Yuri Ralchenko

Accelerated recombination due to resonant deexcitation of metastable states

Abstract In a recombining plasma the metastable states are known to accumulate population thereby slowing down the recombination process. We show that an account of the doubly excited autoionizing states, formed due to collisional recombination of metastable ions, results in a significant acceleration of recombination. A fully time-dependent collisional-radiative (CR) modeling for stripped ions of carbon recombining in a cold dense plasma demonstrates an order of magnitude faster recombination of He-like ions. The CR model used in calculations is discussed in detail.

Review of the NLTE kinetics code workshop

Abstract The first workshop to compare the output from Non-LTE kinetics codes using a standardized set of problems is reviewed. The background for the workshop is discussed and the planning is briefly outlined. The participation and general constraints for the workshop are given. Next the defined cases and a motivation for each case is presented. Some results from the workshop are shown which indicate both the utility of the workshop and some of the difficulties faced by those involved in NLTE kinetics modeling. Plans for the next workshop are discussed in the conclusion.

Spectra of W39+–W47+ in the 12–20 nm region observed with an EBIT light source

We observed spectra of highly ionized tungsten in the extreme ultraviolet with an electron beam ion trap (EBIT) and a grazing-incidence spectrometer at the National Institute of Standards and Technology. Stages of ionization were distinguished by varying the energy of the electron beam between 2.1 keV and 4.3 keV and correlating the energies with spectral line emergence. The spectra were calibrated by reference lines of highly ionized iron produced in the EBIT. Identification of the observed lines was aided by collisional-radiative modelling of the EBIT plasma. Good quantitative agreement was obtained between the modelling results and the experimental observations. Our line identifications complement recent results for W40+–W45+ observed in a tokamak plasma by Putterich et al (2005 J. Phys. B: At. Mol. Opt. Phys. 38 3071). For most lines we agree with their assignment of ionization stage. Additionally, we present new identifications for some allowed and forbidden lines of W39+, W44+, W46+ and W47+. The uncertainties of our wavelengths range from 0.002 nm to 0.010 nm.

Stark broadening of the B III 2s-2p lines

We present a quantum-mechanical calculation of Stark linewidths from electron-ion collisions for the 2s{sub 1/2}-2p{sub 1/2,3/2}, {lambda}=2066 and 2067 {Angstrom}, resonance transitions in BIII. The results confirm previous quantum-mechanical R-matrix calculations, but contradict recent measurements and semiclassical and some semiempirical calculations. The differences between the calculations can be attributed to the dominance of small L partial waves in the electron-atom scattering, while the large Stark widths inferred from the measurements would be substantially reduced if allowance is made for hydrodynamic turbulence from high-Reynolds-number flows and the associated Doppler broadening. {copyright} {ital 1997} {ital The American Physical Society}

Stark broadening of the BIII 2s-2p lines

We present a quantum-mechanical calculation of Stark linewidths from electron-ion collisions for the 2s{sub 1/2}-2p{sub 1/2,3/2}, {lambda}=2066 and 2067 {Angstrom}, resonance transitions in BIII. The results confirm previous quantum-mechanical R-matrix calculations, but contradict recent measurements and semiclassical and some semiempirical calculations. The differences between the calculations can be attributed to the dominance of small L partial waves in the electron-atom scattering, while the large Stark widths inferred from the measurements would be substantially reduced if allowance is made for hydrodynamic turbulence from high-Reynolds-number flows and the associated Doppler broadening. {copyright} {ital 1997} {ital The American Physical Society}

VAMDC--The Virtual Atomic and Molecular Data Centre--A New Way to Disseminate Atomic and Molecular Data--VAMDC Level 1 Release

The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu/) is a European‐Union‐funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a reliable, open, flexible and interoperable e‐science interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. This paper describes the organisation of the project and the achievements during its first year.

Is There a High-Energy Particle Population in the Quiet Solar Corona?

A study of spectra emitted by the quiet solar corona indicates that the majority of line intensities originating in low-lying levels are consistent with isothermal plasma of ~1.3 × 106 K. Nevertheless, a number of line intensities and, in particular, those belonging to ions that are typical of higher temperatures are brighter than expected. We show in this paper that the excess brightness of the hotter lines may be satisfactorily accounted for by a two-Maxwellian electron distribution function. We have calculated the effects on the line intensities and ionization balance under the assumption of both single- and two-Maxwellian electron distribution functions. One Maxwellian is characterized by a temperature of about 110 eV (1.35 × 106 K). The second Maxwellian is assumed to be a high-energy component ranging in temperatures between 150 and 1000 eV, with electron fractions relative to the total electron density that vary from 0.5% to 10%. We found that a good match to the quiet-Sun intensities could be achieved by adding ~5% electrons with a 300-400 eV Maxwellian temperature to the cooler component at 110 eV. We also found that the calculated line intensities become inconsistent with the quiet solar corona measurements if more than 3% of a Te = 500 eV plasma or more than 1% of a Te = 1000 eV plasma is added to the cooler Maxwellian.

Density dependence of the forbidden lines in Ni-like tungsten

The magnetic-octupole (M3) and electric-quadrupole (E2) transitions between the ground state 3d101S0 and the lowest excited 3d94s(5/2, 1/2)J = 3 and J = 2 states in the Ni-like tungsten are shown to exhibit a strong dependence on electron density Ne in the range of values typical for tokamak plasmas. Remarkably, the total intensity of these overlapping lines remains almost constant, which may explain the strong emission in the 7.93 A line observed in tokamak experiments (Neu R et al 1997 J. Phys. B: At. Mol. Opt. Phys. 30 5057). Utilization of the M3 and E2 line ratios for density diagnostics in high-spectral-resolution experiments is discussed as well.

EUV spectral lines of highly-charged Hf, Ta and Au ions observed with an electron beam ion trap

Extreme ultraviolet spectra of highly-charged hafnium, tantalum and gold were produced with an electron beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) and recorded with a flat-field grazing-incidence spectrometer in the wavelength range 4–20 nm. The beam energy was varied between 1.84 and 5.15 keV to selectively enhance spectra from specific ionization stages. Identifications of strong n = 4–n = 4 transitions from Rb-like hafnium (35+) to Co-like gold (52+) were determined with the aid of collisional-radiative modelling of the EBIT plasma. Good quantitative agreement between simulated and measured spectra was achieved. Over 150 spectral lines were identified, 115 of which are new.

QUANTUM-MECHANICAL CALCULATION OF STARK WIDTHS OF NE VII N=3, DELTA N =0 TRANSITIONS

The Stark widths of the Ne VII 2s3s-2s3p singlet and triplet lines are calculated in the impact approximation using quantum-mechanical convergent close-coupling and Coulomb-Born-exchange approximations. It is shown that the contribution from inelastic collisions to the linewidths exceeds the elastic width contribution by about an order of magnitude. Comparison with the linewidths measured in a hot dense plasma of a gas-liner pinch indicates a significant difference which may be naturally explained by nonthermal Doppler effects from persistent implosion velocities or turbulence developed during the pinch implosion. Contributions to the linewidth from different partial waves and types of interactions are discussed as well. @S1050-2947~99!03203-5#