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[en] Dielectronic recombination (DR) in the average-atom (AA) model has been studied. The reasonableness of directly applying the Burgess-Merts (BM) formula to the AA model has been examined. We have noticed that it is inappropriate to use the BM formula to calculate DR rate coefficients for average ions. We have developed a self-consistent-field theoretical method to treat the DR for average ions with electrons. As an example, the DR rate coefficients for argon have been calculated at a defined electron population, and have been compared with the rate-coefficient average via detailed configuration accounting. copyright 1997 The American Physical Society

[en] A systematic derivation of the distribution function of excited ions formed by charge-exchange recombination is presented. The following effects have been taken into account: (1) Finite lifetime of the excited state; (2) energy dependence of the charge-exchange reactivity; (3) nonuniformity of the neutral beam. It is pointed out that the contribution of the terms related to the ion temperature gradient has a different structure compared to the other terms, thereby allowing a direct measurement of the ion temperature gradient. Possible ways for improving the accuracy of electric field measurements are discussed. (c)

[en] A complete treatment of electron-ion recombination of e+FeIII→FeII employing a unified method is presented. The treatment incorporates both the radiative and dielectronic recombinations in a self-consistent manner. Total recombination rate coefficients are obtained from photoionization cross sections, and from collision strengths for dielectronic recombination calculated using the precise theory of Bell and Seaton [J. Phys. B 18, 1589 (1985)]. Large-scale computations for both of these quantities are carried out in the close coupling approximation using the R-matrix method with an eigenfunction expansion that includes 83 states of FeIII dominated by the ground 3d⁶, and the excited 3d⁵4s and 3d⁵4p configurations. Both the total and state-specific recombination rate coefficients are obtained. Comparison of the present results with the previous ones shows considerable difference for most of the temperature regions. The present results provide accurate and self-consistent recombination rates, in the temperature range of practical applications (T<10⁵ K), for ionization balance in photoionization models employing the detailed photoionization cross sections from the Opacity Project. copyright 1997 The American Physical Society

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[en] Two-electron capture with an emission of a single photon (TESP) in collisions of highly charged ions with light atoms is considered. Such a process is actually a time-reversed double photoionization but occurring at specific kinematics. In the lowest order in the interelectron interaction, the TESP probability is determined by two diagrams which are evaluated analytically by means of the Coulomb Green close-quote s function. The calculated ratio of the radiative double-electron capture and single recombination cross sections is in fair agreement with the data obtained in the recent experimental study of this phenomenon. copyright 1997 The American Physical Society

[en] Wave-packet methods involving the numerical solution of the time-dependent Schroedinger equation have been used with great success in the calculation of cross sections for dissociative recombination of molecular ions by electron impact in the high energy region where the ''boomerang'' model [L. Dube and A. Herzenberg, Phys. Rev. A 11, 1314 (1975)] is valid. We extend this method to study low-energy dissociative recombination where this approximation is no longer appropriate. We apply the method to the ''direct'' low-energy dissociative recombination of HD⁺. Our results are in excellent agreement with calculations using the multichannel quantum defect method. (c) 2000 The American Physical Society

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No abstract available

[en] How predictions of deuterium atomic reaction rates in tokamak divertors are altered by changes in cross section data which are comparable with the uncertainty in published data is investigated. An extended neutral diffusion theory calculation, which includes D atoms and ground and excited state D₂ molecules, is performed on a fixed background plasma. For the atoms, the principal relevant mechanisms are elastic scattering, charge exchange, ionization, and recombination. It is evaluated that the charge exchange and electron processes are known to an accuracy better than +/-25%, and it is concluded that this level of accuracy is sufficient for the present state of divertor calculations. Of significant concern is the fact that classical elastic cross sections which are widely used in divertor calculations differ substantially from a more accurate set of cross sections based on quantum mechanics, and that the latter produce predictions of neutral density and ionization rate which differ by orders of magnitude from predictions based on the classical cross sections. Opacity of the plasma to Lyman alpha radiation influences transport for high density plasma situations. The explicit representation of incident particles recycling as molecules is shown to significantly affect the neutral atom density and reaction rates near the divertor plate. In particular, the dissociation of even a small fraction of excited molecules significantly reduces the plasma ion population and increases the neutral atom population just in front of the plate in nearly detached plasmas. copyright 1997 American Institute of Physics