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.     

Generating a low-energy high-current electron beam in a gun having a plasma anode

Research has been done on major physical processes governing the scope for generating magnetized low-energy high-current electron beams in a plasma-filled system. Conditions are considered for efficient excitation of the explosive electron emission at a large-area cathode at low accelerating voltages, together with the trends in beam formation in the nonstationary double layer formed between the cathode and anode plasmas, as well as the beam transport to the collector in the inhomogeneous guiding plasma. It is found that a gun having a plasma anode enables one to generate wide-aperture electron beams of microsecond duration having a mean electron energy of 10–20 keV and an energy density of up to 20 J/cm² or more, which goes with homogeneity sufficient for technological purposes.High-Current Electronics Institute, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh, Fizika, No. 3, pp. 100–114, March, 1994.     

Schlieren diagnostics of pulsed electron beam ablation of polymethyl-methacrylate

The investigation of the interaction of pulsed electron beams with PMMA (polymethylmethacrylate) targets is reported. The electron beam of some 10^–8 s in duration is produced in a pulsed low-pressure gas discharge. The beam power density of up to 10⁸ W/cm² leads to a surface plasma formation similar to that of the pulsed laser ablation process. The propagation of the ablated material and the shock wave inside the PMMA target are observed by means of Schlieren diagnostics. An electron density gradient of over 3×10¹⁹ cm^–4 has been observed in the expanding plasma up to 1.5 s after the plasma formation. During the early stage of expansion, the expansion velocity of the plasma plume as determined by the steep electron density gradient is around 10⁵ cm/s. The pressure behind the shock front inside the PMMA target as determined from the shock velocity exceeds 0.3 Gpa.     

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.     

Controlled discharge in a vacuum gap switched by 1 Mc current pulses of up to 150 kA

The firing delay time, the rise time of the current up to its maximum, and the primary current amplitude of a controlled discharge in a vacuum gap are considered, for a voltage range of 10–80 kV, with a residual gas pressure in the chamber of 10^–4–10^–5 mm of mercury. The gap is switched by a damped oscillatory current pulse with a frequency of 1.25 Mc and a maximum amplitude of about 150 kA. The discharge is started by either one or three triggering devices.     

Formation of high-energy electron beams in gases of different densities

An investigation was made of the formation of beams of fast electrons in different gases at pressures of from 0.01 to 100 kPa. Plots were made of the dependences of the electron beam currents I_e on the gas pressure p for different electric field strengths E. The dependences I_e=f(p) for air were found to intersect the similar dependences for other gases (helium, nitrogen, neon, and argon) at a pressure of p=10.6 kPa and for E=2.3·10⁵ V·cm^–1. This fact is explained by the influence of the oxygen ions and atoms on the electron beam formation process. Another experimental result, the appearance of a minimum in the dependences I_e=f(p) for all gases, is explained by defocusing of the electron beam, the appearance of a reverse current, and magnetic neutralization of the beam. Electron beams were obtained having a pulse duration of 15–20 nsec and a current of 10⁵-10⁶ A/m² per unit cathode area.Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 67–70, June, 1993.     

Neutralizing a high-aperture metal-ion beam

It is found that secondary electrons ejected by the ions from the collector are responsible for neutralizing 300 sec pulses of wide-aperture ion beams (about 100–300 cm²) formed by various metals and having current densities ji of about 10^–2 A/cm² and energy _i 100 keV. A negative potential _ee=–500 V applied to the extracting electrode relative to the grounded collector improves substantially not only the beam neutralization in the transport section but also the ion generation efficiency in the accelerating gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 53–56, April, 1990.     

Generation of Electron Beams in the Range of Forevacuum Pressures

This paper presents the results of a study on the generation of electron beams at gas pressures ranging from 0.01 to 0.1 Torr. The fact that this range of pressures is attainable with mechanical pumps only has provoked interest in this problem. To generate an electron beam, use is made of a plasma source based on a hollow-cathode discharge in combination with a plane-parallel acceleration gap. In the given range of pressures, the peculiarities of emission and acceleration of electrons are related to the high probability of ionization of the gas in the acceleration gap and to the formation of an ion flow propagating toward the electron beam. This causes a decrease in discharge operating voltage and also an increase in plasma density in the emission region. Two types of breakdown are observed in the acceleration gap: an interelectrode breakdown and a breakdown in the plasma–electrode system. The designed electron source allows one to obtain beams of cylindrical cross section with currents of up to 1 A and energies of up to 10 keV.     

Anomalous changes in the properties of tellurium-doped indium arsenide single crystals

The change in the main parameters of indium arsenide with the introduction of tellurium is considered from weak doping to concentrations corresponding to the solubility limit. Analysis of the experimental data shows that the functional dependence on the electron density of the band gap width, the Fermi energy, the magnitude of background absorption, the parameter characteristic of the carrier scattering mechanism has a discontinuity at N=(3–5) · 10¹⁸ cm^–3. The observed phenomena are explained by the redistribution of component atoms of the system between sublattices with the formation of an ordered phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 51–57, May, 1984.     

Electron traps in wide-gap n-Hg0.3Cd0.7Te characterized by time-resolved photoconductivity

Time-resolved photoconductivity measurements have been used to characterize electron traps in wide-gap n-HgO_0.3Cd_0.7Te for the first time. The characterization was made possible by combining the time-resolved photoconductive data with the analytical method conventionally used in DLTS spectroscopy. Two electron traps were found in the band gap with 61 meV and 79 meV below the conduction band edge, their concentrations are 1.1×10¹³ cm^–3 and 5.8×10¹¹ cm^–3, respectively. Compared with DLTS spectroscopy, this characterization method markedly simplifies sample preparation and experimental procedure.     

Electron-optics study of the development of an electric discharge in a gas at high-electric field intensities and with one-electron ignition

A study was made of the luminous region in a discharge gap with copper electrodes, a field of E = 80 kV/cm, air at atmospheric pressure, and a gap width of 4 or 2 mm. The cathode was irradiated with a spark to ignite the initial electrons. The electron current from the cathode was 0.2 · 10⁹ electrons/sec. The exposure time per frame was 3 · 10^–9 sec. With a gap width of = 4 mm, a luminous region is observed at the cathode 2 nsec after voltage is applied to the gap; this region propagates toward the anode, simultaneously increasing in diameter, at a velocity of 10³ cm/sec. A voltage drop is established across the gap approximately 0.5 nsec after the luminous front arrives at the cathode. In narrower gaps, the voltage drop is established across the gap a considerable time after the luminous region has crossed the gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 24–27, November, 1969.     

Design of multiple layered a-Si:H(F)/a-SiGex:H(F) films for enhancement in photoresponse in the near-infrared spectrum

Photo-electric properties of a-Si:H(F)/a-SiGe_x:H(F) multilayer films were investigated by measurements of optical absorption, and photoconductivity in both steady and transient modes with the repetition length and the difference in the optical gap between a-Si:H(F) and a-SiGe_x:H(F) as the variables. Measurements of primary photocurrent clarified that photosensitivity for the multilayer films extended to longer wavelengths of around 725 nm, while high resistivity was maintained despite of lowering the band gap.The drift mobility of electrons was measured by the time-of-flight technique, showing 10^–2-10^–3 cm²/Vs, while the drift mobility-lifetime products of electron was maintained to be 10^–7 cm²/V. On the other hand, the drift mobility of holes was 10^–3 cm²/Vs, which was the similar magnitude to that of a-Si:H(F).     

Effect of electron irradiation on creep and dislocation structure of aluminium

The effect of electron irradiation and strain on structure of technical-purity aluminium subjected to constant-load tensile creep tests was investigated. The dislocation structure was statistically analyzed. The effect of electron irradiation appears in the creep rate reduction and generation of radiation defect clusters, the density of which is approximately proportional to the dose. The effect on the dislocation distribution is dependent on the dose as well. Doses1·2×10¹⁷ cm^–2 speed up the formation of a polygonal structure characterizing the steady-state creep.     

Ionic Synthesis of Ga1–x In x As Solid Solution Films

The Ga_1–x In _x As compound obtained by In-ion implantation (100 keV and (0.45–6)·10¹⁷ cm^–2) followed by thermal (800 °C and 15') or high-energy electron-beam (1 MeV, 0.6 mA·cm^–2, 660 °C, and 16 s) annealing is investigated by Rutherford backscattering, optical absorption, and capacitor photoelectromotive force. It is shown that x increases from 0.07 up to 0.21, and the band gap decreases from 1.34 down to 1.21 eV as the implantation dose increases. The surface potential decreases from 0.79 down to 0.58 V. A high efficiency of electron-beam annealing is pointed out.     

Low energy ion beams by laser interaction

We developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity. The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analysed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm². The peak of current density was 3.9 and 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be 10¹² ions/cm². Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad.     

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.     

The factor of nonparaxial Hermite–Gaussian beams and related problems

On the basis of the second-order moment of the power density and in the use of the series expansion, the expressions for the beam width, far-field divergence angle and M² factor of nonparaxial Hermite–Gaussian (H–G) beams are derived and expressed in a sum of the series of the Gamma function. The theoretical results are illustrated with numerical examples. The M² factor of nonparaxial H–G beams depends not only on the beam order m, but also on the waist-width to wavelength ratio w₀/λ. The far-field divergence angles of nonparaxial H–G beams with even and odd orders approach their upper limits θ_max=63.435 and 73.898, respectively, which results in M²<1 as w₀/λ→0. For the special case of m=0 our results reduce to those of nonparaxial Gaussian beams. Some problems related to the characterization of the nonparaxial beam quality are also discussed.     

Independent UHF plasma source and possibility of filling open magnetic trap

A stationary UHF plasma source, its characteristics and possibility of filling open magnetic trap with plasma injected from it have been described. Plasma is created in the source at frequency of 2400 MHz (supplied power is up to 150 W) in the electron cyclotron resonance (ECR) regime under working gas pressure 10^–5–10^–2 Torr. By changing discharge conditions one can change the injected plasma density from 10⁹ to 10¹² cm^–3, at the temperatureT _e=2–10 eV. The possibility of efficient plasma injection from the source into the open magnetic trap of various configurations is shown experimentally. Plasma characteristics in the trap are presented under various experimental conditions. It is established that plasma parameters can be easily changed in the trap.     

Estimation of the energy spectrum of cosmic ray electrons at the atmospheric depth (3.8–7.4)g.cm−2

Analytical calculations have been done to estimate the energy spectra of the secondary electrons originated from the decay of charged and neutral pions initiated on the upper atmosphere from the primary nucleon–air interactions in the energy range (4–100) GeV. The calculations are valid up to an atmospheric depth of about (3.8–7.4) g.cm^–2. The derived results are compared with the observed electron fluxes available from the balloon flight experiments of MASS2, HEAT, magnetic spectrometer system of Golden et al., instrument using scintillating fibers of Nishimura et al., and BETS.     

The optical gap of NiO

The nature of the optical absorption gap in NiO at 4.0 eV is investigated. It is found that this gap is due to a band to band transition, where an electron is taken out of the valence band and placed into the conduction band. The optical gap of 6.0 eV found in NiMgO is of a nature, where an electron is taken out of the oxygen 2p band and placed into the first affinity level of the Ni²⁺ ion (3d ⁸L»3d ⁹L^–1). The impurity band created in Ni_1–x Li _x O by the Li ions is found 2.3 eV below the bottom of the conduction band in agreement with model predictions.