISSN:0094-243X    

DOI:10.1063/1.39297

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The autoionization rates of Ba 6p1/2nk Stark states have been measured in static and 9 GHz microwave fields using a multistep laser excitation technique. The experiments have been performed for a range of field values between zero field and the 1/16n4classical ionization limit. The results of all the experiments can be reproduced quite well by a linear Stark effect model. The connection between these experiments and the actual situation in a plasma is discussed along with implications for dielectronic recombination.

ISSN:0094-243X    

DOI:10.1063/1.39292

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

ALADDIN is an atomic physics database system which has been developed in order to provide a broadly‐based standard medium for the exchange and management of atomic data. ALADDIN consists of a data format definition together with supporting software for both interactive searches as well as for access to the data by plasma modeling and other codes. 8AB The ALADDIN system is designed to offer maximum flexibility in the choice of data representations and labeling schemes, so as to support a wide range of atomic physics data types and allow natural evolution and modification of the database as needs change. Associated dictionary files are included in the ALADDIN system for data documentation. The importance of supporting the widest possible user community was also central to be ALADDIN design, leading to the use of straightforward text files with concatentated data entries for the file structure, and the adoption of strict FORTRAN 77 code for the supporting software. This will allow ready access to the ALADDIN system on the widest range of scientific computers, and easy interfacing with FORTRAN modeling codes, user developed atomic physics codes and database, etc. This supporting software consists of the ALADDIN interactive searching and data display code, together with the ALPACK subroutine package which provides ALADDIN datafile searching and data retrieval capabilities to user’s codes.ALADDIN has been adopted as the standard international atomic physics data exchange format for magnetic confinement fusion applications by the International Atomic Energy Agency (IAEA). Entry of critically evaluated atomic data sets into ALADDIN format is to be coordinated by the IAEA atomic and Molecular Data Unit, which will also coordinate long‐term development and distribution of updated software and documentation. The increasingly widespread adoption of the ALADDIN data format can be expected to greatly facilitate access to atomic data both within and outside of this original fusion application area.

ISSN:0094-243X    

DOI:10.1063/1.39293

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Large amounts of accurate atomic data have been calculated in a collaborative effort referred to as the Opacity Project. The computational methods and various physical processes of interest are discussed here, with reference to the opacity spectrum and some preliminary results.

ISSN:0094-243X    

DOI:10.1063/1.39294

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Persisting discrepancies between theory and observation in a number of astrophysical properties has led to the conjecture that opacity databases may be inaccurate. The OPAL opacity code has been developed to address this question. The physical basis of OPAL removes several of the approximations present in past calculations. For example, it utilizes a much larger and more detailed set of atomic data than was used to construct the los Alamos Astrophysical Library. This data is generated online, in LS or intermediate coupling, from prefitted analytic effective potentials and is of similar quality as single configuration, relativistic, self‐consistent‐field calculations. The OPAL code has been used to calculate opacities for the solar core and for Cepheid variable stars. In both cases, significant increases in the opacity compared to the Los Alamos Astrophysical Library were found.

ISSN:0094-243X    

DOI:10.1063/1.39295

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

With the advent of new technologies enabling high‐near normal incidence reflectivities in the soft x‐ray range, new types of plasma spectroscopy diagnostics such as for instance, short time scale fluctuation measurements based on line emission will become feasible both at the edge and in the center of magnetically confined fusion plasmas. Also, in those cases in which time resolved local electron temperature and density estimates are needed, the classical spectroscopic method of line intensity ratios is used. Such measurements require an accurate knowledge of the atomic processes determining the spectral line intensities. The present paper discusses some less accounted for processes responsible for level populations, such as the effect of resonances on the electron impact excitation cross sections, inner shell ionization of M and L‐shell charge states, and excitation‐autoionization. It is shown that these processes may have veery important effects on the XUV radiative patterns of high temperature plasmas.

ISSN:0094-243X    

DOI:10.1063/1.39296

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Diagnostic techniques based on laser optogalvanic spectroscopy and laser induced fluorescence are providing spatial and temporal maps of key quantities in glow discharge plasma. Such maps are particularly useful in studying the cathode region. This region is of fundamental interest because of the failure of the local field approximation, and of practical interest because of widespread use of glow discharges in plasma processing and other areas. Laser techniques are used to map space charge electric fields, charged particle densities, average energies of charged particles, flux densities of charged particles, excited atom densities, and other key quantities. These maps provide valuable insights into the dominant physical processes in the cathode region and provide a stringent test of numerical models. A more quantitative understanding of the cathode region is emerging from laser studies and from advanced modeling efforts.

ISSN:0094-243X    

DOI:10.1063/1.39279

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The cross sections for production of excited H atoms by electron collisions exhibit significantly different variations with the principal quantum number of the product atoms, depending on whether the production mechanism involves dissociative excitation of H2, or direct excitation from ground‐state H atoms. It is also known that, in a tokamak plasma, the excited state which constitutes the boundary between the corona‐phase and the ladder‐like excitation‐ionization phase is located close to the states from which the lower members of Lyman or Blamer lines are emitted. On the basis of these premises we developed a method to determine the densities of atomic hydrogen, molecular hydrogen, and electrons from the observed Balmer or Lyman line intensities. We applied this method to the WT‐III tokamak and found that, in the edge region of the main plasma, the H2density was forty times higher than the H atomic density. We discuss the possible use of a similar method for the treatment of a deuterium plasma or a plasma containing hydrocarbons.

ISSN:0094-243X    

DOI:10.1063/1.39298

出版商:AIP    

年代:1990

数据来源: AIP