摘要:

The singles-doubles (SD) method, in which single and double excitations of the Hartree-Fock wave function are summed to all-orders in perturbation theory, is discussed and applied to valence removal energies, hyperfine constants, and transition matrix elements. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56557

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A selection of recent theoretical results revealing new phenomenology in the photoionization and electron elastic scattering properties of multicharged atomic ions. Particularly striking is the non-smooth behavior of cross sections along isoelectronic and isonuclear sequences of ions, indicating that, although ionic phenomena become simpler eventually, this does not happen monotonically or quickly. This has importance concerning the possibility of transferring our vast knowledge of neutrals to ionic species. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56578

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A variety of electron emission processes have been studied in detail for both atomic and molecular systems, using a highly efficient experimental system comprising two time-of-flight (TOF) rotatable electron energy analyzers and a 3rd generation synchrotron light source. Two examples are used here to illustrate the obtained results. Firstly, electron emission in the HCl molecule have been mapped over a 14 eV wide photon energy range over the Cl 2p ionization thresholds. Particular attention is paid to the dissociative core-excited states, for which the Auger electron emission shows photon energy dependent features. Also, the evolution of resonant Auger to the normal Auger decay distorted by post collision interaction has been observed and the resonating behavior of the valence photoelectron lines studied. Secondly, an atomic system, neon, in which excitation of doubly excited states and their subsequent decay to various accessible ionic states has been studied. Since these processes only occur via inter-electron correlations, the many-body dynamics of an atom can be probed. Electron angular distributions following the decay of certain resonances to a parity-unfavored continuum exhibits significant deviation from LS coupling predictions, which is surprising for such a light atom. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56561

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Observations of significant volume recombination within the Alcator C-Mod divertor plasma and in the edge plasma (MARFE) are described. The recombination occurs in regions whereTe≲1&hthinsp;eVandne≳1×1021&hthinsp;m−3.The determinations of the recombination rates are made by measuring theD0Lyman and/or Balmer spectra and by using a collisional radiative model describing the level populations, ionization and recombination ofD0.In regions of strong recombination the upper levels(n≳4)populations are close to those determined by Saha-Boltzmann distribution and are independent of the ground state density. Thus the intensities of lines from these levels are related to the recombination rate, and curves determining the number of ‘recombinations per photon’ are calculated.Ly&bgr;line emission is shown to be trapped in some cases, meaning thatLy&agr;can be strongly trapped. Since opacity affects the recombination rates, the effects of the trapping ofLy&agr;,&bgr;photons on the ‘recombinations per photon’ curves are calculated and considered in the recombination rate determinations. Total recombination rates in the detached divertor plasma and in MARFEs located at the periphery of the main plasma are determined. Recombination can be a significant sink for ions. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56565

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A description of the carbon transport and sputtering physics contained in the Monte Carlo Impurity (MCI) transport code is given. Examples of statistically significant carbon transport pathways are examined using MCI’s unique tracking visualizer and a mechanism for enhanced carbon accumulation on the high field side of the divertor chamber is discussed. Comparisons between carbon emissions calculated with MCI and those measured in the DIII–D tokamak are described. Good qualitative agreement is found between 2D carbon emission patterns calculated with MCI and experimentally measured carbon patterns. While uncertainties in the sputtering physics, atomic data, and transport models have made quantitative comparisons with experiments more difficult, recent results using a physics based model for physical and chemical sputtering has yielded simulations with about 50&percent; of the total carbon radiation measured in the divertor. These results and plans for future improvement in the physics models and atomic data are discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56566

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This paper summarizes recent calculations of the radiative cooling coefficient for molybdenum(Z=42),krypton(Z=36)and argon(Z=18).The radiative processes considered are collisional-radiative line emission, dielectronic recombination line emission, and radiative recombination and bremsstrahlung continuum emission. Collisional-radiative line emission dominates the power loss channels for a given impurity at all but the highest plasma electron temperatures. The atomic data for the line emission are computedab initiowith the HULLAC atomic physics suite of codes. Relativistic,ab initioatomic physics data are used to compute ionization and recombination rate coefficients; the resulting charge state distribution and recombination rates are used to estimate the radiative power from recombination processes. The calculations in the present work are benchmarked against absolute measurements of ion brightness profiles in the Frascati Tokamak Upgrade plasma. Integrated measurements from tokamak plasmas such as bolometry are then simulated. The atomic physics data used to predict the emissivity of individual ions is validated; the calculated cooling coefficients agree well with bolometric measurements. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56558

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.56559

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Experimental efforts have started for bringing (sub-) picosecond time resolution in pump-probe X-ray diffraction and absorption spectroscopy of transient chemical, biological or physical phenomena. Among the various pulsed X-ray sources available, ultrafast laser-produced plasmas are very promising for the generation of subpicosecond X-rays. We have significantly progressed toward a better understanding of ultrafast (≈100 fs) laser-matter interaction at moderate(≈5×1016&hthinsp;W/cm2)intensities. We have found that fast electron production and non-thermalK&agr;emission peak for a plasma scale length where resonance absorption is maximized. The plasma scale length can be efficiently controlled by using a prepulse of variable relative intensity and delay. Targets of different substrate and overcoat layer materials have been used to obtain informations on the anisotropy of the electron distribution function and on hot electron energy transport. Experimental results are found in satisfactory good agreement with 1-D hydrodynamic and particle-in-cell simulations. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56560

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present recent results of x-ray laser amplification of spontaneous emission in Ne-like and Ni-like transient collisional excitation schemes. The plasma formation, ionization and collisional excitation can be optimized using two laser pulses of 1 ns and 1 ps duration at table-top energies of 5 J in each beam. High gain of 35 cm−1has been measured on the 147 Å4d→4pJ=0→1transition of Ni-like Pd and is a direct consequence of the nonstationary population inversion produced by the high intensity picosecond pulse. We report the dependence of the x-ray laser line intensity on the laser plasma conditions and compare the experimental measurements with hydrodynamic and atomic kinetics simulations for Ne-like and Ni-like lasing. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56567

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Until a few years ago, calculations for electron scattering from atoms and ions were typically performed using non-perturbative close-coupling-type approximations for low impact energies and perturbative Born-type methods in the high-energy regime. Especially for singly and doubly ionized targets, however, neither one of those methods is particularly reliable for the “intermediate energy regime”, i.e., impact energies near and up to about five times the ionization threshold. This gap has recently been closed by the convergent close-coupling (CCC), the R-Matrix with pseudo-states (RMPS), the intermediate-energy R-matrix (IERM), and time-dependent lattice methods. The principal ideas behind these approaches are introduced and some example cases, illustrating the need for using such sophisticated approaches, are discussed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.56568

出版商:AIP    

年代:1998

数据来源: AIP