Ion Spectral Lines Research Articles

Laboratory study of collisionless coupling between explosive debris plasma and magnetized ambient plasma

The explosive expansion of a localized plasma cloud into a relatively tenuous, magnetized, ambient plasma characterizes a variety of astrophysical and space phenomena. In these rarified environments, collisionless electromagnetic processes rather than Coulomb collisions typically mediate the transfer of momentum and energy from the expanding “debris” plasma to the surrounding ambient plasma. In an effort to better understand the detailed physics of collisionless coupling mechanisms, compliment in situ measurements of space phenomena, and provide validation of previous computational and theoretical work, the present research jointly utilizes the Large Plasma Device and the Raptor laser facility at the University of California, Los Angeles to study the super-Alfvénic, quasi-perpendicular expansion of laser-produced carbon (C) and hydrogen (H) debris plasma through preformed, magnetized helium (He) ambient plasma via a variety of diagnostics, including emission spectroscopy, wavelength-filtered imaging, and a magnetic flux probe. Doppler shifts detected in a He1+ ion spectral line indicate that the ambient ions initially accelerate transverse to both the debris plasma flow and the background magnetic field. A qualitative analysis in the framework of a “hybrid” plasma model (kinetic ions and inertia-less fluid electrons) demonstrates that the ambient ion trajectories are consistent with the large-scale laminar electric field expected to develop due to the expanding debris. In particular, the transverse ambient ion motion provides direct evidence of Larmor coupling, a collisionless momentum exchange mechanism that has received extensive theoretical and numerical investigation. In order to quantitatively evaluate the observed Doppler shifts, a custom simulation utilizing a detailed model of the laser-produced debris plasma evolution calculates the laminar electric field and computes the initial response of a distribution of ambient test ions. A synthetic Doppler-shifted spectrum constructed from the simulated test ion velocities excellently reproduces the experimental measurements, verifying that the observed ambient ion motion corresponds to collisionless coupling through the laminar electric field.

Stark broadening measurements in plasmas produced by laser ablation of hydrogen containing compounds

We present a method for the measurement of Stark broadening parameters of atomic and ionic spectral lines based on laser ablation of hydrogen containing compounds. Therefore, plume emission spectra, recorded with an echelle spectrometer coupled to a gated detector, were compared to the spectral radiance of a plasma in local thermal equilibrium. Producing material ablation with ultraviolet nanosecond laser pulses in argon at near atmospheric pressure, the recordings take advantage of the spatially uniform distributions of electron density and temperature within the ablated vapor. By changing the delay between laser pulse and detector gate, the electron density could be varied by more than two orders of magnitude while the temperature was altered in the range from 6,000 to 14,000K. The Stark broadening parameters of transitions were derived from their simultaneous observation with the hydrogen Balmer alpha line. In addition, assuming a linear increase of Stark widths and shifts with electron density for non-hydrogenic lines, our measurements indicate a change of the Stark broadening-dependence of Hα over the considered electron density range. The presented results obtained for hydrated calcium sulfate (CaSO4⋅2H2O) can be extended to any kind of hydrogen containing compounds.

Comparative analysis of the role of atom and ion spectral lines in radiative heating of four types of space capsules

This paper presents the results of two-dimensional calculation of radiative heating of the Fire-II, Stardust, Orion, and PPTS (Prospected Piloted Transport System, Russia) spacecraft entering the dense atmosphere of the Earth with orbital and superorbital velocities. A specificity of the simulation is the allowance for atom and ion spectral lines with use of the NERAT-ASTEROID computer platform. This computer platform is destined for solving the complete system of equations of radiative gas dynamics of viscous, heatconducting, and physically and chemically nonequilibrium gas and radiative transfer in two- and threedimensional geometries. The spectral and optical properties of high-temperature gases are calculated in the entire flow field by ab-initio quasi-classical and quantum mechanical methods. The selective heat radiation transfer was calculated by the line-by-line method on specially generated computational grids over the radiation wavelength, which make possible appreciable saving of computer resources while providing detailed description of the contours of atomic lines.

Temperature diagnostic for laser-induced plasma by electron collision model

In this paper, using the collisions between ion and free electron, we analyze the conditions of electron collision equilibrium (ECE) for laser-induced plasma (LIP). Considering the collision excitation and de-excitation, we discuss the principle for temperature diagnostic for the three level ions for LIP. Taking the Ne v ion spectral lines in infrared as an example, for the intensity ratio of the (3-2) transition to the (2-1) transition, we compare the temperature in local thermal equilibrium and electron collision equilibrium when the intensity ratio varies from 0 to 1.8, and we obtain some important conclusions. This discussion is useful in the LIP diagnostic under the conditions of electron collision equilibrium.

Electron Impact Excitation and Ionization of Sulfur, Selenium, and Tellurium Vapors

Excitation and ionization processes of sulfur, selenium, and tellurium vapors by a low-energy (1–50 eV) electron impact have been investigated. The emission spectra are studied in the wavelength range 200–590 nm. The optical excitation functions for the most intense atomic and ionic spectral lines, as well as for molecular bands and emissions, are measured. The energy dependences of the total cross sections for the formation of positive and negative sulfur and selenium ions by the electron impact are also measured. The ionization energies of sulfur and selenium are determined, and the origin of the features observed in the measured curves is identified. It is found that, in the interval of temperatures, at which the experiments were carried out, the vapors of the researched objects, besides polyatomic molecules, also contain diatomic molecules of the studied elements at high concentrations. It is demonstrated that the atoms in excited states are mainly produced due to the dissociation of diatomic molecules.

Spectroscopic measurements of plasma temperatures and electron number density in a uranium hollow cathode discharge lamp

The plasma parameters including neutral species temperature, atomic excitation temperature and electron number density in a see-through type, homemade uranium hollow cathode discharge lamp with neon as a buffer gas have been investigated using optical emission spectroscopic techniques. The neutral species temperature has been measured using the Doppler broadening of a neon atomic spectral line. The atomic excitation temperature has been measured using the Boltzmann plot method utilizing uranium atomic spectral lines. The electron number density has been determined from the Saha-Boltzmann equation utilizing uranium atomic and ionic spectral lines. To the best of our knowledge, all these three plasma parameters are simultaneously measured for the first time in a uranium hollow cathode discharge lamp.

Factors affecting the formation of the radiation pre-peak at the operation of a Grimm-type source in pulsed DC mode.

The plasma emission pre-peaks of many atomic and ionic spectral lines of Cu and Ar were systematically investigated in a Grimm-type pulsed glow discharge (PGD). To register the pre-peaks with sufficient time resolution, a monochromator with photomultiplier detection was used. When the applied power exceeded a specific threshold, pre-peaks were found in all spectral lines investigated, and it was revealed that the electrical pre-peak was the cause of the atomic emission pre-peak. The form and intensity of the pre-peak radiation were, however, found to be different for different atomic emission lines. The excitation energy of the upper energy level of the atomic line transition, and factors related to recombination and self-absorption, were found to affect the emission pre-peak. Pre-peaks observed when using pulsed DC and pulsed radio-frequency power were compared. This investigation provides insight into best practice when selecting spectral lines most suitable for analytical spectrometry using PGD.

Correlation between Fe–V–C alloys surface hardness and plasma temperature via LIBS technique

Surface hardness is a very important characteristic of metals. Its monitoring plays a key role in industry. In the present paper, using laser induced breakdown spectroscopy (LIBS), Fe–V18%–C1% alloys with different heat treatments have been used for making the correlation between surface hardness and laser-induced plasma temperatures. All investigated samples were characterized by the same ferrite phase with different Vickers surface hardnesses. The differences in hardness values were attributed to the crystallite size changes. A linear relationship has been obtained between the Vickers surface hardness and the laser induced plasma temperature. For comparison the relation between surface hardness and the ratio of the vanadium ionic to atomic spectral lines intensities (VII/VI) provided good linear results too. However, adopting the proposed approach of using the plasma temperature, instead, is more reliable in view of the difficulties that could be encountered in choosing the proper ionic and atomic spectral lines. To validate this approach we have investigated the shock wave speed induced by laser interaction with the used samples. It was found that harder is the material faster is the shock wave. The determination of the surface hardness via measuring Te shows the feasibility of using LIBS as an easy and reliable method for in situ industrial application for production control.

Efficient algorithms for Stark–Zeeman spectral line shape calculations

A stochastic microfield formulation to treat particle motion effects in Stark-broadening of ion spectral lines by plasmas is extended to include an external uniform static magnetic field. The results are in good agreement with available line profile calculations from computer simulations. In addition, recently developed efficient algorithms are applied to Stark–Zeeman profile calculations with both static and dynamic ions.

Spectroscopic imaging of self-organization in high power impulse magnetron sputtering plasmas

Excitation and ionization conditions in traveling ionization zones of high power impulse magnetron sputtering plasmas were investigated using fast camera imaging through interference filters. The images, taken in end-on and side-on views using light of selected gas and target atom and ion spectral lines, suggest that ionization zones are regions of enhanced densities of electrons, and excited atoms and ions. Excited atoms and ions of the target material (Al) are strongly concentrated near the target surface. Images from the highest excitation energies exhibit the most localized regions, suggesting localized Ohmic heating consistent with double layer formation.

Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry

The effects and benefits of N2 addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N2 flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N2 did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N2 (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270nm/Mg(I)-285.213nm was utilized as a diagnostic tool for plasma robustness. The addition of N2 (20mLmin−1) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N2 than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N2-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N2 to the Ar-ICP.

Determination of Si/Al molar ratios in microporous zeolites using calibration-free laser induced breakdown spectroscopy

In this paper, the potential application of a calibration-free laser-induced breakdown spectroscopy (CF-LIBS) method for the determination of the silicon-to-aluminum molar ratio in microporous zeolites (with both intermediate and high silica contents) is discussed. Three different zeolite types, i.e., mordenite and zeolites type Y and ZSM-5, were analyzed in this study and were shown to have Si/Al molar ratios in the range between 2.3 and 51.8. Many ionic and neutral atomic spectral lines of silicon and aluminum were detected in the measured LIBS spectra in the spectral range 200–1000nm, but not all of the observed spectral lines are convenient for a CF-LIBS analysis. To increase the accuracy of the results, only lines with no or low self-absorption probability were selected. A systematic method is proposed to select spectral lines based on three main parameters: the transition probability (Einstein coefficient), the lower level energy of the observed transition and the number density ratio between singly ionized and neutral species (as calculated for Si and Al for the measured electron density and electron temperature). The calculated Si/Al molar ratios were close to that determined by wet chemical analysis with an average relative standard deviation of approximately 5% (maximum less than 15%). Our results point to the possibility of using CF-LIBS for analysis of these types of materials and for determination of Si/Al molar ratios.

Emissive characteristics of laser-produced tin plasma

Time-averaged radiation spectra of laser-produced erosion tin plasma are obtained. The peculiarities of formation of excited states of tin atoms and ions in a laser torch at the 1 and 7 mm away from a target have been investigated. The radiation dynamics of the most intense spectral lines of atoms and ions has been analyzed. The correlation of radiation intensities in the maximum for atom and ion spectral lines, recombination times of single- and double-charged ions in a laser-produced tin plasma, and the velocity of plasma propagation have been estimated.

Excitation Processes in Introduction of Bias Current to a Radio-frequency Glow Discharge Plasma Evaluated from Boltzmann Plots of Iron Atomic and Ionic Spectral Lines

A DC current, which was driven by the self-bias voltage, could be conducted in a radio-frequency-powered glow discharge plasma by connecting a low-pass filter circuit and a load resistor with the discharge tube. This current enhanced the intensity of emission spectra from the plasma largely. The intensities of iron atomic lines increased 35 - 50 times, whereas the sputtering rate was not changed by the current introduction. Boltzmann plots for iron atomic (Fe I) and ionic lines (Fe II) were investigated when the bias current was conducted, so that the excitation process relating to the intensity increase could be clarified. While the excitation temperature of the Fe I lines was slightly changed (3000 - 3600 K), that of the Fe II lines was drastically reduced from 7600 to 4300 K, which was close to the temperature of the Fe I lines at higher bias currents. Therefore, the plasma was changed towards an LTE condition so that both the Fe I and the Fe II lines could be excited through a common major process. The bias-current enhanced the density of electrons enabling low-lying excited energy levels (3 - 5 eV) of iron atom/ion to be much more populated, and they became the major colliding partners for the excitation of these iron species.

Spectral redistribution of gyroresonant photons in magnetized atmospheres of isolated compact stars

Aims. We analyze the spectral redistribution of gyroresonant photons in the course of radiation transfer through magnetized plasma atmospheres of isolated compact stars.

Study of laser-induced removal of co-deposits from tokamak plasma-facing components using ion diagnostics and optical spectroscopy

The paper presents studies of the application of ion diagnostics and optical spectroscopy for on-line measurement of the amount and characteristics of co-deposits from the laser-ablated surface of the plasma-facing components (e.g. graphite tiles). For removal of the co-deposit layer a repetitive Nd:YAG laser was used. Determination of the characteristics of ions emitted from the laser-illuminated targets was performed using ion collectors (on the basis of a time-of-flight method) and an optical spectrometer. The main ion stream parameters and spectral lines of deuterium and carbon or tungsten ions were measured depending on laser pulse parameters. The research proved that optical spectroscopy could be a convenient method for on-line observation of the co-deposited layer removal by means of laser ablation. In combination with the investigation of collected co-deposit dust, the performed study made it possible to state that laser-induced breakdown spectroscopy can be useful as a diagnostic method for the ablative co-deposited layer removal and the wall conditioning. The properties of modified surfaces of samples and collected dust (evaporated co-deposit) were determined using different measuring methods.

Principal component analysis of the main factors of line intensity enhancements observed in oscillating direct current plasma

Enhancement of emission line intensities by induced oscillations of direct current (DC) arc plasma with continuous aerosol sample supply was investigated using multivariate statistics. Principal component analysis (PCA) was employed to evaluate enhancements of 34 atomic spectral lines belonging to 33 elements and 35 ionic spectral lines belonging to 23 elements. Correlation and classification of the elements were done not only by a single property such as the first ionization energy, but also by considering other relevant parameters. Special attention was paid to the influence of the oxide bond strength in an attempt to clarify/predict the enhancement effect. Energies of vaporization, atomization, and excitation were also considered in the analysis. In the case of atomic lines, the best correlation between the enhancements and first ionization energies was obtained as a negative correlation, with weak consistency in grouping of elements in score plots. Conversely, in the case of ionic lines, the best correlation of the enhancements with the sum of the first ionization energies and oxide bond energies was obtained as a positive correlation, with four distinctive groups of elements. The role of the gas-phase atom-oxide bond energy in the entire enhancement effect is underlined.

Suprathermal plasma flows in current sheets formed in two- and three-dimensional magnetic configurations

Dynamics of the thermal and directed motions of argon plasma ions in current sheets formed in various magnetic configurations was investigated experimentally Measurements in three-dimensional magnetic configurations with an X line were carried out for the first time. The results of these measurements were compared with the data obtained in experiments with two-dimensional magnetic configurations. The ion temperature and the energies and velocities of directed plasma flows within the current sheet were determined by analyzing the shapes of argon ion spectral lines broadened due to the Doppler effect. It is found that, under the given experimental conditions, the axial magnetic field does not affect the ion temperature and plasma acceleration in the sheet.

Plasma dynamics during relativistic S-band magnetron operation

Results of a time- and space-resolved spectroscopic research studies of an S-band relativistic magnetron generating 1.5×108 W microwave power at f=2950 MHz, powered by a linear induction accelerator (450 kV, 4 kA, 150 ns), are presented. The cathode plasma electron density and temperature were obtained by analyzing Hα and Hβ hydrogen Ballmer series and carbon C II and C III ion spectral lines and the results of collision radiative modeling. It was shown that the microwave generation is accompanied by a significant increase in plasma density and ion temperature, up to ∼5×1016 cm−3 and ∼8 eV, respectively. The plasma electron temperature was found to be ∼8 eV. It was shown that the plasma expansion velocity in the axial direction reaches ∼107 cm/s and does not exceed ∼2×105 cm/s in the radial direction. In addition, it was shown that the plasma is not uniform and consists of separate plasma spots whose number increases during the accelerating pulse. Estimates of the plasma transport parameters and its interaction with microwave radiation are also discussed.

Spectral line selection for time-resolved investigations of laser-induced plasmas by an iterative Boltzmann plot method

The aim of this work is to provide a procedure to determine time-resolved electron temperatures with minimized relative errors by the Boltzmann plot method. The applied procedure consists of two parts, a systematic theoretical spectral line selection and an iterative Boltzmann plot algorithm. After a pre-selection of an appropriate non-disturbed or overlapped set of spectral lines of a particular atomic or ionic species Boltzmann plots are generated using experimentally recorded data for every time window and laser pulse energy of interest. Spectral lines with the highest average deviations from the regression function are assumed as being not representative for the considered ensemble of spectral lines and are therefore discarded gradually until a threshold value for the coefficient of determination is exceeded. Laser-induced breakdown spectroscopy (LIBS) is applied for time-resolved and spatially integrated investigations of plasmas on 1.1750 C75 steel alloy samples with laser pulse energies ranging between 200 µJ and 2 mJ. For the specific chemical composition of these samples a selection of atomic and ionic Fe spectral lines has been carried out. In spite of the fact that only laser pulse energies in the low millijoule regime are applied the final sets of spectral lines comprise in total 61 Fe I and 12 Fe II emission lines. By applying this method electron temperatures can be determined with averaged relative errors of down to 1.8% for Fe I and 4.4% for Fe II emission lines.