Electron-impact ionization of atomic ions in the W isonuclear sequence

Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of W q+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided.

Section: Electron-impact Ionizationmentioning

confidence: 99%

Fusion-Related Ionization and Recombination Data for Tungsten Ions in Low to Moderately High Charge States

Müller

2015

“…The majority of these spectra have been identified and assigned to nf → 3d (n = 4, 5, 6) and 4d → 3p atomic transitions mostly by performing fully-relativistic ab initio calculations [22][23][24][25]. Besides atomic structure and spectra, the dynamical processes of tungsten ions were also investigated for the purpose of X-ray diagnostics and simulation, such as electron-impact ionization [26], electron-impact excitation [27,28] and dielectronic recombination [29]. However, to the best of our knowledge, there are few work about the linear polarization of tungsten X-ray emissions in ITER fusion plasmas.…”

Section: Introductionmentioning

confidence: 99%

Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions

et al. 2015

Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac-Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W 37+ to W 46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.

“…The calculation time for orders of magnitude is less than other numerical codes because the code TFATOM deals with is comprised of calculations of single or double integrals from the known Thomas-Fermi functions only. The results of comparison of the TFATOM code data for the electron impact ionization cross-sections with available series of experimental data [21][22][23][24][25][26] and the code CADW data [23,26] [21]; open triangles- [22]; full triangles-CADW data [23]; open circles [24]; full squares- [25]; dashed curves signed CADW- [26].…”

Section: Ionization Cross-section and Ratesmentioning

confidence: 99%

Tungsten Ions in Plasmas: Statistical Theory of Radiative-Collisional Processes

Demura

Kadomtsev

Lisitsa

et al. 2015

Abstract:The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. The excitation or ionization of atomic electrons by plasma electron impacts are represented as photo-processes under the action of flux of equivalent photons introduced by E. Fermi. The total electron impact single ionization cross-sections of ions W k+ with respective rates have been calculated and compared with the available experimental and modeling data (e.g., CADW). Plasma radiative losses on tungsten impurity were also calculated in a wide range of electron temperatures 1 eV-20 keV. The numerical code TFATOM was developed for calculations of radiative-collisional processes involving tungsten ions. The needed computational resources for TFATOM code are orders of magnitudes less than for the other conventional numerical codes. The transition from corona to Boltzmann limit was investigated in detail. The results of statistical approach have been tested by comparison with the vast experimental and conventional code data for a set of ions W k+ . It is shown that the universal statistical model accuracy for the ionization cross-sections and radiation OPEN ACCESSAtoms 2015, 3 163 losses is within the data scattering of significantly more complex quantum numerical codes, using different approximations for the calculation of atomic structure and the electronic cross-sections.