The ionization fraction is a key figure of merit for optimizing the performance of plasma device. This work presents an optical emission spectroscopy (OES) method to determine the ionization fraction in lowtemperature xenon plasma. The emission lineratio of xenon ionic and atomic 6
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to nonfederal websites. Their policies may differ from this site.

Abstract p –6s transitions is used in this method. A comprehensive collisionalradiative model developed in our previous work is employed to describe the relationship between the lineratios and the plasma parameters. It is found that some special lineratios have a sensitive relationship to the ionization fraction, e.g. the ratio of the 460.30 nm line and 828.01 nm lines. These lineratios are selected for the diagnostic method. The method is demonstrated in a magnetized discharge chamber. The axiallyresolved emission spectra of the ionization chamber are measured, and from those the ionization fraction along the chamber axis is determined via the OES method. The axiallyresolved ionization fraction is found to be dependent on the magnetic field and agrees well with those obtained from a Langmuir probe. In the experiment, the probe is overheated under some conditions, possibly due to the bombardment by energetic particles. In this case, no results can be obtained from the probe, while the OES method can still obtain reasonable results. Combined with optical tomography and spectral imaging technology, the OES method can also provide the spatial distribution of the ionization fraction, which is needed for revealing the discharge mechanisms of plasma devices.Free, publiclyaccessible full text available September 1, 2024 
Abstract We report on a series of detailed BreitPauli and Dirac Bspline Rmatrix (DBSR) differential cross section (DCS) calculations for excitation of the
and$$5\,^2\textrm{S}_{1/2} \rightarrow 5\,^2\textrm{P}_{1/2}$$ $5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{S}}_{1/2}\to 5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{P}}_{1/2}$ states in rubidium by 40 eV incident electrons. The early BP computations shown here were carried out with both 5 states and 12 states, while the DBSR models coupled 150 and 325 states, respectively. We also report corresponding results from a limited set of DCS measurements on the unresolved$$5\,^2\textrm{S}_{1/2}\rightarrow 5\,^2\textrm{P}_{3/2}$$ $5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{S}}_{1/2}\to 5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{P}}_{3/2}$ states, with the experimental data being restricted to the scattered electron angular range 2–$$5\,^2\textrm{P}_{1/2,3/2}$$ $5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{P}}_{1/2,3/2}$ . Typically, good agreement is found between our calculated and measured DCS for excitation of the unresolved$$10^\circ $$ ${10}^{\circ}$ states, with best accord being found between the DBSR predictions and the measured data. The present theoretical and experimental results are also compared with predictions from earlier 40 eV calculations using the nonrelativistic DistortedWave Born Approximation and a Relativistic DistortedWave model.$$5\,^2\textrm{P}_{1/2,3/2}$$ $5{\phantom{\rule{0ex}{0ex}}}^{2}{\text{P}}_{1/2,3/2}$Graphic abstract 
Within the framework of the improved quantitative rescattering (QRS) model, we simulate the correlated twoelectron momentum distributions (CMDs) for nonsequential double ionization (NSDI) of Ar by elliptically polarized laser pulses with a wavelength of 788 nm at an intensity of 0.7 × 10^{14}W/cm^{2}for the ellipticities ranging from 0 to 0.3. Only the CMDs for recollision excitation with subsequent ionization (RESI) are calculated and the contribution from recollision direct ionization is neglected. According to the QRS model, the CMD for RESI can be factorized as a product of the parallel momentum distribution (PMD) for the first released electron after recollision and the PMD for the second electron ionized from an excited state of the parent ion. The PMD for the first electron is obtained from the laserfree differential cross sections for electron impact excitation of Ar^{+}calculated using stateoftheart manyelectron
R matrix theory while that for the second electron is evaluated by solving the timedependent Schrödinger equation. The results show that the CMDs for all the ellipticities considered here exhibit distinct anticorrelated backtoback emission of the electrons along the major polarization direction, and the anticorrelation is more pronounced with increasing ellipticity. It is found that anticorrelation is attributed to the pattern of the PMD for the second electron ionized from the excited state that, in turn, is caused by the delayed recollision time with respect to the instant of the external field crossing. Our work shows that both the ionization potential of the excited parent ion and the laser intensity play important roles in the process. 
Since its initial development in the 1970s by Phil Burke and his collaborators, the Rmatrix theory and associated computer codes have become the method of choice for the calculation of accurate data for general electron–atom/ion/molecule collision and photoionization processes. The use of a nonorthogonal set of orbitals based on Bsplines, now called the Bspline Rmatrix (BSR) approach, was pioneered by Zatsarinny. It has considerably extended the flexibility of the approach and improved particularly the treatment of complex manyelectron atomic and ionic targets, for which accurate data are needed in many modelling applications for processes involving lowtemperature plasmas. Both the original Rmatrix approach and the BSR method have been extended to the interaction of short, intense electromagnetic (EM) radiation with atoms and molecules. Here, we provide an overview of the theoretical tools that were required to facilitate the extension of the theory to the time domain. As an example of a practical application, we show results for twophoton ionization of argon by intense shortpulse extreme ultraviolet radiation.more » « less

Cross sections for electron scattering from atomic and molecular iodine are calculated based on the Rmatrix (closecoupling) method. Elastic and electronic excitation cross sections are presented for both I and I2. The dissociative electron attachment and vibrational excitation cross sections of the iodine molecule are obtained using the local complex potential approximation. Ionization cross sections are also computed for I2 using the BEB model.more » « less

We reinvestigate a key process in electronatom collision physics, the elastic scattering of electrons from helium atoms. Specifically, results from a specialpurpose relativistic polarizedorbital method, which is designed to treat elastic scattering only, are compared with those from a very extensive, fully ab initio, generalpurpose Bspline Rmatrix (closecoupling) code.more » « less

The Dirac Bspline Rmatrix (DBSR) method is employed to treat lowenergy electron collisions with thallium atoms. Special emphasis is placed on spin polarization phenomena that are investigated through calculations of the differential crosssection and the spin asymmetry function. Overall, good agreement between the present calculations and the available experimental measurements is found. The contributions of electron exchange to the spin asymmetry cannot be ignored at low impact energies, while the spin–orbit interaction plays an increasingly significant role as the impact energy rises.more » « less

Benchmark intensity ratio measurements of the energy loss lines of krypton for excitation of the 4p61S0→4p55s[3/2]2, 4p55s[3/2]1, 4p55s′[1/2]0, and 4p55s′[1/2]1 transitions are reported, these being the lowest electronic excitations for krypton. The importance of these ratios as stringent tests of theoretical electron scattering models for the noble gases is discussed, as well as the role of spinexchange and direct processes regarding the angular dependence of these ratios. The experimental data are compared with predictions from fullyrelativistic Bspline Rmatrix (closecoupling) calculations.more » « less