Electron Concentration In Plasma Research Articles

Hydrogen Reduction of MoF6 and Molybdenum Carbide Formation in RF Inductively Coupled Low-Pressure Discharge: Experiment and Equilibrium Thermodynamics Consideration

The physical plasma parameters, temperature and electron number density, are studied in the RF-IC (RF inductively coupled) discharge at a reduced pressure of 3 Torr in mixtures of MoF6 with Ar, H2 and CH4. The emission spectra of mixtures are investigated. It is shown that in the presence of argon, the concentration of free electrons in plasma and dissociation rate of MoF6 increase. A main role of molecular hydrogen is the generation of atomic hydrogen that binds atomic fluorine and leads to the formation of gaseous and solid products. Exhaust gas mixtures exiting the reactor are analyzed by mass spectrometry. It is shown that for all cases, the conversion of MoF6 into reaction products is close to 100%. A thermodynamic analysis of the equilibrium composition of MoF6 systems with Ar, H2 and CH4 was carried out and the obtained results are in good agreement with experimentally observed composition of the solid and gas phases. Analysis of solid deposits from mixture MoF6/H2/Ar revealed the presence of molybdenum powder and large amount of amorphous MoFx. The deposit obtained from mixtures with methane, MoF6/H2/Ar/CH4, contained crystalline molybdenum carbide, Mo3C2.

Effect of pulse duration on the energy delivery under nonlinear propagation of tightly focused Cr:forsterite laser radiation in bulk silicon

We have investigated nonlinear laser ̶ matter interaction inside silicon under tight focusing conditions by continuously tuning driving pulse duration from femtosecond to picosecond timescales. Such tailoring of laser pulse width provides a new route for energy delivery into a microvolume avoiding two-photon absorption and plasma defocusing in the pre-focal region. As a result, we have achieved values of saturated deposited energy density and plasma electron concentration of as high as 1 kJ cm−3 and 1019 cm−3 respectively, which is lower than the threshold of irreversible structural transformation. For further increase of energy delivery inside silicon, a two-color technique supported by extremely tight focusing can be realized, forming a roadmap to the 3D industrial micromachining of planar bulk silicon.

Acceleration of electrons in the interaction of a subterawatt laser pulse with a nonuniform plasma

We consider the effect of nonlinear self-focusing and self-modulation processes on the acceleration of electrons in the interaction of a subterawatt femtosecond laser pulse with a gas jet plasma. A three-dimensional particle-in-cell (3D PIC) simulation of the interaction of laser radiation with a low-density nonuniform plasma shows that laser pulse self-focusing that arises when the critical power of relativistic self-focusing determined by the local concentration of plasma electrons exceeds the pulse power results in efficient generation of a plasma wave. Due to a decrease in the phase velocity of the wake plasma wave generated via self-modulation of the laser pulse, electrons are trapped into the accelerating phase of the plasma wave and are accelerated to energies of ∼10 MeV. It is demonstrated that under the conditions for limiting the electrons’ acceleration region by the length of their dephasing, quasi-monoenergetic electron bunches with a characteristic energy of ∼9 MeV can be produced. The effective temperature of the accelerated electrons and their angular distribution, obtained by 3D PIC simulation, are in good agreement with those determined in the experiment.

Experimental Study of Inhomogeneous Reflex-Discharge Plasma Using Microwave Refraction Interferometry

The phase shift at the plasma interferometry with oblique microwaves and microwaves passing through the center of a plasma formation has been calculated. The critical density Ncr and the critical radius rcr of a plasma layer, at which microwaves do not hit the horn antenna, are calculated for various radial plasma distribution functions. The time dependences of the phase shift for the transverse and oblique probing modes are experimentally measured. Using the phase shifts determined by the both methods, the time dependence of the product NpL of the electron concentration in plasma and the optical path length of a microwave beam in vacuum is found, and the average plasma density is estimated.

Increase in the output power and efficiency of a He-Ne laser under combined excitation with pumping by a transverse high-frequency field

The influence of a high-frequency field in the range of 900–2400 MHz on the lasing power and efficiency of laser radiation with a wavelength of 0.63 μm, applied to the capillary tube of a He-Ne laser with direct-current electrical discharge has been studied. The existence of an optimum field frequency, at which the increase in lasing power requires the minimum power of an external high-frequency generator, is established. The optimum field frequency is determined to be close to the electron plasma frequency corresponding to the optimal concentration of plasma electrons in the regime of excitation by a direct-curret discharge.

Estimation of electron concentration in plasma and plasma frequency in the vicinity of a hypersonic aircraft that moves in atmosphere and analysis of propagation frequencies of electromagnetic waves in such plasma

Electron concentration in plasma and plasma frequency are estimated for the plasma that is formed in the vicinity of a hypersonic aircraft that moves in atmosphere. The frequencies of electromagnetic waves that may propagate in plasma emerging in the vicinity of the aircraft are determined. Formulas that make it possible to analytically (rather than graphically) calculate electron concentration in plasma at altitudes of 30, 60, and 90 km are derived for two speeds. Several specific features of variations in the electron concentration in plasma depending on the above altitudes and speeds are presented. Quasi-periodic variations in the plasma concentration can be obtained using an increase and decrease in the speed of aircraft.

Radiation reflection by a plasma with electron temperature anisotropy

The reflection of a test electromagnetic wave normally impinging on a plasma surface is investigated within the formalism of the surface impedance. The plasma is assumed to possess an anisotropic two-temperature bi-Maxwellian electron velocity distribution function. The linearly polarized impinging wave during reflection transforms into an elliptically polarized one, the degree of ellipticity depending on the electron temperature anisotropy. Polarization modifications of the reflected wave are particularly important in the conditions of the anomalous skin-effect, when the influence of the wave magnetic field on the electron kinetics in the skin layer is strong. Relations are reported connecting the reflected wave basic parameters to those of the reflecting plasma surface, making possible, through the experimental determination of the reflected wave characteristics, to find the plasma electron concentration and the two effective temperatures.

Influence of electron concentration and temperature on fullerene formation in a carbon plasma

The influence of electron concentration in ionized carbon vapor on C 60 fullerene formation was theoretically investigated. By considering C 60 molecule assembly at one or two intermediate stages of cluster collision we determined the plasma parameters (temperature and electron concentration) optimal for the fullerene synthesis. The estimations made showed that waves of electron concentration in plasma changed the rate of C 60 fullerene assembling.

Large-scale stratification of the ionosphere during earthquake preparation

Modulation of ionospheric plasma density by acoustic waves (AW) is investigated. A rigorous electrodynamic model of the interaction of acoustic waves, generated by the lithospheric displacements during the seismic event preparation, with the cold dense ionospheric plasma in the presence of a magnetic field is constructed in conjunction with the actual height variations of the plasma particles' mobility and conductivity tensors in the ionosphere. A mechanism of creation of ionospheric inhomogeneities with different scales and with various degree of disturbance ΔN/N0=10−4–10−5 (N0 is the concentration of plasma electrons (ions) in background ionospheric plasma) is presented.

Numerical simulation of the mutual conversion of ordinary and extraordinary waves in a magnetised plasma by artificial ionospheric turbulence

Abstract Some effects of normal mode coupling in weakly anisotropic inhomogeneous plasma are analysed on the basis of the numerical solution of transfer equations for the Stokes parameters. The numerical analysis of normal mode conversion on a set of isolated irregularities demonstrates the possibility of an effective polarisation transformation on such structures. It is shown that by the appropriate selection of discrete irregularities of the external magnetic field direction or plasma electron concentration resulting in radio-wave refraction, one can control electromagnetic radiation polarisation characteristics. Analytical expressions for mean Stokes parameters have been obtained for the rare isolated irregularities. The opportunity for the simulation of mutual wave conversion processes in the ionospheric heating experiments is discussed.

Measurement of electron concentration in plasma of an impulse erosion accelerator. (USSR): V Ya Gubarev et al,Zh Tekh Fiz, 42 (4), April 1972, 826–829 ( in Russian)

Measurement of electron concentration in plasma of an impulse erosion accelerator. (USSR): V Ya Gubarev et al,Zh Tekh Fiz, 42 (4), April 1972, 826–829 ( in Russian)

Measurement of the electron concentration in a plasma generated by a high-velocity electron beam

The probing of gas and plasma flows by beams of accelerated electrons is now coming into wide use [1,2]. In colliding with particles of the gas being investigated the beam electrons ionize these particles and either generate an independent plasma or increase the ion concentration in the plasma under investigation. This can introduce consideable error into the measurements of plasma parameters. Consequently, the problem can arise of the need to evaluate such error. This can be done by our investigating parameters of the plasma generated by ionization of the gas by a beam of accelerated electrons. The ionization of a gas by an electron beam produces a plasma whose parameters, such as electron concentration N, the effective frequency of electron collisions, etc . , can be easily varied by a suitable selection of gas, or by our varying the gas pressure, the electronbeam current and energy, etc. Modification or displacement of the zone occupied by the plasma can be important in certain applications. Such modification can evidently be most readily achieved with a plasma generated by an electron beam. Available experimental data [8, 4] pertain to ionization of a rarefied gas by means of pulsed beams (pulses on the order of a few psec at pressures ranging from 10 -s to 10 "~ mm Hg. At low pressures and short pulses the ionization processes play a fundamental role in plasma generation, since in this case there is little elee~on recombination and diffusion. ConsequenrIy, data obtained under these conditions are not applicable to the case of gas ionization by a steady electron beam. Preliminary results from measurement of electron concentration in plasma generated in air, helium, and argon by a high-velocity electron beam at current intensities varying between 0.1 and 0.6 mA are presented in this paper. The mean concentration of electrons in the plasma was measured along the beam cross section, with the plasma-column diameter assumed equal to the bright region of the gas ionized by the beam (Fig. 1). This model is somewhat crude approximation of phenomena actually taking place in fire beam, since it does not take account of irregularity in electron distribution across the beam, and of electron diffusion outside the bright zone. However, consideration of these phenomena is extremely complex. The electron concentration in the plasma was measured by means of a superhigh frequency resonator in the three-centimeter range of wave-lengths [6]o A cylindrical resonator with TMox 0 oscillations and an electron beam aIong its axis was selected for these experiments. The resonator was 26.4 mm in diameter and 10 mm in height. The electron concentration in the pIasma was determined in the usual manner from change in the transmission ratio and from the shift in the resonance frequency of the resonator during passage of an electron beam through it.. The experimental setup is shown diagrammatically on Fig. 2. The energy from superhigh frequency oscillations at 8680 mHz was fed from a klystron generator to the resonator located in a vacuum chamber together with the waveguides. The controlled admission of gas to the chamber made possible variation of the ionized gas pressure within the required limits,

Analysis of cold cathode glow neon discharges without anode glow or positive column †

Abstract Plasma data given previously for the negative glow and Faraday dark space of near-normal cold cathode discharges in neon are supplemented by results, described briefly, for similar discharges without positive column or anode glow. The axial plasma electron concentration curves, which are sharply peaked near the cathode dark space when the cathode rays are strongly attenuated towards the anode, flatten markedly as the attenuation decreases.

Dependence of laser radiant power on electron concentration in a He-Ne plasma

1. In a tube of diameter 4 mm with a He—Ne mixture, a decrease was observed in the vhf resonator shift (decrease in the plasma electron concentration) with increase of discharge current, beginning at a certain current value. Possible causes are: a) an increase of electron temperature with increase in discharge current because of rarefaction of the gas in the small diameter tube; b) the appearance of groups of fast electrons with increase of current; c) the appearance of current instabilities, confirmed by the generation of low-frequency noise. 2. The appearance of induced emission at λ=3.39 μ is accompanied by a noticeable increase in the vhf resonator frequency shift (by an increase in plasma electron concentration). The cause may be photoionization of excited neon atoms, including cascade ionization. 3. The dependence of the radiant power at λ = 0.6328 μ on the discharge current (in the absence of lasing at λ = 3.39 μ) follows that of ne(Id). Therefore, the decrease of radiant power with increase of discharge current, beginning at a definite value of ne, cannot be explained by increase of the population of the lower operating 2p4 neon level. Evidently, this decrease is due to a decrease in the population of the upper operating 3s2 neon level because of the fall in ne, or the electron temperature plays a more substantial part here than does variation of ne.

The negative glow and Faraday dark space in near-normal neon discharges†

Radial and axial electrostatic probe measurements have been made of the negative glow and Faraday dark space of some weakly ‘ anomalous ’ cold cathode discharges in neon at pressures near 1 torr. These have been analysed and discussed with the aim of extending previous diffusion theories. Either an anode glow or positive column was present. The axial plasma electron concentration had a maximum in the negative glow, with much smaller values in the Faraday dark space. Some features of the axial pattern were consistent with an increase in diffusion coefficient on moving towards the anode. This could be due to increase in mean electron energy or to the onset of ‘ subnormal ’ conditions with expansion of the wall-sheath, the latter showing by development of bell-shaped radial concentration curves ; but there is doubt as to the applicability of ordinary probe theory under ‘ subnormal ’ conditions. The length of the Faraday dark space is consistent with the head of the positive column appearing when diffusion, m...

Plane Collisionless Sheaths between Field-Modified Emitting Electrodes and Thermally Ionized Plasmas Exemplified by Cesium

This paper describes a theory for plane collisionless sheaths separating plasmas ionized by thermal electrons from emitting electrodes affected by sheath fields. Examples for cesium plasmas and thermionic-diode configurations show sheath effects over ranges of conditions: temperatures from 1400° to 2400°K for electrodes, from 1600° to 2400°K for plasma atoms and ions, and from 1700° to 2700°K for plasma electrons; plasma-electron number densities from 1012 to 1015 cm−3; and work functions from 1.5 to 5 V. Sheath drops from 0 to 2.1.V and net currents from 0 to over 100 A cm−2 result. Over-all sheath characteristics correlate with work function minus plasma potential, plasma-electron concentration (Nep), electrode temperature (TE), and an emission Debye length λDE≈6.9(TE/Nep)1/2. Effective sheath widths range from 1.7 to 2.6 emission Debye lengths.

Discussion of paper by F. L. Scarf, ‘Effect of coherent density fluctuations on the radar determination of total electron content’

Howard et al. [1965] and Yoh et al. [1966] have recently reported on a beautiful set of radar experiments in which group and phase delay introduced by the cislunar medium were interpreted in terms of a mean plasma electron concentration. Electron concentrations found by these techniques appear to be very much higher than those derived by other means, such as from whistlers [Carpenter, 1966], from micropulsations [Watanabe, 1965], or on theoretical grounds [Dessler and Michel, 1966]. Scarf [1966] subsequently attempted to explain the discrepancy as an effect of coherent density fluctuation on the mean propagation constants of the plasma, In what follows we show that the effect discussed by Scarf is probably unimportant and hence that some other explanation of the curious discrepancy between the results of the radar propagation experiments and the currently accepted model of the magnetospheric tail must be sought.

204. Determination of reflex klystron plasma electron concentration: V P Chirkov,Izmerit Tekh, No 6, June 1966, 41–42 (in Russian)

204. Determination of reflex klystron plasma electron concentration: V P Chirkov,Izmerit Tekh, No 6, June 1966, 41–42 (in Russian)

Evaluation of electron concentration in plasma of a reflex klystron

The basic function of the above method consists in evaluating electron concentration of plasma with a precision adequate for the requirements of plasma diagnostics. This method serves to study internal processes which occur in klystron plasma and to simulate the effect on the klystron output parameters of various electromagnetic factors which deform the flows. This method can also be used in klystron vacuum technology for determining the degree of purity of a vacuum bulb.

Radial and Axial Electron Concentrations in an Oscillating Low Voltage Arc†

ABSTRACT Measurements have been made of the plasma electron concentration (n) along and perpendicular to the axis of a low pressure, low voltage oscillating discharge with cylindrical symmetry, maintained by an axially directed beam from a small cathode. The contours of n are sharply peaked radially at the axis between the cathode and oscillation front (meniscus), but are much flatter beyond the meniscus, near the anode. The radial contours between cathode and meniscus conform approximately to those predicted theoretically for axial electron generation, and those near the anode to those predicted theoretically for ion generation proportional to electron concentration. Contours near the meniscus, when not completely unobtainable on account of the oscillations, exhibit apparent radial maxima and minima associated with the beam diverging from the meniscus.