摘要:

The increasing power and availability of supercomputers during the last decade led to significant progress in the theory of multicharged ion interactions. However, important tests of many theoretical predictions were lacking, and have become possible only quite recently as new capabilities have been realized in the laboratory. This paper broadly surveys some of these experimental developments, and their impact on our understanding of collisional interactions of multicharged ions. The scope is limited to measurements made with monoenergetic beams.

ISSN:0094-243X    

DOI:10.1063/1.42475

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Recombination of highly charged ions and free electrons is studied in interacting‐beam experiments. Beside direct recombination into bound states by radiative capture a variety of resonant recombination phenomena is observed. Resonant recombination produces a highly excited, usually short lived electron‐ion compound which can stabilize by the emission of photons and/or electrons. Depending on this emission, the final charge state of the ion can be one less than the parent charge state, but it can also be higher and thus a net single or multiple ionization of the ion is observed after the initial recombination.

ISSN:0094-243X    

DOI:10.1063/1.42470

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The electron beam ion trap (EBIT) at LLNL is a unique device designed to measure the interactions of electrons with highly‐charged ions. We describe three methods used at EBIT to directly measure the dielectronic recombination (DR) process: (1) The intensity of the stabilizing X rays is measured as a function of electron beam energy; (2) The ions remaining in a particular ionization state are counted after the electron beam has been held at a fixed electron energy for a fixed time; and (3) High‐resolution spectroscopy is used to resolve individual DR satellite lines. In our discussions, we concentrate on the KLL resonances of the heliumlike target ions (V21+to Ba54+), and the LMM resonances of the neonlike target ions (Xe44+to Th80+).

ISSN:0094-243X    

DOI:10.1063/1.42473

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A review of the recent work performed in the study of spectral line broadening in dense plasma is presented. The work reviewed will cover recent advances in the theoretical development of line broadening and touch only briefly on the experimental aspects of the problem. Efforts to develop line shape calculations appropriate for spectral synthesis, which can be used in the study of opacities and non‐LTE radiative transfer will also be discussed. A brief summary of the currently available resources for line shapes will be presented. A bibliography of the papers used in the review is provided.

ISSN:0094-243X    

DOI:10.1063/1.42474

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Layered targets of aluminum and fused silica have been irradiated by 80 fs prepulse free laser pulses at 1017W/cm2laser irradiance. Time‐integrated x‐ray spectra obtained in the 0.7–0.9 nm wavelength range show both resonance lines from Al11+ions and K&agr; lines from Al0+‐Al5+ions. Conversion efficiency measurements give x‐ray intensities of a few TW/cm2. A detailed analysis of K&agr; emission points out the role of energetic electrons in the interaction physics. Based on a detailed comparison of experiments with hydrodynamic simulations, it is concluded that K&agr; emission is not longer than the laser pulse duration.

ISSN:0094-243X    

DOI:10.1063/1.42480

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Recently developed sub‐picosecond pulse lasers have been used to create hot, near solid density plasmas. Since these plasmas are nearly in local thermodynamic equilibrium (LTE), their emission spectra involve a huge number of populated configuration. A typical spectrum is a combination of many unresolved clusters of emission, each containing an immense number of overlapping, unresolvable bound‐bound and bound‐free transitions. Under LTE, or near LTE conditions, traditional detailed configuration or detailed term spectroscopic models are not capable of handling the vast number of transitions involved. The average atom (AA) model, on the other hand, accounts for all relevant transitions, but in an oversimplified fashion that ignores all spectral structure. The Super Transition Array (STA) model, which we have developed in recent years, combines the simplicity and comprehensiveness of the AA model with the accuracy of detailed term accounting. The resolvable structure of spectral clusters is revealed by successively increasing the number of distinct STA’s, until convergence is attained. The limit of this procedure is a detailed unresolved transition array (UTA) spectrum, with a term‐broadened line for each accessible configuration‐to‐configuration transition, weighted by the relevant Boltzman population.In practice, we have found that this UTA spectrum is actually obtained using only a few thousand to tens of thousands of STA’s (as opposed, typically, to billions of UTAs). The central result of STA theory is a set of formulas for the moments (total intensity, average transition energy, variance) of an STA. In calculating the moments, we use detailed relativistic first order quantum transition energies and probabilities. The energy appearing in the Boltzman factor associated with each level in a superconfiguration is the zero order result corrected by a superconfiguration averaged first order correction. As the number of configurations in a superconfiguration is successively decreased, this becomes equivalent to using exact first order configuration average energies. In addition, orbital relaxation can be accounted for by recalculating orbitals and energies for each STA in a potential optimized for the particular set of configurations. Examples and application to recent measurements are presented.

ISSN:0094-243X    

DOI:10.1063/1.42481

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In order to test and improve opacity models, we are performing experiments to accurately characterize and measure the opacity of high‐Z plasmas. In the experiments the NOVA laser at Lawrence Livermore National Laboratory is used to indirectly heat tamped thin foil targets containing mid to high‐Z ions of interest which are co‐mixed with low‐Z ions for spectroscopic determinations of plasma conditions. One of the NOVA beams is used to create a source of x‐rays for backlighting the plasma face‐on, while another beam is used to perform a radiograph of the expanding sample edge‐on. X‐rays that pass through and around the plasma are simultaneously measured on high resolution crystal spectrometers, and the opacity is measured by comparing the direct and attenuated x‐ray spectra. Plasma density is determined from the spatial extent of the expanded plasma, and plasma temperature is inferred from the ionization distribution of the low‐Z ions doped in the plasma. Predictions of the high‐Z opacity are then compared with data using measured conditions as input. These are the first high temperature opacity measurements in which sample conditions are simultaneously determined. We present measurements and predictions for a spectroscopic experiment using a comixture of aluminum and niobium. We discuss plans for future improvements, and for spectroscopic measurements in the spectral region determining Rosseland mean opacities.

ISSN:0094-243X    

DOI:10.1063/1.42485

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Many X‐ray spectra emitted by laser‐irradiated high‐Z elements are dominated by the intense pseudocontinuum originating from 3d‐4finner‐shell resonance transitions. In this paper, some of the particular properties of the 3d‐4finner‐shell excited levels are presented and the implications on the interpretation of the observed spectra are discussed.

ISSN:0094-243X    

DOI:10.1063/1.42482

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Bound states in dense plasma show strongly density‐dependent characteristics. First the shifts of the energy levels and the corresponding influence on the ionization equilibria are analyzed. The stability analysis of the thermodynamic functions shows the existence of additional phase transition at high temperatures and high pressures due to nonideality effects. The nonideality also influences the kinetic rate coefficients and changes the time behaviour of the electron populations of the bound states.

ISSN:0094-243X    

DOI:10.1063/1.42483

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Charge exchange and beam emission spectroscopy in magnetic confinement fusion plasmas are reviewed. The range of spectral phenomenology is illustrated from the JET tokamak using fast deuterium and helium beams. The helium observations are new. The atomic reactions concerned in the emission and their interplays are summarised. The state of cross‐section data for the analysis is briefly assessed.

ISSN:0094-243X    

DOI:10.1063/1.42476

出版商:AIP    

年代:1992

数据来源: AIP