Near field of a loop antenna operating in plasma in the whistler frequency range

The structure of the RF magnetic field in the vicinity of a loop antenna operating in the whistler frequency range has been studied experimentally and theoretically. The experiments were performed over a wide frequency range at different values of the plasma density, electron temperature, and ambient magnetic field strength. It is shown that, when a loop antenna is smaller than the wavelength of a quasi-longitudinal whistler, the structure of the magnetic field of such an antenna is nearly the same as that of the field of a current-carrying loop in vacuum; otherwise, the RF field is localized near the antenna wire. The results of numerical calculations agree with the measured field distributions. The antenna field is calculated by expanding it in the eigenmodes of a magnetized plasma with allowance for not only propagating but also nonpropagating (exponentially decaying) waves, which make the main contribution to the near field. An analytic estimate of the depth to which the RF magnetic field of a loop antenna penetrates into the plasma is obtained.     

Characteristic properties of the frame-antenna-produced RF discharge evolution in the Uragan-3M torsatron

In the ? = 3 Uragan-3M torsatron, hydrogen plasma is produced and heated by RF fields in the Alfvén range of frequencies (ω ? ω _ci ). To this end, a frame antenna with a broad spectrum of generated parallel wavenumbers is used. The RF discharge evolution is studied experimentally at different values of the RF power fed to the antenna (the anode voltage of the oscillator and the antenna current) and the initial pressure of the fueling gas. It is shown that, depending on the antenna current and hydrogen pressure, the discharge can operate in two regimes differing in the plasma density, temperature, and particle loss. The change in the discharge regime with increasing anode voltage is steplike in character. The particular values of the anode voltage and pressure at which the change occurs are affected by RF preionization or breakdown stabilization by a microwave discharge. The obtained results will be used in future experiments to choose the optimal regimes of the frame-antenna-produced RF discharge as a target for the production and heating of a denser plasma by another, shorter wavelength three-half-turn antenna.     

Plasma control of the directional pattern of a multislot waveguide antenna

The possibility of controlling the directional pattern of a multislot waveguide antenna with the help of a gas-discharge tube placed inside the waveguide was studied experimentally. Since the dielectric parameters of the waveguide depend on the plasma density in the discharge column, they can be controlled by varying the discharge current. The high efficiency of such plasma control was demonstrated experimentally: as the discharge current was varied from 0 to 200 mA, the antenna directional pattern turned by ～17°.     

Diagnostics of a magnetized plasma by the field of surface waves guided by a discharge channel

A diagnostic method for determining plasma density from the dispersion of surface waves guided by a discharge channel in an axial magnetic field is discussed. The diagnostic characteristics that are the easiest to record experimentally are determined by analyzing the theoretical dispersion curves, and the ways of exploiting these characteristics for plasma diagnostics are suggested. To determine the slowing-down factor of a probing wave in a plasma channel, it is proposed to use diagnostic-signal resonances that occur when the wavelength of the slowed wave becomes equal to the length of the emitting or receiving antenna. The dependence of the plasma density averaged over the cross section of the plasma column on the strength of the external magnetic field is determined for a discharge channel formed as a result of the ionization self-channeling of plasma (lower hybrid) waves and whistlers.     

Surface microwave discharges in air

A microwave discharge excited on the outer surface of a dielectric antenna has been investigated. The transverse and longitudinal dimensions and propagation velocities of the discharge have been measured as functions of the air pressure and the power and duration of the exciting microwave pulse. The spatial distributions and time evolution of the gas temperature, electron density, and radiation intensity of the discharge have been determined. It is shown that the degree of ionization of the discharge plasma can exceed 10%. The spatial distribution of the electron density is found to depend strongly on the air pressure.     

Numerical simulation of the electromagnetic fields excited by loop antennas in plasma in the whistler frequency range

The electromagnetic fields excited by circular loop antennas in a magnetized plasma in the whistler frequency range are simulated by the finite-difference time-domain method. The spatial structure of quasi-monochromatic fields excited in the near- and far-field zones by an antenna with a harmonic current, as well as the dynamics of the electromagnetic field excited by an antenna with a current in the form of a single video pulse, is studied. Simulations performed for a uniform plasma and uniform ambient magnetic field agree well with the results of theoretical analysis and model laboratory experiments performed on large-scale plasma devices.     

Investigation of plasma characteristics in an unbalanced magnetron sputtering system

Results are presented from experimental studies of a magnetron sputtering system for different configurations of the magnetic field above the cathode surface. The current-voltage characteristics of a magnetron discharge at different working gas pressures (0.08–0.3 Pa) and currents in the unbalancing coil were studied. The production and transport of charge carriers in a magnetron discharge with an unbalanced magnetic field was investigated by means of probe measurements of plasma characteristics and ion energies in the region between the substrate and the magnetic trap at the cathode surface. The radial distributions of the ion current density, plasma potential, and floating potential in the unbalanced operating mode are found to have pronounced extrema at the magnetron axis. It is shown that the plasma density near the substrate can be increased considerably when the axial magnetic field is high enough to efficiently confine plasma electrons and prevent their escape to the chamber wall.     

Plasma asymmetric dipole antenna excited by a surface wave

A study is made of a quarter-wave asymmetric dipole antenna in which the conducting rod is replaced by a plasma column with an electron density much higher than the critical density. The parameters of such an antenna are determined by the exited surface wave, which affects the electromagnetic field structure in the near-field zone. It is shown analytically, numerically, and experimentally that the resonant length of the plasma dipole antenna is close to one-quarter of the length of the surface wav and that the conversion efficiency of plasma antenna power into radiation can be no worse than that of a metal dipole antenna. It is also shown experimentally that the plasma in a dipole antenna can be self-consistently excited by an RF oscillator and that the excited RF oscillations can be efficiently radiated into the surrounding space.     

Helicon plasma in a nonuniform magnetic field

The distributions of the electron density in a plasma produced by helicon waves and the correspond-ing wave amplitudes and phases are studied experimentally. The measurements were carried out in an argon plasma at a pressure of 3 mtorr and at an input RF power of up to 600 W. The magnetic field was caried in the range from 0 to 200 G. The efficiency of plasma production in both uniform and nonuniform fields is investigated. It is shown that, in a nonuniform magnetic field, the electron density can be substantially increased (up to 5×10¹² cm^?3) by placing an antenna in the region in which the magnetic field is weaker than in the main plasma.     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Double layer in a cylindrical hollow-cathode discharge

A dc cylindrical coaxial glow discharge with an inner grid anode has been studied. The region between the two electrodes is seen dark, while a brightly glowing region forms inside the grid anode up to the center. The current-voltage characteristic of a dc cylindrical glow discharge in nitrogen is similar to that of a normal glow discharge, while the normal glow discharge voltage decreases with increasing pressure. The minimum plasma potentials are observed in the hollow cathode region due to the accumulation of electrons at the back of the grid anode. At the center, some of the passed electrons are converged, so their potential is decreased. These electrons have a sufficient time to be redistributed to form one group with a Maxwellian electron energy distribution function. The electron temperature measured by electric probes varies from 1.6 to 3.6 eV, while the plasma density varies from 3.9 × 10¹⁶ to 7 × 10¹³ m⁻³, depending on the discharge current and probe position. The plasma density increases as the electrons move radially from the grid toward the central region, while their temperature decreases.     

Diagnostics of plasma oscillations by the field of surface waves guided by a dielectric waveguide

The potentialities of the diagnostic method for determining the plasma parameters by recording the surface waves guided by a dielectric waveguide and scattered by plasma oscillations are discussed. The use of surface (slowed) waves makes it possible to improve both the sensitivity and spatial resolution of measurements. The scattering is the most intense near the waveguide cutoff, at which the dependence of the wave propagation constant on the plasma density is the steepest. It is shown experimentally that the method proposed makes it possible to determine the discharge plasma density and electron energy and to estimate the amplitude of the RF field of the plasma waves forming the discharge and the amplitude of plasma density oscillations in these waves. The data obtained from the measurements of the amplitudes of both high-and low-frequency plasma density oscillations by the proposed method agree satisfactorily with theoretical predictions. The experimental data on the plasma density are confirmed by other diagnostic measurements. The ways of reducing measurement errors are proposed.     

Properties of a low-pressure inductive RF discharge I: Experiment

Results are presented from experimental studies of low-pressure inductive RF discharges (including those with a capacitive component) employed in plasma technology. It is shown that both the RF power absorbed in the plasma and the electron density depend nonmonotonically on the external magnetic field. Discharge disruptions occurring at critical values of the magnetic field and the spatial redistribution and hysteresis of the plasma parameters were observed when varying the magnetic field and RF generator power. The parameters of the plasma of low-pressure (0.5–5 mTorr) inductive RF discharges were investigated, and the discharge properties related to the redistribution of the RF generator power between the plasma and the discharge external circuit were revealed. The experiments were performed with both conventional unmagnetized inductive plasma sources and plasma sources with a magnetic field.     

Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system

Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.     

Emission Efficiency and Amplification Properties of the Plasma of a Pulsed Discharge in Ar at Elevated Pressures

The spontaneous emission efficiency of an ${\rm Ar}_2^*$ excimer and its amplification properties at a wavelength of 126 nm are studied using a numerical model of the weakly ionized plasma of a pulsed discharge in Ar at elevated pressures. It is shown that, under real experimental conditions, it is possible to achieve a net gain coefficient of the active medium equal to ≈0.065 cm^?1 by increasing the gas density up to 4.0 × 10²⁰ cm^?3 at an initial gas temperature of 170 K. The internal conversion efficiency of discharge energy into spontaneous emission depends weakly on the gas temperature and attains 75% for a gas density of 2.7 × 10²⁰ cm^?3, but with excitation powers much lower than for the maximum gain. The applicability of the model at low excitation powers is tested by comparison with the experimental data.     

ECR heating of a dense plasma by helicon waves

Eigenmodes of an axisymmetric plasma column that is uniform along the magnetic field are investigated. It is shown that, as the plasma density increases, eigenmodes with frequencies close to the electron gyrofrequency tend to localize at the plasma periphery. This effect is likely to restrict the electron density at which the plasma can be heated by means of such modes. A theory is developed for the excitation of the eigenmodes of a plasma column in a weakly nonuniform magnetic field by an external antenna.     

大鼠神经源性肺水肿时交感神经放电活动,血浆儿...

Neurogenic pulmonary edema (NPE) was induced by microinjection of kainic acid into bilateral preoptic area (POA) of the hypothalamus in rats. Sympathetic discharge of the left adrenal branch was recorded, plasma catecholamine (CA) was assayed and the physical properties of pulmonary surfactant (PS) of the lung lavage were measured. The results showed that some physical properties of PS were changed in NPE, i.e. maximal surface tension (gamma Max) decreased, minimum surface tension (gamma Min) increased, recruitment index (RI), stability index and area of hysteresis loop (H-area) decreased. After injection of kainic acid into POA, the sympathetic discharge increased by 22.8 +/- 7.20% and 32.2 +/- 8.0% respectively at 30 and 60 min after injection and paralleled by a marked elevation of plasma catecholamine (CA). The results showed that PS activity had decreased at an early stage of NPE and the change of the plasma CA level was parallel to that of sympathetic discharge. It is suggested that generation of NPE may be related to some disorder of the autonomic nervous system at the level of hypothalamus, increase of sympathetic discharge, elevation of plasma CA level and fall of PS activity.     

低功率2 450 MHz射频磁场对神经元延迟整流钾通道的抑制作用

由于电子设备的广泛使用,人类已经越来越多地暴露在射频磁场的辐射下,但射频磁场的辐射效应却一直不明确．采用全细胞膜片钳技术,记录2 450 MHz射频磁场辐射对小鼠脑皮层神经元延迟整流钾电流IK的影响．利用Ansoft HFSS软件对6 dB全向天线建模仿真,验证距天线2~3 cm处磁场分布均匀,使用Agilent E5070B网络分析仪经该天线发射出2 450 MHz输出功率为39.81 mW电磁场,对细胞进行刺激．实验发现,2 450 MHz低功率射频磁场暴露5、10和15 min对IK均有明显的抑制作用;显著影响IK激活特性,对照组与磁场暴露组半数激活电压分别为（－1.13±2.32）mV和（19.52±1.03）mV(n=10, P <0.05);斜率因子分别为（23.21±3.29）mV和（13.95±1.27）mV(n=10, P <0.05)．结果表明,低功率射频磁场通过减小延迟整流钾通道电流,影响神经元的生理功能,为进一步研究电磁辐射所引发的生物学效应提供了一种新的方法．     

Reflection and transmission coefficients for radio waves incident obliquely on N identical plane plasma layers and zebra patterns in the spectrum of solar radio emission

The reflection and transmission coefficients for quasi-monochromatic radio waves incident at an arbitrary angle on an arbitrary number of identical piecewise-homogeneous plane plasma layers are calculated analytically and numerically. It is shown that alternating transparency and opacity stripes in the spectrum of radio waves passing through such a plasma structure (the zebra pattern effect) can be observed at any angle of incidence. The opacity stripes for ordinary waves are wider than those for extraordinary waves. For the zebra pattern to be well pronounced, the radio wave flux in the Sun??s atmosphere should be narrowly directed, which is possible during bursts.     

Measurements of the load resistance of a poloidal antenna and the phase velocity of fast magnetosonic waves during ICR plasma heating in the L-2M stellarator

The propagation and damping of waves excited by a poloidal antenna in a hydrogen plasma at the ion cyclotron resonance (ICR) frequency were investigated. The longitudinal wavenumber and damping length of waves excited in the ohmically heated plasma of the L-2M stellarator, the dependence of the damping length of fast magnetosonic waves on the magnetic field strength, and the dependence of the antenna load resistance on the plasma density were measured. It is the first time that such complex measurements were performed in experiments on ICR heating of a hydrogen plasma at the fundamental harmonic of the ion gyrofrequency in toroidal magnetic confinement systems.