Experiments on interferometric enhanced scattering in a plasma with a nonuniform magnetic field

Results are presented from the first experiments on interferometric enhanced scattering (IES) in a plasma in a nonuniform magnetic field. Measurements of the lower hybrid fluctuations of the plasma density by the IES and rf probe methods in an experimental geometry that models a tokamak configuration are found to be in satisfactory agreement. Pis’ma Zh. Tekh. Fiz. 24, 43–51 (October 26, 1998)     

Ion energy cost in a combined inductive-capacitive rf discharge

Experimental measurements were made of the ion energy cost η as a function of the parameters of a combined rf inductive-capacitive discharge at low pressures (p<10⁻² Torr). It was established that η does not depend on the power supplied, it has a minimum as a function of pressure, and also decreases when an rf potential is applied to the electrodes. The results can be used to find the optimum parameters in terms of energy efficiency of ion formation and may be useful for refining the theoretical models of a combined rf inductive-capacitive discharge. Pis’ma Zh. Tekh. Fiz. 24, 33–39 (November 26, 1998)     

Formation of macroparticle structures in an rf induction discharge plasma

It was demonstrated experimentally that macroparticles may undergo levitation and form ordered structures in an rf induction discharge plasma. The experiments were carried out using 1.87 μm melamine formaldehyde particles in neon at a pressure of 25–500 Pa. The generator frequency was 100 MHz. Pis’ma Zh. Tekh. Fiz. 24, 62–68 (October 12, 1998)     

A new type of one-dimensional discrete map

A one-dimensional two-parameter map whose behavior on the plane of control parameters qualitatively reproduces the dynamics of a flow system — an rf oscillator describable by a system of three ordinary differential equations. It is it is shown that that the behavior of the map largely coincides with that of the flow system and is also similar to the results of a previous experiment on the rf oscillator. Pis’ma Zh. Tekh. Fiz. 24, 1–8 (September 17, 1998)     

Localization of an rf capacitive discharge in a long strip line

The self-consistent problem of a an intermediate-pressure rf capacitive discharge in a long strip line is analyzed with allowance for heating of the gas. Steady-state distributions of the discharge parameters along the line are derived. It is shown that the discharge burns in certain regions, whose lengths and locations depend on the amplitude of the applied voltage. Pis’ma Zh. Tekh. Fiz. 23, 64–70 (January 26, 1997)     

Low-pressure inductive rf discharge in a rare gas-halogen mixture for economical mercury-free luminescence light sources

It is demonstrated that an inductive rf discharge in an Xe+Cl₂ mixture may be used as the active medium of an efficient, mercury-free luminescence light source. Pis’ma Zh. Tekh. Fiz. 24, 63–67 (March 26, 1998)     

The “zero” current and self-sustaining electron bunches in M-type devices

When the processes occurring in the entire interaction space of a magnetron device are included simultaneously in a numerical simulation it is possible to observe the onset and behavior of stable solitary electron bunches. It is shown that these self-sustaining electron bunches may be responsible for the existence of an anode current in the absence of rf interaction. Pis’ma Zh. Tekh. Fiz. 24, 57–62 (June 26, 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)     

Determination of electron transport coefficients in argon from ignition curves of rf and combined low-pressure discharges

Ignition curves of rf and combined (rf+static electric field) low-pressure discharges are used to determine the electron drift velocity V _dr in the range E/p≈70−2000 V/(cm·Torr) and the ratio of the longitudinal diffusion coefficient to the electron mobility D _L /μ _e in the range E/p≈ 1−2000 V/(cm·Torr). Pis’ma Zh. Tekh. Fiz. 24, 49–55 (April 26, 1998)     

Self-consistent model of a low-pressure rf capacitive discharge

A simple self-consistent model of a low-pressure rf capacitive discharge is formulated. Effects associated with stochastic heating of the electrons and the nonlocal nature of the electric field are taken into account. The relations obtained can be used for a qualitative analysis of the main features of these low-pressure discharges. The results of the numerical calculations show good agreement with available experimental data. Pis’ma Zh. Tekh. Fiz. 23, 39–45 (January 12, 1997)     

Growth of GaN by molecular-beam epitaxy with activation of the nitrogen by a capacitive rf magnetron discharge

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (June 26, 1998)     

Modified method of plasma-enhanced chemical vapor deposition of nanocrystalline silicon

A modified plasma-enhanced chemical vapor deposition technology is developed for nanocrystalline Si which combines the standard rf glow discharge method and the hollowcathode discharge method in a single process cycle. The volume fraction of nanocrystallites varied monotonically along the layer, whereas their size remained constant. The electrical and optical characteristics of these films were investigated. Pis’ma Zh. Tekh. Fiz. 24, 26–30 (October 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)     

Induced of zeeman coherence in an ensemble of cesium atoms interacting with a two-frequency (microwave+rf) magnetic field

Interference between Zeeman states corresponding to the forbidden magnetic-dipole transition ΔF=0, Δm _F=2 is reported in connection with the simultaneous interaction of 6² S _1/2 cesium atoms with a resonant microwave field and an rf field which varies at twice the Larmor frequency and is directed perpendicular to a static magnetic field H ₀=0.2 Oe. Pis’ma Zh. Tekh. Fiz. 24, 89–93 (July 26, 1998)     

Electronic energy spectrum of the sheath of an asymmetric low-pressure capacitive rf discharge

The high-energy part of the electron energy spectrum of the plasma of an asymmetric capacitive low-pressure rf discharge in air associated with electron beams near the electrodes is studied experimentally. It is found that the energy distributions obtained under different conditions contain a beam peak, both quasimonoenergetic and substantially broadened in energy. It is established on the basis of quantitative estimates that the substantial damping of the electron beam is due to the excitation of collisionally dissipative and collisionless beam-plasma instabilities. Pis’ma Zh. Tekh. Fiz. 25, 32–39 (October 12, 1999)     

The “negative trapping” effect in the magnetic-field dependence of absorption in high-temperature superconductors

This paper reports the first study of the absorption of an rf electromagnetic field in high-temperature superconducting samples of YBa₂Cu₃O_7−x in the range of magnetic fields corresponding to the onset of the “negative trapping” effect. It is shown how additional annealing and degradation of the sample influence the onset of the effect. A modification of the model of dynamic interaction of superconducting loops is used to explain the observed phenomena. Pis’ma Zh. Tekh. Fiz. 23, 20–25 (March 26, 1997)     

Sealed efficient excilamps excited by a capacitive discharge

The development of sealed XeCl (λ∼308 nm), KrCl (λ∼222 nm), and XeI (λ∼253 nm) excilamps excited by a capacitive rf discharge is reported. It is shown that highly efficient emission of exciplex molecules is achieved under capacitive discharge excitation and the emitter has a simple design. An average emission power of 3W was obtained with a ∼12% efficiency and the lifetime of the sealed excilamps was longer than 1000 h. Pis’ma Zh. Tekh. Fiz. 25, 27–32 (November 12, 1999)     

Mass spectroscopic measuring of SiCl<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 0–2) radicals in SiCl<Subscript>4</Subscript> RF glow discharge plasma

The relative densities of SiCl _n (n = 0–2) in SiCl₄ radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, i.e., rf power, discharge pressure, substrate temperature, and SiCl₄ flow rate on the relative densities of SiCl _n (n = 0–2) are investigated in detail. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature, and low flow rate), which enhanced the formation of SiCl _n (n = 0–2) radicals, is searched by a great deal of measurements and discussions. In the optimum configuration of discharge parameters, we measure the spatial distribution of SiCl _n (n = 0–2) radicals in the most optimized plasma parameters. The experimental results reveal that Si and SiCl may be the dominant precursors in forming the thin film.     

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)     

Observation of anomalous transmission of x-rays in tungsten single crystals

Results of observations of the anomalous transmission of x-rays in tungsten single crystals are presented. The dislocation density (2–4)×10⁵ cm⁻² was determined from an analysis of the dynamic diffraction characteristics. Pis’ma Zh. Tekh. Fiz. 25, 16–21 (December 12, 1999)