Physical model of the influence of oversize impurities on the radiation hardening of iron α-alloys

A physical model is proposed for the influence of oversize impurities on the characteristics of radiation-defect formation in neutron-irradiated iron alloys at low and high irradiation temperatures. A comparison is made between the theoretical expressions obtained for radiation hardening at different temperatures and the existing experimental data. For low temperatures, the agreement was satisfactory, so we can estimate one of the microscopic parameters of impurity atoms — the relative size of the region of influence of the impurity atoms. Pis’ma Zh. Tekh. Fiz. 23, 77–83 (April 26, 1997)     

Structure of a picosecond electron beam inside a vacuum diode

The structure of a picosecond (∼150 ps) electron beam in the cathode-anode gap of a vacuum diode is determined. The electron beam is modeled in the form of flat quasiparticles with a definite charge density which follow one after another in equal time intervals. It is shown that the expansion of concentric layers of the beam under the action of the electric and magnetic self-fields strongly depends on the current strength. The experimental confirmation of the computed estimates is illustrated by recording the structure of the electron beam at the anode using a film which is sensitive to electron radiation. Pis’ma Zh. Tekh. Fiz. 25, 39–45 (September 26, 1999)     

Self-similarity and branching of wavelet transforms of microwave signals generated by a vircator

The turbulence regimes of an electron flow with a virtual cathode are studied. The microwave signals generated by a vircator are calculated by the method of large particles. The wavelet transforms of these signals are constructed, and it is shown that they have a complicated self-similar and branching structure. It is concluded that the turbulence of an electron flow is caused by macroscopic instabilities. Pis’ma Zh. Tekh. Fiz. 22, 92–96 (December 26, 1996)     

Influence of a shock-wave pressure gradient on the appearance of a microhardness maximum in α-Fe irradiated by a high-power ion beam

The results of research on the defect structure and microhardness in α-Fe irradiated by a pulsed high-power ion beam are presented. The results are obtained with the use of positron annihilation, electron microscopy, and a nanoindenter. It is shown that the pressure gradient and the depth of formation of the shock wave front in α-Fe irradiated by a high-power ion beam have an influence on the formation and location of the maximum of the dislocation density and microhardness in the modified layer. Pis’ma Zh. Tekh. Fiz. 24, 72–77 (October 26, 1998)     

Influence of substrate thickness on plasma resonance in a semiconductor heterostructure with a two-dimensional electron gas

A strict electrodynamic approach is used to analyze the excitation of oscillations of a two-dimensional electron plasma by an external plane electromagnetic wave in a semiconductor heterostructure with a grating coupling element. An analysis is made of the influence of the substrate thickness on the resonance magnitude and the profile of the resonance curve. Pis’ma Zh. Tekh. Fiz. 24, 70–74 (May 12, 1998)     

Formation of dense electron beams in a gun with a plasma anode based on a reflecting discharge

A method of obtaining low-energy, high-current electron beams in a gun with a plasma anode based on a reflecting discharge is proposed and implemented for the first time. Pis’ma Zh. Tekh. Fiz. 23, 42–46 (May 26, 1997)     

Scenario for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator

A 2.5-dimensional particle-in-cell code was used to simulate different scenarios for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator. Vircators with and without anode foils were compared. It was found that the squeezed state is established in both cases but the dynamics of establishment differ. Pis’ma Zh. Tekh. Fiz. 23, 29–33 (November 26, 1997)     

Čerenkov superradiance from a subnanosecond electron bunch in a sectional decelerating system

Induced coherent radiation (superradiance) from a subnanosecond electron bunch in a combined decelerating system has been investigated experimentally. In a first section formed by a periodically modulated waveguide, the density of the bunch is modulated and it then radiates in a second section formed by a waveguide partially filled with a dielectric. At an electron energy of 250 keV and a peak current of 800 A, millimeter radiation pulses with powers up to 2 MW and lengths up to 800 ps were obtained. Pis’ma Zh. Tekh. Fiz. 23, 14–19 (December 26, 1997)     

Possible transport of an electron beam with above-limit current in a vacuum channel with plasma partitions

Computer modeling by the particle-in-cell method is used to demonstrate that a high-current electron beam with an above-limit current can be transported in a vacuum channel with plasma partitions, whereas without these partitions a virtual cathode forms, blocking the channel. Pis’ma Zh. Tekh. Fiz. 24, 86–90 (February 12, 1998)     

Induction self-acceleration of a high-current electron beam

Computer modeling using the particle-in-cell method confirmed that self-acceleration by induction of a high-current relativistic electron beam predicted by G. A. Askar’yan [At. énerg. 6, 658 (1959)] may occur when this beam passes through a thick diaphragm containing an aperture. Pis’ma Zh. Tekh. Fiz. 25, 52–56 (July 26, 1999)     

Density distribution of a two-dimensional electron gas in a semiconducting heterostructure with a periodic gate electrode

Calculations are made of the electron density distribution profiles in a layer of two-dimensional electron gas in a semiconducting heterostructure when reference and reverse potential biases are applied simultaneously to neighboring stripes of a periodic gate electrode. It is shown that for the structure parameters used experimentally the density distribution profile differs appreciably from rectangular and from sinusoidal. Pis’ma Zh. Tekh. Fiz. 25, 37–41 (January 12, 1999)     

Conversion of the polarization of an electromagnetic wave under cyclotron resonance in a two-dimensional electron system

A theoretical analysis is made of the conversion of the polarization of an electromagnetic wave when cyclotron resonance is excited in a two-dimensional electron system. It is shown that the greatest conversion of the polarization can be achieved in the reflected wave. At high electron concentrations the effect remains very appreciable even in the presence of electron scattering. In this case, the wave polarization conversion effect can be used to obtain information on electron relaxation in a two-dimensional system. Pis’ma Zh. Tekh. Fiz. 25, 21–26 (November 12, 1999)     

Influence of the parameters of a pulsed electron beam on the removal of nitrogen oxides from flue gases

Results are presented of an experimental investigation of the oxidation of small quantities of nitrogen oxides in air irradiated by a pulsed electron beam. It is shown that the impurity removal process is strongly influenced by the pulse length and current density of the electron beam. It is noted that an adequate model is needed to describe the plasma-chemical oxidation processes of nitrogen oxides involving charged and excited particles. Pis’ma Zh. Tekh. Fiz. 24, 47–50 (August 12, 1998)     

Growth of cubic GaN by molecular-beam epitaxy on porous GaAs substrates

It is shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge. The resulting undoped epitaxial layers possessed ntype conductivity with a carrier concentration ∼10¹⁸. Data obtained by scanning electron microscopy and cathodoluminescence indicate that at thicknesses ∼2000 Å, continuous layers of the cubic GaN modification are obtained regardless of the substrate orientation. Pis’ma Zh. Tekh. Fiz. 25, 3–9 (January 12, 1999)     

Formation of macroparticle charge in a classical Coulomb plasma

An expression is derived for the average macroparticle charge and the electron temperature in a heated dense gas. Pis’ma Zh. Tekh. Fiz. 25, 52–55 (January 12, 1999)     

Ion accelerator with space-time modulation of a relativistic electron beam

An analysis is made of a possible method of collective ion acceleration by combining spatial modulation of the electron beam potential with temporal modulation of the current. A conceptual design is proposed. Pis’ma Zh. Tekh. Fiz. 24, 74–78 (September 26, 1998)     

Influence of feedback on the complex dynamics of an electron beam with a virtual cathode in a virtode

Results are presented of a numerical simulation of the nonlinear dynamics of a relativistic electron beam with a virtual cathode in a drift relativistic-electron-beam vircator system with and without external feedback. Pis’ma Zh. Tekh. Fiz. 24, 51–57 (March 12, 1998)     

High-power HF laser pumped by an electron-beam-initiated chemical nonchain reaction

The development of a high-power HF laser pumped by a chemical nonchain reaction initiated by a radially converging electron beam is reported. A radiation energy of ∼ 115 J with an efficiency of ∼ 8% in terms of deposited energy has been achieved in a mixture with an active volume of ∼ 30 liters. It is shown that because of the high SF₆ density, the total pressure jump in SF₆–H₂(D₂) mixtures caused by the electron beam injection and the chemical reactions is several times smaller than that in the active mixtures of exciplex lasers for the same input energies. This factor considerably facilitates the development of wide-aperture HF and DF lasers with an SF₆ fluorine donor pumped by an electron-beam-initiated chemical nonchain reaction. Pis’ma Zh. Tekh. Fiz. 23, 58–64 (March 12, 997)     

Heating of a current filament and formation of constrictions in a pulsed vacuum discharge

It is shown that a rapid current rise in a pulsed vacuum discharge is accompanied by enhanced compression of the current filament by its self-induced magnetic field. As a result, a constriction forms at a distance L≃1 mm from the cathode and the electron temperature increases to 10²–10³ eV at currents of order 1 kA. This behavior explains the observed increase in the degree of ion charge and the appearance of x-rays as the current pulse length decreases. The criterion for a rapid rise is the condition τ<L/V≃10⁻²⁷ s, where τ is the characteristic current amplification time and V≃10⁶ is the velocity of the cathode plasma. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (September 26, 1998)     

Possibility of using a large orbit regime for operation at bounce-frequency harmonics in a free-electron maser with a guiding magnetic field

It is suggested that a free-electron maser based on the LIU-3000 accelerator (Joint Institute for Nuclear Research, Dubna) can be made to emit in the short-wavelength part of the microwave range by using radiation at harmonics of the bounce frequency of an electron beam propagating along a helical trajectory with a large gyration radius on the transverse inhomogeneity scale of the rf field and selectively exciting a cylindrical waveguide mode whose azimuthal index is equal to the number of the harmonic. Pis’ma Zh. Tekh. Fiz. 25, 30–36 (January 12, 1999)