Determination of the electron temperature of a degenerate semiconductor in quantizing fields under heating by an electric field

Investigations of the Shubnikov-de Haas oscillation of the transverse magnetoresistance due to the magnitude of the electric field in n-type InSb with 5 · 10¹⁵, 3 · 10¹⁶ cm^–3 concentrations at a 4.2 °K temperature are carried out herein. A method is proposed to determine the electron temperature T_e; dependences of T_e on the electric and magnetic fields in the sample are obtained for a transversely oriented magnetic field. The relaxation time of the electron energy is estimated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 96–100, February, 1972.     

Special features of the operation of an electron-ionization CO2-laser at high pressures

A study was made of the excitation of the working medium of a CO₂-laser at a pressure of up to 8 atm by an electron beam of duration 15 · 10^–9 sec. Results are given of the energy dissipation in a CO₂:N₂-13 gas medium in the whole range of pressures with E₀/p = (18–38) V /cm · mm Hg. The dependences of the time of appearance of the stimulated radiation with respect to the current pulse are given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 40–44, April, 1976.     

Spatial distribution of albedo particles on altitudes ∼500 km

Spatial distributions of energetic charged particles, neutrons and gamma rays at altitude 500 km (below the radiation belts of the Earth), obtained by the measurements of two apparatuses on board the Intercosmos-17 satellite, are presented. The latitudinal dependences, [i.e. the variation of flux with vertical cut-off rigidity of the measurement point], for neutrons (E _n = 1 –30 MeV), gamma rays (E =0·15–6 MeV), secondary electrons (E _e > 100 MeV) and for primary protons coming from the west and the east, respectively, are given. The main characteristic, the ratioN _p/N _e of the counting rate of the particles in the polar regionN _p(R_vert< <0·1 GeV/c) and on the equatorN _e(R_vert > 16 GeV/c), is obtained for the various types of particles. This value is 10 for neutrons, 3.7 for gamma rays, 1·8 for electrons, 11 for protons in westward direction, 10 for protons in eastward direction. The latitude profile of neutrons and gamma rays is in a good agreement with calculations assuming their production by nuclear reactions of primary cosmic rays with nuclei of the atmosphere. The weakening of rigidity dependence of protons coming from east in comparison with those coming from the west, is interpreted as the cause of additional proton albedo flux. The equality of albedo electron fluxes (E_e = 100–3500 MeV) from these directions is observed. With the use of the shadowing effect the obtained data on electron-positron component are consistent with the flux of albedo positrons (E_e + > 3·5 GeV) of the value (0·5±0·2) m^–2. s^–1. ster^–1. The possibility of abundance of albedo positrons above electrons at these altitudes for the energy intervalE=0·2÷0·3 GeV is indicated.     

Effect of vibrational kinetics of He2 + ions on the afterglow of a discharge in helium

A decaying weakly ionized helium plasma [n_e=(0.2–1.1)·10¹¹ cm^–3, p=(40–70) mm Hg] was studied experimentally. It is shown that the experimental time dependences of the intensities of atomic lines and molecular bands in the afterglow phase can be explained if the vibrational kinetics of He₂ ⁺ ions is included in the analysis. Analysis of the measurements shows that for n_e 10¹¹ cm^–3 and N_a 10¹⁸ cm^–3 deexcitation of He₂ ⁺ ions occurs primarily as a result of inelastic collisions with helium atoms. Based on the experimental data, an approximate value was obtained for the rate constants of the vibrational relaxation of molecular helium ions 10^–16 cm³/sec. These results are used for making a qualitative analysis of the distribution of He₂ ⁺ ions over the vibrational states in the discharge phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–96, November, 1986.     

Determination of the Concentration of Electrons in the Laser Plasma of Helium

The dependence of the Stark width of the spectral line of He II P 468.6 nm on the electron concentration in the laser plasma of helium for the range of electron densities N _e = (1–10)·10²³ m^–3 and electron temperatures of the order of 60 kK has been measured. The results obtained correspond well to Griem's theoretical data. An empirical relation is suggested which makes it possible to reliably determine the electron concentration from measured halfwidths in the investigated range of N _e.     

Anomalous plasma phenomena of hollow cathode arc discharge

Magnetically confined argon plasma produced by hollow cathode arc discharge has been studied in different experimental conditions, with discharge current from 10–50 A, vessel argon pressure between 10^–3 and 10^–4 torr (1 torr=133·32 Pa) and axial magnetic field up to 0·12 T. The plasma density measured by a cylindrical Langmuir probe is found to be 10¹⁹ to 4 × 10¹⁹ m^–3 and the electron temperatureT _e varies between 2·5 and 4·8 eV. When an external axial magnetic field is applied the plasma temperature decreases with the increase in the magnetic field intensity until it reaches a minimum value at 0·075T and then increases with the same rate. This has been interpreted as high frequency waves excitation due to electron beam-plasma interaction, which explains the electron density jumps with the magnetic field intensity. Enhanced plasma transport across the magnetic field is studied and classified as anomalous diffusion.     

Energy scaling of quasi-monoenergetic electron beams from laser wakefields driven by 40-TW ultra-short pulses

By focusing 40-TW, 30-fs laser pulses to the peak intensity of 10¹⁹ W/cm² onto a supersonic He gas jet, we generate quasi-monoenergetic electron beams for plasma density in the specific range 1.5×10¹⁹ cm^-3≤n_e≤3.5×10¹⁹ cm^-3. We show that the energy, charge, divergence and pointing stability of the beam can be controlled by changing n_e, and that higher electron energies and more stable beams are produced for lower densities. The observed variations are explained physically by the interplay among pump depletion and dephasing between accelerated electrons and plasma wave. Two-dimensional particle-in-cell simulations support the explanation by showing the evolution of the laser pulse in plasma and the specifics of electron injection and acceleration. An optimized quasi-monoenergetic beam of over 300 MeV and 10 mrad angular divergence is demonstrated at a plasma density of n_e≃1.5×10¹⁹ cm^-3. PACS 52.35.-g; 52.38.Hb; 52.38.Kd; 52.65.-y     

Features of current carrier scattering in epitaxial films

The properties of epitaxial cadmium selenide films obtained by condensation in a vacuum on mica substrates under almost equilibrium conditions are investigated. The temperature dependences of the conductivity and current carrier mobility and concentration are studied. The electron concentration in the films depended on the gas phase composition (coevaporation of CdSe + Se or CdSe + In) and varied between 5·10¹⁰cm^–3 and 3.5·10¹⁸. It is shown that the current carrier scattering mechanism depends on their concentration and production conditions. For n₁ 10¹⁶ cm^–2 (T_S520C),n₂ < 10¹⁵ (T_S=630C), scattering on intercrystallite barriers predominated. For n₁ and n₂ greater than the quantities mentioned, scattering by ionized defects becomes dominant. It is established that the magnitude of the intercrystallite barrier in films with 10¹⁵ < n < 10¹⁶ cm^–3 is comparatively small and does not exceed 4·10^–3 eV, whereupon scattering at the barriers is not explicitly manifest. Concentrations of the ionized centers, magnitudes of the intercrystallite barriers, and ionization energies of the donor levels are determined for films obtained under different conditions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 98–103, September, 1977.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Intense low energy positron beams

Intense positron beams are under development or being considered at several laboratories. Already today a few accelerator based high intensity, low brightness e⁺ beams exist producing of the order of 10⁸–10⁹ e⁺/s. Several laboratories are aiming at high intensity, high brightness e⁺ beams with intensities greater than 10⁹ e⁺/s and current densities of the order of 10¹³–10¹⁴ e⁺ s^–1 cm^–2. Intense e⁺ beams can be realized in two ways (or in a combination thereof) either through a development of more efficient ⁺ moderators or by increasing the available activity of ⁺ particles. In this review we shall mainly concentrate on the latter approach. In atomic physics the main trust for these developments is to be able to measure differential and high energy cross-sections in e⁺ collisions with atoms and molecules. Within solid state physics high intensity, high brightness e⁺ beams are in demand in areas such as the re-emission e⁺ microscope, two-dimensional angular correlation of annihilation radiation, low energy e⁺ diffraction and other fields. Intense e⁺ beams are also important for the development of positronium beams, as well as exotic experiments such as Bose condensation and Ps liquid studies.     

Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Production of YBa2Cu3O7−x superconducting thin films by pulsed pseudospark electron beam evaporation

Thin-film superconducting YBa₂Cu₃O_7–x layers have been produced in a single-step process by pulsed electron beam evaporation from a stoichiometric 1-2-3 target. The films were produced at the 100 surface of SrTiO₃ substrates heated to a temperature of approximately 1000 K in a pure oxygen atmosphere of about 10 Pa total pressure. After deposition the films were cooled in situ within 20 minutes to ambient temperature. At present, the films are polycrystalline and show a T_c,zero of 83 K with a transition width of 3–5 K. Critical current densities of 7·10⁴ A/cm² at 4.2 K and zero magnetic field have been achieved. The pulsed electron beams used in these experiments are produced by a pseudospark discharge; the estimated energy density deposited at the target surface by the electron beam is of the order of 4 J/cm².     

New form of exploitation of cyclotron U-120

Experiments carried out on the Nuclear Research Institute cyclotron U-120 showed that the energy of the output beam can be changed in the region 6·2–7·2 MeV/nucl without additional correction of the radial slope of the magnetic field (e.g. with the use of ferromagnetic shims suitable for an energy of 6·7 MeV/nucl). Using a combination of ring and disc shims, ions of atomic hydrogen were accelerated in the energy region 8·5–10·7 MeV and ions of₃He²⁺ with energy 21 MeV. The intensities of these beams, except₃He²⁺ having been accelerated in the economical regime of the ion source, reached as much as 100 A behind the deflector. The possibility of smooth regulation of the energy without changing the classical character of the accelerator is also discussed.     

Production of high-energy electron beams in moderate and high-pressure gases

The feasibility of producing high-current, high-energy electron beams was studied for the application of nanosecond voltage pulses with amplitudes to 300 kV in accelerating gaps. The pressures of the gap gases (helium and nitrogen) measured from 10^–1 torr to atmospheric. Experiments showed that the placement of two barriers in the accelerating gap significantly increased the electron beam current due to an increase in the burn time of the volume discharge under conditions involving significant over-voltage in the electrical field. Electron beams with energies of up to 250 keV and currents up to 260 A were obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 7–9, February, 1992.     

Inclusive production of φ-mesons in neutron-proton interaction at 30–70 GeV/c

A signal of the-K⁺K^– decays has been observed in neutron-hydrogen interactions at energies of 30–70 GeV in an experiment using the BIS-2 spectrometer. The longitudinal momentum spectrum in the forward region,x _F<0·1 atp _T<1 GeV/c, can be well described by a power law dependence (1–x _F)^N withN=4·28±0·42. Thep _T ² -spectrum has been parametrized by the exp(–Bp _T ² ) law with the exponentB=(3·02±0·55) (GeV/c)^–2. The extrapolation of the measured cross section to the full kinematic region yields a value of (220±85) b in agreement with measurements from the proton beams.     

Influence of Vibrational Excitation of Triplet Molecules of Anthraquinone on the Photochemical Processes in Gas Mixtures with Amines

By the quenching of the delayed fluorescence (DF) of anthraquinone vapors by aliphatic amines (diethylamine, dibutylamine, cyclohexylamine) and pyridine the photoinduced processes proceeding with the participation of vibrationally excited triplet molecules of anthraquinone have been investigated. The DF quenchingrate constants K _q varying from 1·10⁶ sec^–1·torr^–1 in mixtures with diethylamine to 7·10³ sec^–1·torr^–1 in mixtures with pyridine have been estimated. A correlation between the values of K _q and the ionization potentials of foreign gases confirming the important role of interactions with charge transfer in the quenching of triplet molecules in the gas phase has been established. The influence of other relaxation processes on the DF quenching is considered. It is shown that the intermolecular vibrational relaxation in the T ₁ triplet state leading to the establishment of relaxation equilibrium at a vibrational temperature T _vib considerably increasing the medium temperature is the fastest process among the biomolecular processes (rate constants K _col ^V > 10⁶ sec^–1·torr^–1 > K _q). The values of T _vib and the vibrational energies E _vib of the triplet molecules after the energy exchange in the collisional complex have been estimated. It has been concluded that the photochemical reaction yield is determined by the intermolecular processes proceeding in the T ₁ state at a vibrational equilibrium characterized by high values of T _vib. The influence of E _vib of triplet molecules on the DF quenching rates at a photoinduced electron transfer is considered.     

Surface strain-hardening of iron alloys with an intense pulsed electron beam

Results are presented from study of surface strain-hardening and measurements of the structure of carbon (St. 45, U7A, 40Kh) and alloy (R6M5, Kh6VF) steels subjected to surface fusion by pulsed electron beams with the following parameters: electron energy 20–250 keV, pulse duration 5·10^–8–3·10^–4 sec, power density 10⁵–10⁹ W/cm³. It is shown that the microhardness of the surface of most alloys increases by a factor of 1.2–1.7 on quenched specimens and by a factor of 2.5–3.5 on unquenched specimens, depending on the regime. Microhardness increases in the surface layer due to quenching from the liquid state. An increase in electron energy from 40 to 250 keV with a pulse duration of 6·-10^–8 sec leads to a severalfold increase in the thickness of the strengthened layers and to a shift of the microhardness peak from the surface to a depth of 70 m. Here, microhardness reaches 2000 kgf/mm². This is due to an increase in the mean free path of the electrons in the metal and displacement of the energy-release maximum of the bundle deeper into the specimen.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 6, pp. 38–43, June, 1985.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

Experimental results of an investigation of the parameters of an artificial region of disturbance of the upper and lower ionosphere by the vertical-sounding method

Experimental results are given on an investigation of the parameters of an artificial region of disturbance (RD) of the ionosphere arising under the action on the ionosphere of strong SW radio emission (P_eq 20 MW) with a frequency of 5.75 MHz. It is shown that in this case an RD is formed in the F layer of the ionosphere with N_e/N_e 5 · 10^–2 and nonuniformities of N_e are generated or amplified. Such an RD acts as a focusing lens on probe radio waves passing through it. In the E layer of the ionosphere N_e increases by 5 · 10^–2 in about 30 sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 27, No. 1, pp. 12–17, January, 1984.     

General intense electron beams by means of a contracted arc discharge

Two types of contracted arc discharge are investigated with a view to generating intense electron beams over a wide pressure range (1–10^–3 Pa). For an arc discharge with a hollow cathode and anode, an electron beam corresponding to a current of up to 300 A and a pulse length of 25 µsec is obtained at a pressure of 1–10^–1 Pa in the accelerating gap with an accelerating voltage of up to 15 kV. At pressures of 10^–2–10^–3 Pa, emitting plasma is created by a low-pressure arc discharge on the basis of a Penning cell. Three discharge systems operating in parallel are used to increase the working life of the cathode and improve the current density distribution of the beam. An electron beam of diameter 200 mm with a current of up to 125 A and a pulse length of 50 µsec is obtained.Institute of High-Power Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshkikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 76–82, March, 1994.