Effects of Energetic Electrons on Collector and Source Potentials in a Finite Ion Temperature Plasma

Formation of the potential in a two-electron-temperature plasma region facing a floating collector was studied theoretically with a kinetic plasma-sheath model and by electrostatic particle simulation. The electrons were described by truncated full Maxwellian velocity distribution functions and the ions by an accelerated half-Maxwellian velocity distribution function. The collector potential and the plasma source sheath or presheath potential drop were evaluated as functions of the hot to cool electron temperature ratio and the hot electron density ratio using Vlasov and Poison equations. The results showed that the presheath potential drop varied continuously with electron composition ratio for lower values of the electron temperature ratio, while for higher values in a narrow composition ratio range, triple values of the potential were found. Of the two physically acceptable values, the lower was characterized by the cool electrons and the higher by the hot electrons. It is anticipated that a current-free double layer structure is formed in the plasma system between these two potential regions. The collector floating potential, as a function of electron composition ratio, is mainly dominated by the hot electrons, since already a small value of hot electron current is sufficient to compensate the ion saturation current. In order to complete the theoretical investigation we also study the hydrogen plasma system with the XPDP1 particule-in-cell simulation code composed at Berkeley. At certain plasma parameter values formation of a double layer structure was observed. The potential Values on the upper and lower side of the double layer, as well as that of the collector floating potential, corresponded very well to the calculated values. On the upper side the plasma was composed of ions, accelerated through the source sheath potential drop, and electrons consisting of cool full Maxwellian and hot truncated full Maxwellian populations. On the lower side only hot electrons and ions additionally accelerated through the double layer were found.     

Calculation of Recombination and Ionization Coefficients in Argon

Various methods for calculating electron-ion recombination and ionization coefficients for argon (α and S) have been developed in the past. For given values of electron temperature and electron density, a large dispersion exists between the different results due to a great number of parameters. We have developed the method based on the collisional-radiative model to calculate α and S for limited conditions (atmospheric pressure; strong resonance radiation absorption) in order to obtain realistic values applicable in real cases such as arc plasmas. Influences of resonance radiation absorption and atom-atom collisions have been studied. The collisional-radiative recombination coefficient has been compared with results obtained by other calculation methods: the best agreement occurs with the “bottleneck” model for high values of electron density and temperature. Finally the comparison with available experimental results shows a good agreement between our computed values and experimental values when experimental and theoretical conditions are analogous.     

Estimation of the SEM beam diameter by video-signal curves from a trapezoidal structure: 1. Simulation experiment

An experiment is performed to determine the electron beam diameter using a comparison of a video signal curve from a relief structure and the one calculated based on a simplified model of curve formation. Rather than the use of an experimental curve for comparison, this model experiment suggests the use of a curve calculated from the data on electron scattering in substrate by the Monte Carlo method. The comparison results revealed the difference between the calculated diameter value and the value of diameter of a model incident beam. It appeared that the parameters of the relief structure and the electron beam affected the calculated diameter values; as a result, these values can vary by several hundred percent in some cases.     

Time Relativity in the Dynamics of Open Quantum Systems

Various methods for determining the Coulomb logarithm in the kinetic theory of transport and various variants of the choice of the plasma screening constant, taking into account and disregarding the contribution of the ion component and the boundary value of the electron wavevector are considered. The correlation of ions is taken into account using the Ornstein–Zernike integral equation in the hypernetted-chain approximation. It is found that the effect of ion correlation in a nondegenerate plasma is weak, while in a degenerate plasma, this effect must be taken into account when screening is determined by the electron component alone. The calculated values of the electrical conductivity of a hydrogen plasma are compared with the values determined experimentally in the megabar pressure range. It is shown that the values of the Coulomb logarithm can indeed be smaller than unity. Special experiments are proposed for a more exact determination of the Coulomb logarithm in a magnetic field for extremely high pressures, for which electron scattering by ions prevails.     

Inequalities of the electron density at the nucleus and radial expectation values of the ground state for the lithium isoelectronic sequence

The electron density at the nucleus, ρ(0), and the radial expectation values, (-2≤n≤10), of the ground state for the lithium isoelectronic sequence are calculated with a full core plus correlation (FCPC) wavefunctions. By using these obtained expectation values, the accurate inequalities of the electron density at the nucleus and the radial expectation values derived by Gálvez and Porras for these systems are examined and verified. The final results show that FCPC wavefunctions used in this work can give satisfactory results in full configuration space.     

Mikrowellenabsorption in der Nähe der 2. Harmonischen der Elektronenzyklotronfrequenz

In plasmas produced by microwave power the electron density displays a dependence on the magnetic field strength obviously asymmetric with respect to the harmonics of the electron cyclotron frequency. In regions of the magnetic field strength just above the harmonics there are extremely high values of electron density, the density values dropping sharply off towards the other wing of the harmonics. Absorption experiments near the second harmonic at low microwave power — the plasma being produced by different means — reveal a resonant absorption structure in the magnetic field region above the harmonic. This can be attributed to excitation of geometrical eigenmodes of electrostatic. waves propagating perpendicular to the magnetic field (Bernstein waves).     

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by Etimes B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.     

Determination of plasma properties with electron drainage to the probe

Certain aspects of probe diagnostics of plasmas which are related to the electron drainage to the probe are discussed. Even small values of the drainage parameter greatly distort the second derivative of the electron current drawn by the probe. At large values of the drainage parameter, the zero of the second derivative occurs well away from the actual space potential. Also at large values of the drainage parameter, the distribution function which is being sought is proportional to the first derivative of the electron current drawn by the probe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 34–39, March, 1984.     

X-ray radiation and runaway electron beam spectra at a nanosecond discharge in atmospheric-pressure air

The dependences of the electron beam intensity and X-ray dose on the thickness of metal foils (Al, Cu) in a nanosecond discharge initiated in atmospheric-pressure air are studied theoretically and experimentally. Calculated curves of electron beam attenuation in aluminum and X-ray dose attenuation in copper agree well with experimental data. It is found that the amplitude of a super-short avalanche electron beam and the X-ray exposure dose reach maximal values at different values of the interelectrode gap. When the length of the cathode??s edge with a small radius of curvature increases, an interelectrode gap maximizing the amplitude of the runaway electron current shrinks.     

Estimates of energies of core exchange

Energies of core exchange, δ, for some first row elements have been estimated from thermodynamic data and experimental core electron binding energies. Values of energies of core exchange extend the equivalent cores method to allow the calculation of absolute binding energies as well as shifts. In some cases it is possible to estimate the differences in binding energy without requiring heats of formation of gaseous cations. The values of δ obtained from LCAO-MO-SCF calculations show similar trends although the absolute values may differ by a few electron volts.     

The Rates of Formation of Negative Ions for Some Halocarbons in Nitrogen and in Argon-Nitrogen Mixtures in Dependence on the Mean Electron Energy

An experimental electron swarm method with a special electron capture detector arrangement (ECD) is described which allows one to modify the energy of low energetic electrons from thermal to 2.8 eV by means of radio-frequency voltage. Using theoretically calculated values of electron energy distribution functions in nitrogen and argon the attachment coefficients and the formation rates of negative ions for chlorobenzene, benzyl chloride, chloroform, methylene chloride, nitrobenzene, propyl iodide, trichloroethylene and carbon disulfide were determined in dependence on the mean electron energy. Mean electron attachment cross sections could be estimated.     

Langmuir Probe Diagnostics of a Low Temperature Non-Isothermal Plasma in a Weak Magnetic Field

This article presents measurements by a cylindrical Langmuir probe in the plasma of a DC cylindrical magnetron discharge át the pressure 1.5 Pa that aim at the experimental assessment of the influence of a weak magnetic field to the estimation of the electron density when using conventional methods of probe data interpretation. The probe data was obtained under the presence of a weak magnetic field in the range 1.10^?2?5.10^?2 T. The influence of the magnetic field on the electron probe current is experimentally assessed for two cylindrical probes with different radii, 50 μm and 21 μm. This assessment is based on comparison of the values of the electron density estimated from the electron current part with the values of the positive ion density estimated from the positive ion current part of the probe characteristic respectively by assuming that at the magnetic field strengths used in the present study the probe positive ion currents are possible to be assumed as uninfluenced by the magnetic field. For interpretation of the probe positive ion current two theories are used and compared to each other: the radial motion model by Allen, Boyd and Reynolds [10] and Chen [11] and the model that accounts for the collisions of positive ions with neutrals in the probe space charge sheath that we call Chen-Talbot model [8]. At lower magnetic field 3 · 10^?2 T the positive ion density values interpreted by using the Chen-Talbot model [8] are in better agreement with the values of electron density compared to those obtained by using the theory [10,11]; therefore the model [8] is used for calculation of the positive ion density from the probe data at higher magnetic fields. The comparison of the positive ion and electron density values calculated from the same probe data at higher magnetic fields shows that up to the magnetic field strength 4 . 10^?2 T with the probe 100 μm and up to 5 . 10^?2 T with the probe 42 μm in diameter respectively the decrease of the magnitude of the electron current at the space potential due to the magnetic field does not exceed the error limits that are usual for Langmuir probe measurements (absolute error ±20%).     

Kα X-ray satellite spectra of Ti, V, Cr and Mn induced by photons

K X-ray emission spectra of Ti, V, Cr and Mn generated by photon excitation have been studied with a crystal spectrometer. The measured energy shifts of K_α satellite relative to the diagram line are compared with values obtained by electron excitation and with different theoretical estimates. The present experimental values of K_αL¹/K_αL⁰ relative intensities are compared with values obtained by electron excitation.      

Determination of the electron temperature of the tenuous pulsed argon ion laser plasma by means of the line intensity ratio technique

The validity of the diagnostic line-intensity ratio method for determination of the electron temperature was examined for a tenuous, NLTE pulsed argon ion laser plasma. Recently measured cross sections for simultaneous excitation and ionization of the upper levels of the argon ion laser were used and averaged over the velocity distribution, assumed Maxwellian. The electron temperature was determined by observing the sidelight intensity ratio of doublet 4765 Å and quartet 4806 Å transitions, and it was found to be 1.65 eV. This result is in agreement with electron temperature values obtained by the time resolved measurement and the double probe method, respectively. The theory of the positive column, where wall effects are not considered, gives somewhat larger values as an upper bound.     

Size determination of Acipenser ruthenus spermatozoa in different types of electron microscopy

In this study three types of scanning electron microscopes were used for the size determination of spermatozoa of sterlet Acipenser ruthenus – high vacuum scanning electron microscope (SEM, JEOL 6300), environmental scanning electron microscope (ESEM, Quanta 200 FEG), field emission scanning electron microscope (FESEM, JEOL 7401F) with cryoattachment Alto 2500 (Gatan) and transmission electron microscope (TEM, JEOL 1010). The use of particular microscopes was tied with different specimen preparation techniques. The aim of this study was to evaluate to what degree the type of used electron microscope can influence the size of different parts of spermatozoa. For high vacuum SEM the specimen was prepared using two slightly different procedures. After chemical fixation with 2.5% glutaraldehyde in 0.1 M phosphate buffer and post-fixation by 1% osmium tetroxide, the specimen was dehydrated by acetone series and dried either by critical point method or by means of t-butylalcohol. For ESEM fresh, unfixed material was used, which was dropped on microscopic copper grids. In FESEM working in cryo-mode the specimen was observed in a frozen state. Ultrathin sections from chemically fixed and Epon embedded specimens were prepared for TEM observation. Distinct parts of sterlet spermatozoa were measured in each microscope and the data obtained was statistically processed. Results confirmed that the classical chemical procedure of specimen preparation for SEM including critical point drying method led to a significant contraction of all measured values, which could deviate up to 30% in comparison with values measured on the fresh chemically untreated specimen in ESEM. Surprisingly sperm dimensions determinated on ultrathin sections by TEM are comparable with values obtained in ESEM or FESEM.     

Electret mechanism of electron beam capture by the magnetic field of a betatron

The mechanism of electron capture into acceleration that takes into account the electret properties of the accelerating chamber shell is described. The electron capture into acceleration is a self-consistent problem. It is demonstrated that the electron capture into acceleration is caused by the interaction of the injected electrons with the electric field of the charge created on the side interior wall of the chamber by electrons dropped out of the acceleration. The spectrum of the captured electrons is not normal. A large number of low-energy electrons are presented in the spectrum. Two and more peaks previously unknown are revealed in the dependence of the captured charge on the injected charge for large values of the injected charge. The results obtained are in agreement with the data of previous experimental studies. The captured charge and the dose rate of bremsstrahlung from a target correspond to their actual values for betatrons with accelerated electron energies of 6 and 10 MeV. Results of simulation can be used to design accelerating chambers and electron injection systems of betatrons and other cyclic accelerators. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 35–45, December, 2006.     

Inelastic quasiparticle lifetimes of the Shockley surface state band on Ni(111)

We present a study of the low-energy quasiparticle lifetimes of the Shockley surface state on the Ni(111) surface with scanning tunnelling spectroscopy. By measuring the coherence length of the decaying standing wave pattern at straight step edges electron and hole lifetimes have been determined. The values of the lifetime measured on this ferromagnetic surface show to be considerable smaller than the values obtained from noble metal surfaces. This is explained by differences in the electron density of states at the Fermi energy but has to include substantial spin-flip scattering. Furthermore hole lifetimes appear to be larger than electron lifetimes with the same excitation energy. Although only results for the majority spin component are presented, a spin-dependent selfenergy is expected.     

Angular distribution of electron temperature and density in a laser-ablation plume

The angular distribution of electron temperature and density in a laser-ablation plume has been studied for the first time. The electron temperature ranges from 0.1 to 0.5 eV and is only weakly dependent on the angle in the low-intensity range studied here. In contrast, the typical ion energy is about 2 orders of magnitude larger, and its angular distribution is more peaked about the target normal. The derived values of the electron density are in agreement with the measured values of ion density.     

Variable density formation by intense microwave beams near the critical density

Modification of electron density of an inhomogeneous, unmagnetized plasma by the relativistic ponderomotive force of intense microwave beams near the critical density is studied. Using the Maxwell and fluid equations and taking into account the relativistic mass, relativistic ponderomotive force, linear inhomogeneity for electron temperature, and tangential inhomogeneity for electron density, the non‐linear electron density, non‐linear dielectric permittivity, and non‐linear wave equations are derived. Results show that positive and negative values of σ₁ and σ₂ (degree of inhomogeneity of the background electron density and electron temperature, respectively) parameters can affect the electric and magnetic field profiles. In addition, profiles of the non‐linear electron density indicate that by decreasing the σ₁ parameter, the amplitude of the peaks increases near the critical density. For positive values of the σ₂ parameter, by increasing this parameter the amplitude of the peaks increases, while for negative values of the σ₂ parameter, by decreasing this parameter the amplitude of the peaks increases.     

Spectroscopic Mapping of the Nonequilibrium between Electron and Excitation Temperatures in a 1 ATM Helium ARC

The thermostatic states of a 100 amp, 1.016 bar, free-burning helium short arc with a 10 mm electrode gap are mapped from spectroscopic measurements at eight cross sections. The theoretical model used is a multifluids model extended to consider nonequilibrium between electron and excitation temperatures, as well as simple nonequilibrium among excited electronic levels. Seven helium lines are used to determine population densities and upper level excitation temperatures. The electron density is calculated from continuum intensity measurements at C4690. Electron temperatures are found from an astrophysical method suggested by Athay and Menzel. The effective total excitation temperature is obtained by iteration using the multifluids model. The results indicate total excitation temperature values close to the usually calculated "LTE" temperatures, but electron temperatures up to three times larger than the total excitation temperature on the arc centerline near the electrodes. The ratio is approximately 1.5 in the middle of the arc. The heavy particle kinetic temperatures appear to follow the electron temperature, except near the anode, where they drop to values smaller than the total excitation temperatures.