Energy levels and radiative rates for transitions in Ar XIII, Ar XIV and Ar XV

Energies for 524 levels of Ar XIII, 460 levels of Ar XIV and 156 levels of Ar XV have been calculated using the GRASP code of Dyall et al. (1989). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 1%, whereas results for other parameters are probably accurate to better than 20%. Additionally, the level lifetimes derived from our radiative rates are in excellent agreement with measured values.

Energy levels and radiative rates for Li-like Ar XVI and Fe XXIV

Energy levels for transitions among the lowest 24 fine- structure levels belonging to the 1s(2)nl(n greater than or equal to 5) configurations of Li-like Ar XVI and Fe XXIV have been calculated using the fully relativistic GRASP code. Oscillator strengths, radiative rates and line strengths have also been generated among these levels for the four types of transitions: electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2). Comparisons are made for the electric dipole transitions with other available results, and the accuracy of the present data is assessed.

Ionization from the outer shell of Ar by proton impact

Recent results for proton-argon total ionization cross sections [Kirchner Phys. Rev. Lett. 79, 1658 (1997)] show large disagreement between theory and experiment for energies below 80 keV. To address this problem we have employed a recently developed theoretical method with a more pragmatic approach to the charge screening both in the initial and final channels. The target is considered as a one-electron atom and the interactions between this active electron and remaining target electrons are treated by a model potential including both short- and long-range effects. In the final channel the usual product of two continuum distorted wave functions each associated with a distinct electron-nucleus interaction is used. New results in the present calculation show good agreement in total cross sections for the energy range 10-300 keV with the measurement of Rudd [Rev. Mod. Phys. 57, 965 (1985)].

Angular distribution for the elastic scattering of electrons from Ar+(3s^2 3p^5 ^2P) above the first inelastic threshold

The measured angular differential cross section (DCS) for the elastic scattering of electrons from Ar+(3s2 3p5 2P) at the collision energy of 16 eV is presented. By solving the Hartree-Fock equations, we calculate the corresponding theoretical DCS including the coupling between the orbital angular momenta and spin of the incident electron and those of the target ion and also relaxation effects. Since the collision energy is above one inelastic threshold for the transition 3s2 3p5 2P–3s 3p6 2S, we consider the effects on the DCS of inelastic absorption processes and elastic resonances. The measurements deviate significantly from the Rutherford cross section over the full angular range observed, especially in the region of a deep minimum centered at approximately 75°. Our theory and an uncoupled, unrelaxed method using a local, spherically symmetric potential by Manson [Phys. Rev. 182, 97 (1969)] both reproduce the overall shape of the measured DCS, although the coupled Hartree-Fock approach describes the depth of the minimum more accurately. The minimum is shallower in the present theory owing to our lower average value for the d-wave non-Coulomb phase shift s2, which is due to the high sensitivity of s2 to the different scattering potentials used in the two models. The present measurements and calculations therefore show the importance of including coupling and relaxation effects when accurately modeling electron-ion collisions. The phase shifts obtained by fitting to the measurements are compared with the values of Manson and the present method.

Diagnostic studies of species concentrations in a capacitively coupled RF plasma containing CH4-H2-Ar

Three plasma diagnostic methods, tunable infrared diode laser absorption spectroscopy, optical emission spectroscopy and microwave interferometry have been used to monitor concentrations of transient and stable molecules, CH3, CH4, C2H2, C2H6, and of electrons in capacitively coupled CH4-H-2-Ar radiofrequency (RF) plasmas (f(RF) = 13.56 MHz, p = 100 Pa, phi (total)= 66 sccm) for various discharge power values (P = 10-100 W) and gas mixtures. The degree of dissociation of the methane precursor varied between 3% and 60%. The methyl radical concentration was found to be in the order of 10(12) molecules cm(-3) and the electron concentration in the order of loll cm(-3). The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons, C2H2 and C2H6, produced in the plasma, increased with discharge power. The fragmentation rates of the methane precursor and conversion rates to the measured C-2 hydrocarbons were estimated in dependence on discharge power. Radial distributions of the electron and methyl radical concentrations, and of the gas temperature were measured for the first time simultaneously in the plasma region between the discharge electrodes. The measurements allow us to draw qualitative conclusions on the main chemical processes and the plasma chemical reaction paths.

Radiative rates and electron impact excitation rates for H-like Ar XVIII

Aims. In this paper we report on calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for
transitions among the lowest 25 levels of the n ≤ 5 configurations of H-like Ar xviii.
Methods. The general-purpose relativistic atomic structure package (grasp) andDirac atomic R-matrix code (darc) are adopted for
the calculations.
Results. Radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric
quadrupole (E2), and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective
collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 800 Ryd
(107.4 K).

Characterization of a high-density, direct-current reflex discharge plasma source operating in Ar and N-2

The characterization of a direct current, low-pressure, and high-density reflex discharge plasma source operating in argon and in nitrogen, over a range of pressures 1.0-10(-2) mbar, discharge currents 20-200 mA, and magnetic fields 0-120 G, and its parametric characterization is presented. Both external parameters, such as the breakdown potential and the discharge voltage-current characteristic, and internal parameters, like the charge carrier's temperature and density, plasma potential, floating potential, and electron energy distribution function, were measured. The electron energy distribution functions are bi-Maxwellian, but some structure is observed in these functions in nitrogen plasmas. There is experimental evidence for the existence of three groups of electrons within this reflex discharge plasma. Due to the enhanced hollow cathode effect by the magnetic trapping of electrons, the density of the cold group of electrons is as high as 10(18) m(-3), and the temperature is as low as a few tenths of an electron volt. The bulk plasma density scales with the dissipated power. Another important feature of this reflex plasma source is its high degree of uniformity, while the discharge bulk region is free of electric field. (C) 2002 American Institute of Physics.

Stokes imaging, Doppler mapping and Roche tomography of the AM Herculis system V834 Cen

We report on new simultaneous phase-resolved spectroscopic and polarimetric observations of the polar (AM Herculis star) V834 Cen during a high state of accretion. Strong emission lines and high levels of variable circular and linear polarization are observed over the orbital period. The polarization data are modelled using the Stokes imaging technique of Potter et al. The spectroscopic emission lines are investigated using the Doppler tomography technique of Marsh and Horne and the Roche tomography technique of Dhillon and Watson. Up to now, all three techniques have been used separately to investigate the geometry and accretion dynamics in cataclysmic variables. For the first time, we apply all three techniques to simultaneous data for a single system. This allows us to compare and test each of the techniques against each other and hence to derive a better understanding of the geometry, dynamics and system parameters of V834 Cen.