Ionization Of Vapor Research Articles

Initiation of ecton processes by interaction of a plasma with a microprotrusion on a metal surface

Evolution of rapid (∼10 ns) Ohmic overheating of a microprotrusion on a surface in contact with a plasma by emission current is studied taking into account the energy carried by plasma ions and electrons, as well as Ohmic heating, emissive source of energy release (Nottingham effect), and heat removal due to heat conduction. Plasma parameters were considered in the range of n = 1014−1020 cm−3 and T e = 0.1 eV−10 keV. The threshold value of energy transferred to the surface from the plasma is found to be 200 MW/cm2; above this value, heating becomes explosive (namely, an increase in the temperature growth rate (δ2 T/δt 2 > 0) and in passing current (δJ/δt > 0) is observed in the final stage at T ∼ 104 K and j ∼ 108 A/cm2). In spite of the fact that Ohmic heating does not play any significant role for plasmas with a density lower than 10 18 cm−3 because the current is limited by the space charge of electrons, rapid overheating of top of microprotrusion is observed much sooner (over a time period of ∼1 ns) when the threshold is exceeded. In this case, intense ionization of vapor of the wall material leads to an increase in the plasma density at the surface, and the heating becomes of the Ohmic explosion type. Such conditions for the formation of a micrĭxplosion on the surface and of an ecton accompanying it can be created during the interaction of a plasma with the cathode, anode, or an insulated wall and may lead to the formation of cathode and anode spots, as well as unipolar arcs.

Secondary Electrospray Ionization (SESI) of Ambient Vapors for Explosive Detection at Concentrations Below Parts Per Trillion

We determine the sensitivity of several commercial atmospheric pressure ionization mass spectrometers towards ambient vapors, ionized by contact with an electrospray of acidified or ammoniated solvent, a technique often referred to as secondary electrospray ionization (SESI). Although a record limit of detection of 0.2 x 10(-12) atmospheres (0.2 ppt) is found for explosives such as PETN and 0.4 ppt for TNT (without preconcentration), this still implies the need for some 10(8)-10(9) vapor molecules/s for positive identification of explosives. This extremely inefficient use of sample is partly due to low charging probability ( approximately 10(-4)), finite ion transmission, and counting probability in the mass spectrometer (1/10 in quadrupoles), and a variable combination of duty cycle and background noise responsible typically for a 10(3) factor loss of useful signal.

Semiempirical equation of state with few constants for cesium vapor

Statistical analysis is performed of consistency of the known experimental data on the density of cesium vapor. A semiempirical equation of state with few constants is employed, which is based on “pseudogroup” expansions of pressure and density in powers of activity. The second group integral is theoretically calculated using spectroscopic and quantum-mechanical data on atomic interaction. A modification of this equation of state is suggested, which enables one to approximate experimental data both at low and moderate densities and in the near-critical region. Equations of state are derived, which describe both the data of single experiments and the majority of these data taken together. The experimental data indicative of the significant effect of anomalous ionization of cesium vapor on its thermodynamic behavior are shown to be invalid.

Use of Langmuir probe for analysis of charged particles in metal vapour generated by electron beam heating

During electron beam evaporation of metal, a certain fraction of the vapor is ionized due to various processes such as Saha ionization and electron impact. These charge particles constitute a plasma which expands along with the vapour. To know about parameters of this plasma viz. electron temperature, electron density, plasma potential, we have used a disc type Langmuir probe inside the plasma. The measured electron temperature was found to be about ∼0.15eV (1740K) and measured plasma potential was ∼1V. The low value of electron temperature as compared to the source temperature, established that plasma cools significantly while traversing the distance between the source and the point of measurement. Again as the electron temperature was approximately same as the ion temperature of the vapor (expected to be same as kinetic temperature of vapor for collisional flow), we concluded that a kind of equilibrium had been established in the plasma. Finally, various processes responsible for ionization of the vapor are discussed and it was found that both Saha ionization and electron impact processes play important role in ionization of the uranium vapor generated by electron beam heating.

Water molecule ionization by charged particles: a short review

We present both singly differential and total cross sections for the direct ionization of water vapour by electrons as well as by ions (protons and alpha particles). An ab-initio calculation has been made by using the first Born approximation and an accurate molecular wave function proposed by Moccia [J. Chem. Phys. 40, 2186 (1964)]. The results of this model are compared to experimental data and to results obtained via semi-empirical models.

Discharge phenomena associated with a preheated wire explosion in vacuum: Theory and comparison with experiment

This paper presents the experimental and simulation results of electrical explosions of preheated tungsten wires at a current rise time of several tens of nanoseconds and at a current density of ∼108A∕cm2. The electrical characteristics of wire explosion (WE) were measured. The image of a wire during the electrical explosion was obtained with the help of a framing camera. The proposed magnetohydrodynamic (MHD) model takes into account different stages of WE, namely, the wire heating and vaporization, the phase transition, and the shunting discharge. Two different mathematical approaches were used for WE simulation at different stages. At the first stage, the simulation included a code describing the wire state. At the second stage, the shunting discharge was simulated together with the wire state. The simulation code includes the set of MHD equations, the equilibrium equation of state (density and temperature-dependent pressure and specific internal energy), electron transport models (density and temperature-dependent electrical conductivity and thermal conductivity), and electric circuit equations. Thermionic emission and vapor ionization initiate the plasma layer, which develops around the wire core and supports the shunting discharge. The calculated waveforms of the wire voltage and current, as well as the velocity of the expanding plasma, are in a good agreement with the experimental data.

Transient Cathode Spot Operation at a Microprotrusion in a Vacuum Arc

A physical model and system of equations was formulated to describe transient cathode spot evolution at a single protrusion. The model considered the self-consistent processes including protrusion heating, kinetics of cathode vaporization, plasma generation, and current continuity. The time dependencies of spot current, current density, and protrusion size were calculated, taking into account the heat flux from the plasma (surface heat source) and Joule energy (volume source). The plasma density, temperature, degree of vapor ionization, electron current fraction, and cathode erosion rate were calculated as functions of the protrusion size, which reduced in time during the spot operation. It was shown that the spot operation on the protrusion was limited by the disappearance of the protrusion due to cathode erosion. The protrusion disappearance time determined the duration of the transient arc spot at a single protrusion. It was calculated that 1-5 mum protrusions reduce their size significantly due to evaporation in 0.5-10 mus, respectively. The smaller time of protrusion destruction occurs due to it relatively high heating, which was mostly by the heat flux from the surrounding plasma.

Spectroscopic studies of laser induced aluminum plasma using fundamental, second and third harmonics of a Nd:YAG laser

In the present work, we have studied the spatial evolution of the aluminum plasma produced by the fundamental (1064 nm), second (532 nm) and third (355 nm) harmonics of a Q-switched pulsed Nd:YAG laser. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using Boltzmann plot method whereas the electron number density has been determined from the Stark broadened profiles. Besides we have studied the variation of excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure. In addition, we have performed quantitative analysis of photon absorption and vapor ionization mechanism at three laser wavelengths and estimated the inverse bremsstrahlung (IB) absorption and photoionization (PI) coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the experimental results.

Inelastic-collision cross sections for the interactions of totally stripped H, He and C ions with liquid water

The HKS and CDW-EIS models are implemented to determine single ionization cross sections (SICS) corresponding to the impact of H +, He 2+ and C 6+ ions on liquid water, for incident energies from 0.3 to 10 MeV/u. Corrected expressions for the HKS method have been used. The same kind of initial electron wave functions and binding energies have been used with both methods, in order to compare the formalisms themselves. Double and single differential as well as total SICS of liquid water have been calculated by use of both formalisms and comparisons have been made between their theoretical predictions. Also, these results have been compared with experimental values reported previously for ionization of water vapor due to protons and alpha particles. Despite its sophistication, the CDW-EIS method does not show better results than the more simple HKS model when comparing liquid water single and double differential cross sections with experimental water vapor values. However, once the excitation cross sections are included to determine electronic stopping cross sections in liquid water, the results based on the CDW-EIS method provide the best agreement when compared with corresponding data published in ICRU reports, obtaining discrepancies of about 9%, 16% and 19% for incident protons, alpha particles and carbon ions respectively.

Ab initiocalculation of differential and total cross sections for the ionization of water vapor by protons

We present both differential and total cross sections for the direct ionization of water vapor by protons in the incident energy range $0.1--100\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. Different theoretical models are investigated within the framework of the Born approximation in order to evaluate the influence of each pairwise Coulomb interaction term among the ejected electron, the scattered proton, and the residual ionized target in the final state. In all these models, the ground state of the water molecule is described by means of an accurate molecular wave function proposed by Moccia [J. Chem. Phys. 40, 2186 (1964)]. The results of these full ab initio quantum-mechanical treatments are compared to experimental data. Good agreement is generally observed, showing that sophisticated Born models are sufficient to explain all the experimental data, including doubly differential, singly differential, and total cross sections.

The HKS model for electron production in liquid water by light ions

The HKS model developed to determine ionization cross sections (ICS) for the interaction of non-relativistic ions with matter, is used for 0.5MeV protons impinging on liquid water and some inconsistencies between the single (SDCS) and double (DDCS) differential cross section values predicted by the formalism are found. To overcome this problem, new SDCS and DDCS formulas are determined analytically by use of the transition probabilities published by Hansen and Kocbach [J.P. Hansen, L. Kocbach, J. Phys. B 22 (1989) L71]. The new cross section expressions applied to the 0.5MeV proton on liquid water case, give perfectly consistent SDCS and DDCS values. Furthermore, SDCS and DDCS values predicted from the new formulas for ionization of liquid water by protons (0.5–4.2MeV/u) and alpha particles (0.3–0.5MeV/u) are compared with corresponding experimental cross section values reported in the literature for water vapor ionization. Despite of the simplicity of the HKS model, accurate secondary electron energy distributions can be obtained, even for electron energies as low as 10eV. Although the same accuracy cannot be achieved for electron angular distributions, the HKS formalism can still be used when these distributions are not critical.

Influence of pulse duration on the plasma characteristics in high-power pulsed magnetron discharges

High-power pulsed magnetron discharges have drawn an increasing interest as an approach to produce highly ionized metallic vapor. In this paper we propose to study how the plasma composition and the deposition rate are influenced by the pulse duration. The plasma is studied by time-resolved optical emission and absorption spectroscopies and the deposition rate is controlled thanks to a quartz microbalance. The pulse length is varied between 2.5 and 20μs at 2 and 10mTorr in pure argon. The sputtered material is titanium. For a constant discharge power, the deposition rate increases as the pulse length decreases. With 5μs pulse, for an average power of 300W, the deposition rate is ∼70% of the deposition rate obtained in direct current magnetron sputtering at the same power. The increase of deposition rate can be related to the sputtering regime. For long pulses, self-sputtering seems to occur as demonstrated by time-resolved optical emission diagnostic of the discharge. In contrary, the metallic vapor ionization rate, as determined by absorption measurements, diminishes as the pulses are shortened. Nevertheless, the ionization rate is in the range of 50% for 5μs pulses while it lies below 10% in the case of a classical continuous magnetron discharge.

Optical breakdown in aluminum vapor induced by ultraviolet laser radiation

Theoretical analysis of the evolution of nonequilibrium plasma induced by ultraviolet laser radiation is carried out. Intensity threshold values are studied by mathematical modeling as a function of laser-pulse wavelength. Basic mechanisms of nonequilibrium ionization of aluminum vapor are analyzed and the dominant role of photo-processes, namely, resonant and nonresonant photoexcitation and photoionization, is shown. The modeling results are in good agreement with experimental data on optical breakdown in aluminum vapor by the excimer laser radiation in nanosecond and microsecond range.

Transient Enhanced Diffusion of B in Si Implanted with Decaborane Cluster Ions

Cluster ions, obtained by ionization of decaborane vapor are considered for implantation of B into Si to form very shallow junctions required for the next generations of metal oxide semiconductor devices. While shallow B implantation can thus be achieved with relatively large implantation energies, the final junction depth is also defined by diffusion during annealing, particularly by transient enhanced diffusion (TED). TED of B in Si implanted with mass analyzed cluster ions at energies of 2, 5, and 12 keV is compared with TED from 1.2 keV ions. No difference was found between TED of B implanted in Si with the cluster and the monomer ions of the equivalent energy and dose. © 2002 The Electrochemical Society. All rights reserved.

Total, Partial, and Electron-Capture Cross Sections for Ionization of Water Vapor by 20–150 keV Protons

We present experimental results for proton ionization of water molecules based on a novel event by event analysis of the different ions produced (and lost). We are able to obtain mass analyzed product ion signals (e.g., H2O+, OH+, O+, O++, H+) in coincidence with the projectile analyzed after the collision, i.e., either being H+, neutral H after single electron capture during the ionization event, or H- after double electron capture. After proper calibration we are thus able to determine a complete set of cross sections for the ionization of a molecular target by protons including the total and the partial cross sections and in addition also the direct ionization and the electron capture cross sections.

Experimental study of lithium target under high power load

This paper presents experimental research on simulation of a free liquid lithium surface under high heat flux impact for divertor application. Capillary porous structure (CPS) was taken to form the free liquid metal surface imitating divertor target plate. Experiments were performed in the SPRUT-4 linear plasma device with electron beam as power source. Lithium-filled targets were investigated at 1–50 MW/ m 2 heat loads in steady state. Lithium evaporation, energy and mass balance, surface temperature, vapor ionization, lithium plasma parameters and radiation were studied. Detailed thermal analysis was made to study heat flows in the target and their correspondence with experimental observations. Durable operation of the setup was possible in the range 1–20 MW/ m 2 without damage of the structure. The relevance of the experimental performance to divertor condition is analyzed.

Adhesion of copper on polyimide deposited by arc-enhanced deposition

Polyimide films of Kapton EN were coated with copper by arc-enhanced deposition. This deposition method offers the possibility to influence the degree of ionization by setting the anodic arc current without varying other deposition parameters. Estimation of the electron density depending on the anodic arc current is given by flat probe measurements. Adhesion measurements by pull test and peel test were carried out to examine the influence of vapor ionization on adhesion. The adhesion measurements do not show a uniform dependence on the anodic arc current and bias voltage, and the adhesion strength never reached values obtained by thermally evaporated copper coatings. Apparently, either ion impact or vacuum ultraviolet radiation of the anodic arc damages the polymer by a significant amount.

Stepwise ionization of hydroquinone vapor by monochromatic radiation

Processes of stepwise ionization of hydroquinone vapor by radiation in the range 315–275 nm were studied using photoionization spectroscopy techniques. The two-step ionization process yielding molecular ions was found to prevail at a laser power density up to ∼107 W/cm2. As the radiation intensity increases, the progressively stronger and deeper degradation takes place via dissociation of the molecular and, probably, fragment ions due to absorption of at least one additional photon. The slow process of the formation of C5H6O0 ions at an effective rate constant of the order of 106 s−1 was observed.

Effect of Vortex Motion of Stabilizing Liquid Wall on Properties of Arc in Water Plasma Torcha

ABSTRACT: In water stabilized plasma torches an electric arc is ignited in a centre of water vortex which is created in cylindrical arc chamber with tangential water injection. The arc is stabilized by an interaction with inner wall of the vortex. Principle physical mechanisms which control arc properties and parameters of generated plasma jet are evaporation of water wall and heating and ionization of vapour flowing from the wall into the arc column. The vortex movement of water is necessary to maintain fixed shape of inner wall of the vortex due to inertial forces. Published model of mechanisms of water stabilized arc does not consider effect of movement of water on mechanisms of arc 1. The aim of investigation described in this paper is theoretical and experimental study of the effect of movement of water and induced tangential component of velocity of plasma in the arc column on properties of arc and generated plasma jet.

Production of ions and microdroplets in conducting-liquid emitters

The characteristics of the finely dispersed component of an electrodynamic source of indium and tin ions were studied. Microdroplets are emitted above a threshold value of the beam current, and oscillations of the ion current with a frequency of order 10 MHz are excited at the same time. At the maximum values of the ion current the microdroplet sizes range from 20 to 400 A. The mechanisms for producing light ions and charged microdroplets in sources of this type were analyzed. These are field ionization of vapor and thermal dispersion of liquid, respectively.