Proton Impact Excitation Research Articles

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

Proton impact charge exchange and excitation cross sections for liquid Sn divertor studies

AbstractThe quantum dynamics of charge exchange (electron capture) and excitation processes in proton collisions with Sn atoms is studied for the first time by using the two‐centre atomic orbital close coupling method. The expansion basis includes the lowest nine states of singlet and triplet symmetry of Sn and all the states with n ≤ 8 of the H atom. The spin‐resolved state‐selective charge exchange (up to n = 5) and excitation cross sections are calculated in the energy range of 0.5 − 100 keV. Strong coupling between the electron capture and excitation channels is observed in the low‐energy (E ≤ 10 keV) region associated with the energy quasi‐resonance of some projectile and target states. The intensities of some strong Sn spectral lines are also calculated for a number of typical tokamak edge plasma temperatures.

Electron- and proton-impact excitation of heliumlike uranium in relativistic collisions

We have studied the K-shell excitation of He-like uranium (U90+) in relativistic collisions with hydrogen and argon atoms. Performing measurements with different targets, as well as with different ...

Proton impact excitation of the Na atom

A time-dependent close-coupling (TDCC) method is developed and used to calculate proton impact excitation cross sections for atoms. Cross sections for excitations of the Na atom are calculated for proton impact energies ranging from 1.0 to 100.0 keV. The TDCC cross sections are found to be in agreement for some energies with recommended cross sections from overall fits to theoretical and experimental atomic data.

Relativistic proton-impact excitation of hydrogen atom in the presence of intense laser field

A theoretical treatment, using the first Born approximation, is presented to analyse the results of relativistic laser-assisted proton – hydrogen atom scattering. Specific calculations are carried out for excitation of hydrogen atoms from 1s1/2 to 2s1/2 states by proton impact. We work in an approximation in which the incoming proton may be described by Dirac–Volkov states in the presence of a laser field. Semi-relativistic Darwin wave functions are used to describe the hydrogen atom in its initial and final states, while relativistic, spin, and laser interaction effects are also accounted for. The results presented in this paper show that the differential cross section for this process depends not only upon the energy of the incident proton, but also upon its interaction with the laser field through intensity and frequency.

Electron- and proton-impact excitation of He-like uranium

SynopsisIn this contribution, we present an experimental and theoretical study of the proton- and electron- impact excitation effects in helium-like uranium ions in relativistic collisions with different gaseous targets. The experiment was carried out at the experimental storage ring at GSI Darmstadt. Our experimental results are in agreement with predictions of the state-of-the art theory which treats both processes within the relativistic framework.

Ground-state excitation of heavy highly-charged ions

We have studied the excitation of H-like and He-like uranium (U91+ and U90+) in relativistic collisions with gaseous targets by observing the subsequent x-ray emission. The experiment was conducted at the ESR storage ring of the GSI accelerator facility in Darmstadt, Germany. The measurements were performed with a newly developed multi-phase target at different collision energies. This enabled us to explore the proton (nucleus) impact excitation as well as the electron impact excitation processes in the relativistic collisions. The large fine-structure splitting in uranium allowed us to unambiguously resolve excitation to different L-shell levels. Moreover, information about the population of different magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The experimental results are compared with calculations performed within the relativistic framework including excitation mechanisms due to both protons (nucleus) and electrons.

General state-to-state transitions in atoms for either Yukawa or Coulomb potentials via Fourier transforms

In a previous paper we used our integro-differential extension of Gaussian transforms to find the closed analytic form for hydrogenic bound-state transitions with arbitrarily high quantum numbers due to projectile impact excitation via Coulomb potentials (in the intermediate representation). Here we extend that result to Yukawa potentials, but do so by utilizing Fourier transforms. The result is used to find the first-order cross section for proton impact excitation of hydrogen to the 2s–7s final states. Because the results hold for any initial and final quantum states, and the amplitude may be easily converted for use with pseudostates, it may be used to automatically calculate sums over intermediate pseudostate propagators whose (bound and free) principal and angular quantum numbers can become very large. This result may be extended to multi-electron transition amplitudes by representing initial and final states by configuration–interaction wave-functions.

Excitation of the n=2 levels of hydrogen by proton impact for hydrogen beam diagnostics

The atomic orbital close coupling approach has been used to compute a comprehensive data set for proton-impact excitation of atomic hydrogen owing to the need for complete data for motional Stark effect spectroscopy of fusion plasmas enabled by neutral beam injection.

Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions

The K shell excitation of H-like uranium (U(91+)) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.

Research on proton-impact excitation process of hydrogen atom in Debye plasma

The high-energy H++H impact excitation process in Debye plasma is investigated using impact parameter Born approximation method. In the cases of several different values of Debye length D, the inter-nuclear distance R of matrix elements, the weighted probability at a collision energy of 160 keV/u, and impact excitation cross sections in an energy range of 100–1000 keV/u for direct 1s → 2p transition in H for both the unscreened and screened Coulomb interactions are calculated. It is demonstrated that the magnitude of impact excitation cross section gradually reduces as screening parameter increases. According to the excitation cross section formula and the calculated results, a detailed analysis of the reason for the reduction caused by excitation cross section is given in this paper. The effects of screened Coulomb interaction on the potential of between incident particles and excited electronic and on the hydrogenatomic structure (wave function and energy level) have very important influence on the excitation cross section.

Electron- and Proton-Impact Excitation in Stored Hydrogenlike Uranium Ions

The projectile excitation of high-Z ions has been investigated in relativistic ion-atoms collisions by observing the subsequent x-ray emission. Within this experiment information about the population of the magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. In addition, we have observed for the first time the effect of electron-impact excitation in a heavy highly charged ion undergoing a collision with a neutral atom.

Non-statistical population distributions for hydrogen beams in fusion plasmas

Most atomic models for neutral hydrogen beams in fusion plasmas assume a statistical (Boltzmann) distribution of populations for excited states with the same principal quantum number n. Here we analyze population distributions for the excited magnetic sublevels of a beam under typical conditions of existing and future fusion devices. The collisional–radiative model NOMAD based on completely m-resolved parabolic states up to n = 10 is used to study this problem. The model utilizes new proton-impact excitation data calculated with the atomic-orbital close-coupling method and the Glauber approximation and takes into account electric-field-induced ionization from highly excited states. Our simulations show that the statistical assumption for a specific n is generally not valid for typical fusion conditions due to radiative processes and strong field ionization. The deviation increases considerably for higher beam energies and stronger magnetic fields. The calculated line intensities of σ and π components and beam-emission parameters are discussed in detail.

Proton-impact excitation of lithium using a time-dependent close-coupling method

A time-dependent close-coupling method, formulated within the framework of a rotational function expansion in two-dimensional cylindrical coordinates, is used to investigate excitation processes in proton-lithium collisions. As a first check, the calculated $\text{Li}(1{s}^{2}2s)\ensuremath{\rightarrow}\text{Li}(1{s}^{2}2p)$ excitation cross sections are compared and shown to be in reasonable agreement with the previous Cartesian lattice time-dependent Schr\"odinger equation results for collision energies at 5, 10, and 15 keV. As a result, additional calculations are carried out to determine the cross sections not only for the $\text{Li}(1{s}^{2}2s)\ensuremath{\rightarrow}\text{Li}(1{s}^{2}2p)$ transitions, but also for the Li($1{s}^{2}3l$) transitions for a wider range of proton-impact energies from 2 to 50 keV. Reasonable agreement is found when further comparison of the dominant Li($1{s}^{2}2p$) excitation cross sections is made with data obtained from crossed-beams experiments and other close-coupling methods. With the present extensive and large-scale calculations, the convergence for the reported results is also addressed, especially for the less-dominant Li($1{s}^{2}3l$) transitions, with respect to the box sizes, number of coupled channels, and propagation time.

Electron density dependence of intensity ratio for FeXXII extreme ultraviolet emission lines arising from different ground levels in electron beam ion trap and large helical device

Extreme ultraviolet (EUV) spectra of highly charged iron ions in a wavelength range of 100–300 Å have been observed from two different plasma sources of the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) with a monoenergetic electron beam and a Large Helical Device (LHD) with Maxwellian electron energy. The excitation process of the spectral lines is compared between the two plasmas, and it is found that the excitation process for Fe XIX - Fe XXII ions is clearly different. Namely, the EUV emission lines from the EBIT plasma are only dominated by electron impact excitation connected to the ground state, but the excitation mechanism is not so simple in the LHD plasma. The difference in the excitation process is studied by measuring the intensity ratio of EUV emission lines (114.412 Å [1s22s2p2 2P3/2 → 1s22s22p 2P3/2]/117.144 Å [1s22s2p2 2P1/2 → 1s22s22p 2P1/2]) arising from different ground levels in the Fe XXII ions. The line intensity ratio has an extremely small value of 0.2 in the EBIT plasma with a low beam current of 30 mA and a beam energy of 2 keV, while the ratio varies with the electron density ne in the LHD plasmas, i.e., 0.35 for ne = 1 × 1013 cm−3 and 0.65 for ne = 4 × 1013 cm−3. Here, the electron density of the EBIT plasma is estimated to be smaller than 1012 cm−3 and the electron temperature of the LHD plasmas is 2 keV. The dependence of the line intensity ratio on the observed electron density is analyzed for both the EBIT and the LHD plasmas using several collisional-radiative (CR) models. The present experimental data can easily be reproduced by the analysis when the thermal proton impact excitation is taken into account. The importance of the proton impact excitation is also experimentally verified by injecting an iron pellet into the LHD plasmas and changing the ratio of the proton density to the electron density.

Recommended data on proton-ion collision rate coefficients for Fe X–Fe XXIII ions

Aims. Proton-ion collisions are important for excitation or de-excitation of certain excited states in a high-temperature low density astrophysical plasma. Methods. In the present work an evaluation of data obtained for proton-induced transitions in Fe X–Fe XXIII ions is carried out with the help of different theoretical methods. Results. A simple analytical formula with seven parameters is suggested. This formula allows us to describe the dependence of the proton rate coefficient on the proton temperature in a wide temperature range. The values of the free parameters have been determined by fitting the approximation formula to numerical data and are presented for recommended data together with fitting accuracies. By comparing proton collision rates with electron rates it is shown that proton impact excitation processes may be important for Fe X, XI, XIII–XV, XVII–XXIII ions. The results obtained can be used for plasma kinetics calculations and for the development of spectroscopic methods of astrophysical plasma diagnostics.

Forbidden transitions in excitation by proton impact in Li-like Al ions

This paper presents cross-sections and collision strengths for proton-impact excitation of optically forbidden transitions in Al10+. These data, calculated in the impact-parameter formalism, covering the expected range of energies/temperature in laser-produced plasmas, are believed to represent the first such detailed treatment of this system. The cross-sections decrease with energy as E−1, while the collision strengths tend to finite limits as the energy of colliding proton becomes infinitely great. This high-energy limiting value has been evaluated combining results from the semi-classical treatment of ion-impact excitation processes and the Born approximation for high-energy behavior of the collision strength. The effective target size has been estimated from the calculated high-energy limit of the collision strength in the Born approximation.

Identification and intensity analysis on forbidden magnetic dipole emission lines of highly charged Al, Ar, Ti and Fe ions in LHD

Forbidden lines arising from magnetic dipole (M1) transitions in 2 s 2 2 p x ( x = 1 – 5 ) ground and 2s2p excited configurations of highly charged Al, Ar, Ti and Fe ions have been observed in the large helical device (LHD). Argon was puffed using a piezo-electronic valve and other metallic materials were injected using an impurity pellet injector into LHD plasma for the observation. The M1 transitions in vacuum ultraviolet (VUV) and visible regions are identified by analyzing their Doppler broadening, temporal intensity behavior and spatial intensity distribution. Wavelengths of these M1 transitions are determined with high accuracy and compared with previous experimental and calculated values. The line intensity ratios of the M1 transition to the allowed (E1) transition such as 2 s 2 2 p 5 P 3 / 2 2 – P 1 / 2 2 / 2 s 2 2 p 5 P 3 / 2 2 – 2 s 2 p 6 S 1 / 2 2 (ArX 5533 Å/165 Å, TiXIV 2118 Å/122 Å and FeXVIII 975 Å/94 Å) and 2s2p P 1 3 – P 2 3 / 2 s 2 S 0 1 – 2 s 2 p P 1 1 (ArXV 5944 Å/221 Å) are measured as a function of electron density. Results on the ArX and ArXV are compared with a simple level-population calculation. As a result, the density dependence of the ratio is well explained mainly by a competition between two decay processes of the collisional de-excitation and the radiative decay due to the forbidden line emission, although a clear discrepancy between the experimental and calculated absolute values appears for the ArX ratio. Contribution of fast proton impact excitation, which is brought by 180 keV neutral beam injection (NBI) for plasma heating, is also analyzed with the calculation for the F-like ions of ArX, TiXIV and FeXVIII.

An Assessment of the Fe xviii and Fe xix Line Ratios from the Chandra Grating Observations of Capella

Observations of Fe XVIII and Fe XIX X-ray, extreme-UV, and far-UV line emission, formed at the peak of Capella's (α Aurigae's) emission measure distribution and ubiquitous in spectra of many cool stars and galaxies, provide a unique opportunity to test the robustness of Fe XVIII and Fe XIX spectral models. The Astrophysical Plasma Emission Code (APEC) is used to identify over 35 lines from these two ions alone, and to compare model predictions with spectra obtained with the Chandra Low Energy Transmission Grating and High Energy Transmission Grating Spectrometers, the Far Ultraviolet Spectroscopic Explorer (FUSE), and the Extreme Ultraviolet Explorer. Some flux discrepancies larger than a factor of 2 are found between observations of Fe XVIII and Fe XIX lines and predictions by APEC and other models in common use. In particular, the X-ray resonance lines for both ions are stronger than predicted by all models relative to the EUV resonance lines. The multiwavelength observations demonstrate the importance of including dielectronic recombination and proton-impact excitation, and of using accurate wavelengths in spectral codes. These ions provide important diagnostic tools for 107 K plasmas currently observed with Chandra, XMM-Newton, and FUSE.

Proton-impact excitation of laser-excited lithium atoms

A time-dependent solution of the Schr\"odinger equation on a three-dimensional lattice is used to calculate proton-impact excitation cross sections for both the ground $(2s)$ and first excited $(2p)$ states of the neutral lithium atom. Total cross sections for the $2\stackrel{\ensuremath{\rightarrow}}{s}3l$ and $2\stackrel{\ensuremath{\rightarrow}}{p}3l$ excitations are compared with atomic-orbital close-coupling calculations at incident energies of 15--50 keV. In support of future experiments involving crossed ion, atom, and laser beams, total aligned cross sections for the $2p\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\sigma}}3l$ and $2p\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\pi}}3l$ excitations are presented over the same energy range. The ratio of aligned cross sections for certain excitations and incident energies is found to be almost a factor of 2.