ATOMIC AND MOLECULAR DATA AND THEIR APPLICATIONS: Joint Meeting of 14th Internat. Toki Conf. on Plasma Physics and Controlled Nuclear Fusion (ITC14); and 4th Internat. Conf. on Atomic and Molecular Data and Their Applications (ICAMDATA2004)
771(2005); http://dx.doi.org/10.1063/1.1944687View Description Hide Description
Plasma edge physics (plasmas with temperatures in the 1 to 100 eV range, near solid surfaces) has become a key issue in controlled nuclear fusion research. As for the physics of the fully ionized hot plasma core, appropriate dimensionless parameters have been identified: present fusion research acts like wind‐channel experiments on downsized models, with respect to future fusion reactors. This is not longer possible for the plasma edge region due to dominant effects from atomic and surface processes. Integrated computational models comprising the physics of the plasma flow near boundaries, the atomic and molecular processes and the particle‐surface interactions are the only tool to evaluate present experimental results (LHD, JT60, Tore Supra, JET,…) with respect to their relevance for future fusion power experiments (ITER) or a reactor.
In particular proton and electron collisions with the hydrogenic molecules H2, O2, T2, DT, and their ions, play a key role in cooling and attenuating the magnetically confined plasma, before it hits exposed target surfaces. The surface released molecules travel in a bath of electrons and hydrogenic ions, with plasma temperatures (in the relevant region) in the 1 to 20 eV range, and typical (plasma) scale lengths are in the 1 to 10 cm range.
Sample calculations with current fusion plasma edge codes, as e.g. used by the international design team for the ITER prototypical fusion reactor, applied to the tokamak with the highest divertor collisionality today (Alcator‐C‐Mod), are used to demonstrate these issues.
771(2005); http://dx.doi.org/10.1063/1.1944688View Description Hide Description
The Tracer‐Encapsulated Solid PELlet (TESPEL) injection is one of the simplest new ideas to study the impurity confinement and other plasma properties. The special features of this method are: (a) local deposition inside the plasma, (b) precise knowledge of the deposited tracer amount, (c) wide selection of tracer materials. The achievements of the multi‐functional diagnostics using TESPEL injection on LHD are to measure: (a) impurity transport properties, (b) heat diffusivity, (c) particle flow features in and out of the magnetic island, and (d) fast neutral particle fluxes.
771(2005); http://dx.doi.org/10.1063/1.1944689View Description Hide Description
The presence of molecules in the cold scrape‐off layer of fusion experiments and industrial plasmas requires an understanding of the molecular dynamics in these low temperature plasmas. Suitable diagnostic methods can provide an insight in molecular processes in the plasma volume as well as for plasma surface interactions. A very simple but powerful technique is the molecular emission spectroscopy. Spectra are obtained easily, whereas interpretation might be very complex and relies on the availability of atomic and molecular data. Examples are given for hydrogen plasmas and plasmas with hydrocarbons which both are of importance in industrial applications as well as in fusion experiments.
771(2005); http://dx.doi.org/10.1063/1.1944690View Description Hide Description
Plasma Polarization Spectroscopy (PPS) has been applied to a helium plasma produced by ECR heating in a cusp‐configuration magnetic field. Several neutral helium lines are found linearly polarized. The directions of polarization are perpendicular to the magnetic fields, and the polarization degrees are from several to more than ten percent. From the observed intensity and polarization degree, we deduce the population and alignment of the upper levels of these lines. The Population‐Alignment Collisional‐Radiative model is constructed, and the observed results are interpreted in terms of an anisotropic velocity distribution of electrons. The distribution is found to be of a Saturn‐type with, for example, the central component with temperature 14 eV and the ring component of 40% electrons displaced by 9.2 eV having the same temperature. Differences in the calculated populations and alignments for different cross section data are discussed.
771(2005); http://dx.doi.org/10.1063/1.1944691View Description Hide Description
The analysis of equilibrium conditions might be irrelevant to determine the importance of a certain set of atomic data. We show, that in non‐equilibrium and optically thick plasmas intercombination transitions between highly excited states as well as higher order dielectronic satellite transitions are of extraordinary importance for diagnostics. In optically thin equilibrium plasmas, however, they are almost negligible. Numerical examples are presented for neutral helium in attached/detached plasmas as well as for dense laser produced plasmas.
771(2005); http://dx.doi.org/10.1063/1.1944692View Description Hide Description
High‐resolution X‐ray spectroscopy of Active Galactic Nuclei has become possible thanks to the launch of XMM‐Newton and Chandra with their grating spectrometers, and will be explored further after the expected launch of ASTRO‐E2 with its XRS detector. In several AGN the X‐ray spectra show the signatures of on outflowing, photo‐ionised wind. Also several X‐ray binaries show a similar imprint of a photo‐ionised gas. The clearest signatures are formed by the broad range of absorption lines, mostly from the ground states of a wide range of ionisation states of the abundant elements. In addition to absorption lines due to the valence electrons, the spectra show many inner‐shell absorption lines. Examples are the K‐shell transitions of the most abundant metal, oxygen, in the 19–23 Å band, and 2p‐3d transitions of lowly ionised iron in the 15–17 Å region. These transitions have an extremely important diagnostic value, as other transitions of the same ions frequently occur in the unobservable extreme ultraviolet. Several of these inner‐shell transitions, however, lack accurate experimental or theoretical wavelengths, which makes the spectral analysis complicated and ambiguous. This is even more the case for transitions from metastable levels, which can be used as density diagnostics. Finally, attention is payed to the role of atomic data in the photo‐ionisation equilibrium calculations. Uncertainties in for example dielectronic recombination rates cause large uncertainties in the predicted absorption line strengths.
771(2005); http://dx.doi.org/10.1063/1.1944693View Description Hide Description
The R‐Matrix method has long been employed to compute fundamental atomic parameters with high precision for large scale applications to astrophysical sources and magnetic and intertial fusion devices. Ongoing work is part of two projects: The Iron Project that focuses on Fe‐peak elements, and the RmaX Project aimed at spectral diagnostics of laboratory and astrophysical X‐ray plasmas. The primary atomic processes include electron impact excitation, photoionization, (e + ion) recombination, and spectral transitions. These data are employed in numerical simulations of high‐temperature plasmas under stationary and transient conditions. The calculated paraemeters have been benchmarked against sophisticated experiments on electron‐beam‐ion‐traps for excitation, synchrotron based light sources for photoionization, and heavy ion storage rings for (e + ion) recombination. Extensions of the two projects include a self‐consistent and unified theoretical treatment of (e + ion) recombination that subsumes both the radiative and the dielectronic recombination processes. Cross sections are computed using an identical (e + ion) wavefunction expansion for both the photoionization and the recombination processes, thereby considering the resonant and non‐resonant phenomena in an ab initio manner. Comparison with experiments ascertain an accuracy of 10–20%, within the uncertainties in experiment and theory, indicating that there are no significant shortcomings in the R‐matrix method. We compare the close coupling R‐matrix data with the Distorted Wave approximation and the effect on X‐ray spectral analysis. Finally, we describe the electronic database TIPTOPbase, which will also make available new stellar opacities and radiative accelerations from the Opacity Project.
771(2005); http://dx.doi.org/10.1063/1.1944694View Description Hide Description
The present paper prepresents an attempt to summarize the different data needs in the context of interstellar space. The availability of future high spectral and angular resolution instruments reinforces the requirement of skilled data bases in a variety od domains. In addition to spectroscopic databases, chemical kinetics data involving ion‐molecule, neutral‐neutral reaction, dissociative recombination, photodissociation and photoionization cross sections are mentioned. We also refer to inelastic collision rate coefficients where atomic and molecular Hydrogen, Helium stand as perturbers. Finally we put forward the involvement of atomic and molecular databases into the efforts addressed by the perspective of International Virtual Observatories.
771(2005); http://dx.doi.org/10.1063/1.1944695View Description Hide Description
Recent chemical abundance studies, especially measurements of isotope abundance ratios, for very metal‐deficient stars have provided important constraints on models of individual nucleosynthesis processes. Measurements of isotope abundances, as well as elemental abundances, from stellar spectra are briefly reviewed. Recent studies of Eu isotope ratios in metal‐deficient stars, and the application to the analysis of an s‐process branching are discussed.
771(2005); http://dx.doi.org/10.1063/1.1944696View Description Hide Description
Recent measurements of low energy, absolute electron scattering cross sections for vibrational excitation of NO have been used to update the cross set used for modeling atmospheric auroral processes. These new cross sections, which highlight the role that intermediate negative ions (resonances) play at energies below 5 eV in mediating vibrational excitation, also indicate that electron‐driven processes play an important role in the infrared (∼5 um) auroral emissions from the NO molecule.
771(2005); http://dx.doi.org/10.1063/1.1944697View Description Hide Description
Lightning discharge temporarily produces strong electric field in the middle and upper atmosphere, which accelerates ambient electrons and causes optical emission called sprites through the electron collisions with neutrals (e.g., N2, O2, and O). The electron collisions dominant in the phenomena also generate metastable species initiating chemical reactions. For numerical study, we use (1) the cross section data of electron‐neutral collisions to calculate the electron energy distributions in sprites and (2) the Einstein and quenching coefficients to calculate the intensity of optical emissions. Finally, it is pointed out that the uncertainty of cross section data used in the sprite study is the most critical problem for the correct estimation of chemical effects of sprite events.
771(2005); http://dx.doi.org/10.1063/1.1944698View Description Hide Description
Currently the emission of both Xe and Sn are being investigated as sources for EUV lithography. In Xe the bulk of the emission in the region of interest, 13.5 nm, originates from one ion stage, Xe XI, while in Sn, the emission at this wavelength arises from resonance transitions in a range of stages and thus is potentially more intense. However essentially no data for these ions exists making modeling of the plasma processes involved and estimation of the conversion efficiencies attainable and their dependence on experimental parameters extremely difficult. Here we provide an overview of some recent results obtained by our group and compare them with data from other researchers.
771(2005); http://dx.doi.org/10.1063/1.1944699View Description Hide Description
Processing plasmas often produce clusters, ranging in size from a few nanometer up to micrometers. Due to their negative charge, clusters are confined by the sheath electric fields until their mass enables gravity to pull them out of the discharge. Examples are discharges in SiH4 or C2H2. Although there is agreement on the global aspects of the chemistry, details on many processes are lacking. This concerns attachment of electrons to large molecules, restructuring leading to a reduction of the hydrogen content, and the interaction between large negative ions and (excited) molecules, radicals, and positive ions of the parent gas. Results from a one‐dimensional model for a radio‐frequency discharge in SiH4/H2 will be used to illustrate the consequences of various assumptions regarding these basic steps in the chemistry.
For discharges in mixtures containing hydrocarbons the incorporation of C2 groups in polycyclic aromatic hydrocarbons has been proposed as an additional mechanism for dust formation. This is the main process adopted in astrophysics. Also in Tokamaks the formation of carbonaceous dust is observed, caused mostly by the erosion of carbon containing divertor tiles and redeposited layers on plasma facing components. In case of detached operation the plasma in the divertor will be similar to that of a processing discharge, favoring homogeneous processes. In ITER this will be accompanied by hydrogen ion fluxes up to 1024 m−2s−1 and power fluxes up to 10 MWm−2, leading to evaporation of wall material. Here we will discuss the chemistry in these situations (processing discharges and divertors), indicating open questions regarding cluster formation.
Secondary Electrons from Water Vapor with the Impact of 6.0 MeV/u He2+ Ions: Atomic Data and their Application to Biomedical Investigations771(2005); http://dx.doi.org/10.1063/1.1944700View Description Hide Description
We measured the energy and angular distributions (7 eV–10 keV and 20°–160°) of secondary electrons produced in collisions of 6.0 MeV/u He2+ ions with water vapor. Binary‐encounter collision peaks were clearly observed at the calculated energies at angles of <90°, as well as the K‐LL Auger peak of oxygen at about 500 eV for all angles. From these measurements, the doubly differential cross sections (DDCS) of electron emissions were deduced with an estimated uncertainty of ±13%. The energy distribution (SDCS) was also obtained by integrating the DDCS values with respect to the ejected angles, and compared with an empirical model of Rudd. The energy spectrum (SDCS) showed good agreement with the model of Rudd in the energy range of secondary electrons of <100 eV. However, in the 100–1000 eV energy range, the experimental spectrum shows significant discrepancies, smaller by 30%, and is nearly twice greater in the region >3keV. To assess the new cross sections, these values were incorporated in the kurbuc Monte‐Carlo track structure code system for a simulation of secondary electrons. Radial dose distributions for 6.0 MeV/u He2+ ions were obtained by analyzing the tracks generated by the code kurbuc using the new DDCS values. In the core with a radius (r) of less than 1 nm, the dose is very high due mainly to excitation events, induced by low‐energy electrons. The penumbra shows a well‐known r −2 dependence.
771(2005); http://dx.doi.org/10.1063/1.1944701View Description Hide Description
During the past years, the RATIP program has been found useful for calculating a variety of atomic data, including level structures, transition probabilities, Auger parameters as well as a number of excitation, ionization and capture cross sections. Here, the recent extensions to the RATIP code are reviewed which help analyze and explain many experiments from atomic spectroscopy.
771(2005); http://dx.doi.org/10.1063/1.1944702View Description Hide Description
The spectra of neutral and ionized rare earth elements have been receiving renewed attention from laboratory spectroscopists during recent years. These efforts have been motivated by data needs of the astrophysics and lighting research communities. In astrophysics studies of metal‐poor Galactic halo stars are providing a deeper understanding of the origins of heavy elements, of the chemical evolution of the Galaxy, and some insights into the rapid and slow neutron‐capture mechanisms. Rare earth elements are widely used in Metal Halide High Intensity Discharge lamps. The superior performance of such lamps has motivated further development of these devices. Basic spectroscopic data are needed for modeling and diagnosing new lamp designs. This paper reviews progress on determining atomic transition probabilities for neutral and singly ionized rare elements. The most widely used experimental method involves combining radiative lifetimes from laser induced fluorescence measurements, with emission branching fractions from Fourier transform spectra. Theoretical methods for determining atomic transition probabilities have also been improved in recent years. Progress on hyperfine structure and isotopic data is also discussed in this paper.
771(2005); http://dx.doi.org/10.1063/1.1944703View Description Hide Description
This paper reviews the most recent experimental studies of absolute cross sections for electron‐impact excitation of atomic and dissociative excitation of molecular ions. Experimental studies of such processes have been carried out for more than 40 years. Much of the discussion is oriented to the work involving the author; however an effort will be made to include other results. In discussing electron impact excitation of atomic ions we will examine primarily transitions in which dielectronic resonaces play a dominant role, and measurements which can be used to benchmark results of theoretical calculations. Of particular interest, partially motivated by fusion efforts and partially by plasma etching and deposition, are investigations of dissociative excitation of light hydrocarbon ions. Methods employing colliding beams of electrons and ions, either in crossed or merged beams configurations are emphasized.
771(2005); http://dx.doi.org/10.1063/1.1944704View Description Hide Description
Recent experimental measurements of cross sections for electron‐impact ionization of atomic and molecular ions will be highlighted, with emphasis on results obtained with the crossed‐beams method. These accurate absolute cross sections and high‐resolution energy scans for atomic ions provide valuable benchmarks for theoretical efforts on direct and indirect ionization of these ions. Experimental data on ionization of molecular ions should motivate more theoretical interest in these more complex systems.
771(2005); http://dx.doi.org/10.1063/1.1944705View Description Hide Description
The focus of this article is on the measurement of product branching ratios in the dissociative recombination of polyatomic molecular ions with electrons by means of ion storage rings. Recombination of ions of interest in astrophysics, plasma‐assisted combustion, thermonuclear fusion, protein fragmentation, and atmospheric physics are reviewed and discussed.