Ionic composition of a humid air plasma under ionizing radiation

A kinetic model is proposed for ion–molecular processes involving charged particles of a humid air plasma produced by a fast electron beam. The model includes more than 600 processes involving electrons and 41 positive and 14 negative ions, including hydrated ions H₃O⁺ (H₂O) _n and O ₂ ^? (H₂O) _n with n = 1, 2, …, 12. The energy costs of production of electron–ion pairs and electronic and vibrational (for water molecules, also rotational) excitation of molecules are calculated in nitrogen, oxygen, water vapor, air, and humid air. A method is proposed for calculating the energy costs in mixtures by the calculation data in pure gases. The evolution of the plasma composition is studied by the numerical solution of a system of 56 time-dependent balance equations for the number of charged particles of plasma by the fourth-order Runge–Kutta method. The steady-state composition of plasma is determined by solving nonlinear steady-state balance equations for the ionization rates of humid air from 10 to 10¹⁶ cm^–3/s and the fraction of water molecules from 10^–3% to 1.5%. It is established that, for water vapor content (the ratio of the number density of water molecules to the total number density of air molecules) of 0.015–1.5% in air at atmospheric pressure and room temperature, the main ion species are two types of positive ions H₃O⁺ (H₂O) _n with the number of water molecules n = 5, 6 and three species of negative ions O ₂ ^? (H₂O) _n with n = 5, 8, 9.     

Spectroscopic diagnostics of a laser erosion plasma formed from CuSbS<Subscript>2</Subscript> polycrystals

The spectra and dynamics of emission from regions of a laser plasma torch located at different distances from a polycrystalline CuSbS₂ target irradiated by a neodymium laser (W=(3–5)×10⁸ W/cm², ?=20 ns, f=12 Hz, 73x03BB;=1.06μm) were investigated. The emission data were used to estimate the average temperature (≤0.82 eV) and the electron density ((1.82?1.92)×10¹⁶ cm^?3) in the laser torch and the recombination times of ions (t _r(S²⁺)=15 ns, t _r(Cu⁺)=65?85 ns), as well as to analyze the efficiency of filling of excited atomic levels. A model describing the target destruction and the evolution of the processes accompanying spread of the laser plasma is proposed.     

X-ray spectroscopy diagnostics of a recombining plasma in laboratory astrophysics studies

The investigation of a recombining laser plasma is topical primarily because it can be used to simulate the interaction between plasma jets in astrophysical objects. It has been shown that the relative intensities of transitions of a resonance series of He-like multicharged ions can be used for the diagnostics of the recombining plasma. It has been found that the intensities of the indicated transitions for ions with the nuclear charge number Z _n ~ 10 are sensitive to the plasma density in the range N _e ~ 10¹⁶–10²⁰ cm^–3 at temperatures of 10–100 eV. The calculations performed for the F VIII ion have determined the parameters of plasma jets created at the ELFIE nanosecond laser facility (Ecole Polytechnique, France) in order to simulate astrophysical phenomena. The resulting universal calculation dependences can be used to diagnose different recombining plasmas containing helium-like fluorine ions.     

Mechanisms of ionization of <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript>-centers in laser media on the basis of LiF crystals

F₂ color centers with a superhigh concentration (5000-cm^–1 absorption coefficient at 450 nm) were formed by high-density electron beams in a layer of LiF crystals of micrometer thickness. The F₂-centers excited by high-power nanosecond wide-band optical pulses (the “soft” pumping regime) efficiently amplified the laser radiation and showed high stability under these conditions. A low stability of F₂-centers to laser radiation (the “hard” excitation regime) is explained by the dissociation of (F ₂ ⁺ , F^–) pairs induced by two-step ionization of F₂-centers: (2hν > 4.5 eV) → F₂ → (F₂)* → F ₂ ⁺ + e; F + e → F^–; F ₂ ⁺ + F^– → 3F.     

Plasma-volume generation of H<Superscript>−</Superscript> ions in a low-voltage xenon-hydrogen discharge. II

A low-voltage xenon-hydrogen discharge is considered theoretically at an interelectrode distance of L = 1 cm and cathode emission current densities of j _s = 2–20 A/cm². Basic parameters of the discharge plasma, in particular, the total hydrogen and xenon densities, are optimized to attain the maximum possible density of negative hydrogen ions \(N_{H^ - } (L)\) at the plasma-anode boundary. The distributions of the plasma parameters over the discharge gap are calculated for optimized regimes. According to calculations, at intermediate cathode emission current densities (j _s ≈ 5–10 A/cm²) in optimized discharge regimes, the density of negative hydrogen ions in the anode region of the plasma is \(N_{H^ - } (L)\) ≈ (1.5–2.5) × 10¹² cm^?3 and the total plasma pressure is p ₀ = 0.5–0.6 Torr.     

Magnetized Quark-Gluon Plasma at the LHC

In QCD, the strengths of the large scale temperature dependent chromomagnetic, B₃, B₈, and usual magnetic, H fields spontaneously generated in quark-gluon plasma after the deconfinement phase transition (DPT), are estimated. The consistent at high temperature effective potential accounting for the oneloop plus daisy diagrams is used. The heavy ion collisions at the LHC and temperatures T not much higher than the phase transition temperature T_d are considered. The critical temperature for the magnetized plasma is found to be T_d (H) ～ 110–120 MeV. This is essentially lower compared to the zero field value T_d (H=0) ～ 160–180 MeV usually discussed in the literature. Due to contribution of quarks, the color magnetic fields act as the sources generating H. The strengths of the fields are B₃(T), B₈(T) ～ 10¹⁸–10¹⁹ G, H(T) ～ 10¹⁶–10¹⁷ G for temperatures T ～ 160–220 MeV. At temperatures T < 110–120 MeV the effective potential minimum value being negative approaches to zero. This is signaling the absence of the background fields and color confinement.     

Losses through bremsstrahlung in relativistic and ultra-relativistic region of electron temperatures of plasma

The losses through bremsstrahlung in a sufficiently diluted hydrogen plasma (plasma with infinitely large Debye-Hückel radius) are calculated for the relativistic (kT?mc ²) and ultra-relativistic (kT?mc ²) region of electron temperatures. (m is the rest mass of the electron). In the ultra-relativistic temperature region the amount of energyI ^tot emitted by 1 cm³ of plasma per sec as a result of electron-ion and electron-electron collisions is given by

$$I^{tot} = 3 \cdot 39 \times 10^{ - 29} \frac{{n^2 }}{\mu }[1 \cdot 86 + E_1 (\mu )]Wattcm^{ - 3} $$     

On the possibility of laser generation without inversion on the fine-structure levels of a helium atom

It is shown that laser generation is possible in principle upon coherent excitation according to the V-scheme of the (1s2p)³ P _j levels with j = 1, 2 of a helium atom from the (1s2s)³ S ₁ level of the same atom when the latter level is, in turn, populated by electron or proton impact.     

Determination of the absolute concentration of B,Al, Ga,and Si atoms in a nonequilibrium plasma by the reabsorption-distorted intensity ratios in resonance multiplets

The recently developed method of spectroscopic determination of the concentration of boron atoms in a nonequilibrium plasma is extended to B, Al, Ga, and Si atoms and generalized by taking into account the gas temperature and the non-Boltzmann distribution of the sublevel populations of the ground state multiplet structure of the atoms. The approach suggested is based on the measurement of the reabsorption-distorted intensity ratios of pairs of spectral lines having the same upper level and belonging to the resonance multiplet. It is shown that, at a sufficiently large optical thickness of the plasma along the line of observation, the measured values of the intensity ratios depend on the plasma gas temperature T and the product NL of the total concentration N of normal atoms and the length L of the plasma column along the line of observation. Hence, to determine the concentration N using the resonance doublets of B, Al, and Ga atoms, it is necessary to have data about the temperature T. The structure of the resonance multiplet of Si allows measurement of three independent intensity ratios. This circumstance not only makes possible the simultaneous and purely spectroscopic determination of N and T but also enables one to perform internal testing of the applicability of the suggested method under real experimental conditions. The intensity ratios are calculated for the resonance multiplets of B, Al, Ga, and Si in the regions T = 300–6500 K and NL = 10⁷–10¹⁵ cm^?3 m. The calculation results and the range of applicability of the method are discussed.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.     

Weak antilocalization in a three-dimensional topological insulator based on a high-mobility HgTe film

The up-conversion luminescence of Er³⁺ from the ²H_11/2, ⁴S_3/2, and ⁴F_9/2 levels in nanocrystals of Y_0.95(1?x)Yb_0.95xEr_0.05PO₄ (x = 0, 0.3, 0.5, 0.7, 1) orthophosphates activated with Er³⁺ ions has been studied under the excitation of Yb³⁺ ions to the ²F_5/2 level by 972-nm cw laser radiation. Broadband radiation in the wavelength range of 370–900 nm has been observed at certain power densities of exciting laser radiation; this broadband radiation is absent in the case of excitation of the powders under study by pulsed laser radiation with a wavelength of 972 nm at a pulse repetition frequency of 10 Hz and a duration of a pulse of 15 ns. Experimental data indicating that this radiation is thermal in nature have been presented.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Anlagerungskoeffizienten und Driftgeschwindigkeiten von Elektronen in Luft

Electron drift velocities and attachment coefficients were measured in dry air (E/p=0.1–30 V/cm Torr) and in a 9∶1 nitrogen/oxygen mixture (E/p=0.2–3 V/cm Torr) in the pressure range from 50 to 200 Torr, using a modified spark chamber technique. The primary electrons were released by anα-particle. The temporal development of the electron density in the gap was determined from the amplitude of the current due to the avalanches, which were produced by applying high voltage pulses at different delay times. — It was found that in air the dissociative attachment sets in at higherE/p (～10–15 V/cm Torr) than in oxygen. At lowerE/p three body attachment is predominant. — When the high voltage pulses were applied after the transit time of the primary electrons, electron avalanches still appeared. It was concluded that they were started by electrons which were detached from negative ions. The estimated detachment rates indicate the formation of O ₂ ^? ions at lowE/p and of O^? ions at higherE/p.     

Interplay of Curie-type and Pauli-type magnetic susceptibilities in HCl-doped polyaniline pellets

The static magnetic susceptibility (χ) of own-made HCl-doped polyaniline pellets is investigated experimentally over the full range of the protonation level Y and in the temperature (T) range 10–300 K.The obtained results suggest that χ and the electrical conductivity σ – which is known from previous work – are interrelated.Namely, there is a weakly Y dependent crossover temperature T ^* where both χ and σ undergo notable changes.In χ, this refers to a simultaneous enhancement (reduction) of the Pauli-type susceptibility χ _P and reduction (enhancement) of the Curie constant C at T = T ^* when T increases (decreases).Below T < T ^*, where thermal effects are weak to moderate, a steep increase of χ _P(Y) around Y = 0.3 occurs together with a drop of C(Y).The above findings are consistent with a picture in which, at T ^*, spins that disappear from C reappear in χ _P, and vice versa.This model is used to address the longitudinal and transversal electron localisation lengths as functions of Y, the former being estimated to take values in the range 7–8 Åand the latter in the range 1–2 Å.     

Special features of the <Emphasis Type="Italic">K</Emphasis> = 0 channel in nuclear fission

The opinion that the K = 0 fission channel is completely closed if the spin J and the parity π of the nucleus undergoing fission do not satisfy the condition (?1) ^J = π is widespread. On the basis of a detailed analysis of quantum numbers characterizing the rotational states of deformed nuclei, it is shown that this opinion is erroneous. In fact, the K = 0 channel may be partly open. Its suppression is caused by special features of fission barriers in the state being considered. It is also shown that factors that suppress the K = 0channel may exist even in states characterized by J and π values such that they satisfy the condition (?1) ^J = π. More precise information about the contribution of the K = 0 channel may be obtained by measuring the hexadecapole component of the angular distribution of fragments originating from the slow-neutron-induced fission of aligned nuclei.     

Distribution function and electron state density in nonequilibrium plasma created by dye laser

Ultracold nonequilibrium plasma created by a dye laser has been studied by the molecular dynamics method. Electrons and protons in this model of nonequilibrium plasma interacted according to the Coulomb law. In the case of electron-proton interaction and a distance between particles r < a ₀ (Bohr radius), the interaction energy is constant, e ²/a ₀ (e is the charge of electron). An initial proton kinetic energy is set randomly so that the average kinetic energy is 0.01–1 K. Initial full electron energy is also set randomly, but at the same time it is positive; i.e., all the electrons according to our task are located in the continuous spectrum. Average kinetic electron energy per one particle varies from 1 to 50 K. The motion equations in periodical boundary condition for this system have been solved by molecular dynamics method. We have calculated the distribution function in the region near the ionization threshold. The distribution function is being described using electron state density in the nearest neighbor approximation with activity correction.     

Equilibrium and stability of the charged particles’ fluxes drifting crosswise to the strong magnetic field at the expense of the Hall charge separation

The current equilibrium is investigated, where the generation of the Hall electric field on the magnetic Debye radius r _B = B ₀/(4πen _e) is considered by the drifting of the relativistic electrons crosswise to the strong magnetic field. In this case, the electron propagation is possible at the distance d that is essentially larger than the electron radius of the backward reflection in the magnetic field r ₀ ? m _e v _z c/(eB ₀). The instability of the joint drift motion of ions and electrons is investigated for the frequency oscillation w much higher than the ion cyclotron frequency w _Bi and by 4π n _i m _i c ² ? B ₀ ² and (k · B ₀) = 0. It is shown that the resonance effects by the ion beam’s plasma frequency w ? kv ₀ = w _pi leads to the generation of the nonpotential perturbations with the characteristic increment Imw ～ 10^?1 ÷ 10^{? 2} w _pi. Estimates show that the instability, associated with the propagation of the high-energy ion beam through the strong magnetic field, can essentially be like the edge-localized mode in tokamaks.     

Investigation of the D(<Superscript>3</Superscript>He, <Emphasis Type="Italic">p</Emphasis>)<Superscript>4</Superscript>He Reaction in the Astrophysical Energy Region of 18–30 keV

The D(³He, p)⁴He reaction is first investigated in a solid target of deuterated zirconium (ZrD) in the ³He⁺ ion energy range E_He = 18–30 (E = 7.2?12.0keV keV in the center-of-mass system) with a step of 2 keV. The electron screening potential U_e = (617.8 ± 154.7) eV and the D(³He, p)⁴He reaction enhancement factors are experimentally determined in the given energy range. The measured electron screening potential is six times higher than in gaseous targets. This can be due to the ZrD lattice effects, which have not been studied either theoretically or experimentally so far. The D(³He, p)⁴He reaction has been investigated at the pulsed plasma Hall accelerator (Tomsk).     

Proton-proton interaction with high multiplicity at energy of 70 GeV (proposal)

The goal of the proposed experiment is to investigate the collective behavior of particles in the process of multiple hadron production in pp interaction pp → n _π π + 2N at the beam energy E_lab = 70 GeV. The domain of high multiplicity n _π = 30–40, or z = n/\(\bar n\) = 4–6, will be studied. Near the threshold of reaction n _π → 69, z → z_th = 8.2, all particles acquire small relative momentum Δq < 1/R, where R is the dimension of the particle production region. As a consequence of multiboson interference, a number of collective effects may show up: (a) a drastic increase in the partial cross section σ(n) of production of n identical particles is expected, compared with commonly accepted extrapolation; (b) the formation of jets consisting of identical particles may occur as a result of the multiboson Bose-Einstein correlation (BEC) effect; (c) a large fluctuation of charged n(π⁺,π^?) and neutral n(π⁰) components and onset of centauros or chiral condensate effects are anticipated; (d) an increase in the rate of direct γ as a result of the bremsstrahlung in the partonic cascade and annihilation of π⁺π^? → nγ in dense and cold pionic gas or condensate is expected. In the domain of high multiplicity z ≥ 5, a major part of the c.m. energy \(\sqrt s = 11.6\) GeV is materialized, leading to a high-density thermalized hadronic system. Under this condition, a phase transition to cold quark-gluon plasma (QGP) may occur. The search for QGP signatures like large intermittency in the phase-space particle distribution and an enhanced rate of direct photons will be performed. The experimental setup is designed for detection of rare high-multiplicity events. The experiment is to be carried out at the extracted proton beam of the IHEP U-70 accelerator. The required beam intensity is ～10⁷ s^?1. Under the assumption that the partial cross section σ(n _π = 35) = 10-1 nb, the anticipated counting rate is 10-1 events/h. The multiboson BEC enhancement may drastically increase the counting rate.     

X-ray photoelectron spectroscopy of FeP phosphide

The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe³⁺ (d ⁵) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J _H ) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP₆)^15– clusters in the IS state.