High Frequency Electric Field Research Articles

The effect of an inhomogeneous high frequency electric field on the parameters of a helium-neon laser

The effect of an inhomogeneous high frequency electric field on the parameters of a helium-neon laser

Biophysical aspects of dielectrophoresis

Dielectrophoresis, the translational motion produced by the action of a nonuniform electric field upon neutral polarizable bodies, is proving useful in handling biological systems. It is especially useful in studies of suspensions of cells. Normal and abnormal cells respond differently, and may be separated on the basis of their differing polarizational response. Because the phenomenon depends upon the polarization and not upon the charge of the particles, subtle new differences are available for exploitation by dielectrophoresis. Operation can be carried out in a high frequency electric field. The frequency “spectrum” of cellular response to dielectrophoresis varies with the species, and with the physiological state of the individual cell. Cells may be studied individually or in large numbers at a time. Cells may be gathered and formed into “fleshlike” aggregates using dielectrophoresis.

Particle Motion in Magnetic Mirrors with High-Frequency Electric Field Fluctuations

Particle motion in a magnetic mirror containing high-frequency short-wavelength longitudinal electric fields is followed numerically for many mirror bounce periods. It is found that while the magnetic moment undergoes large rapid changes, these fluctuations seldom imply rapid particle loss from the mirror. This behavior is shown to be completely consistent with nonlinear superadiabatic theory, wherein containment properties of the trap are affected only when particles cross isolated singular surfaces in phase space.

Molecular Orientation Effects in Compensated Liquid Crystals

An optical and a dielectric memory effect is observed in compensated mixtures of cholesteryl chloride and cholesteryl laurate. When the temperature is increased after a sufficiently high dc electric field is once applied and then reduced to zero at low temperatures, the liquid crystal becomes transparent and the dielectric constant becomes maximum at a temperature approaching the cholesteric to nematic phase transition temperature. This effect can be erased by heating up to an isotropic state. The phase transition from the homeotropic to the plane texture is observed by applying the high frequency electric field. The critical frequency depends upon the sample temperature and it varies from 3 kHz to 500 kHz as the temperature rises from 17°C to 50°C. These phenomena are discussed based on the orientation effects of liquid crystal molecules.

Parametric Instability of Plasma Waves in a Magnetic Field, Due to High-Frequency Electric Fields

We have observed experimentally the parameteric excitation of ion acoustic waves and cyclotron harmonic waves by a high-frequency electric field with frequencies near the harmonics of the cyclotron frequency. We have verified both the wave-vector and the frequency selection rules. The measured threshold fields and growth rates are in good agreement with theory.

Erratum: “Effects of a High-Frequency Electric Field on Micro-Instabilities Driven by Density Gradient”

Erratum: “Effects of a High-Frequency Electric Field on Micro-Instabilities Driven by Density Gradient”

Interactions between Ion Waves and a High-Frequency Electric Field

The properties of ion waves in a high frequency electric field are studied. The modification of ion wave dispersion is obtained when ion waves are excited externally. The frequency shift and suppression of ion wave instabilities are observed. These phenomena are discussed under the new theoretical analysis.

Optical Measurement of a High-Frequency Electric Field in a Weakly Ionized Plasma

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Longitudinal Wave Propagation in a Plasma Containing an External Time-Dependent Electric Field

Frequency and damping decrements for high frequency longitudinal oscillations in a plasma containing an external high frequency (Ω ≫ k υ¯_) electric field are obtained by means of a time-asymptotic solution to the linearized Vlasov equation, with an approximate collision term included. If the external field frequency is close to (ωp_2 + 3 k2υ¯_2)1/2, the contribution of the ion motion to Landau damping is significant for small external fields. The threshold field necessary to excite a high frequency instability in a plasma in which the number of a particles in a Debye sphere is very large is obtained. This problem is of interest since laser-induced instabilities may be responsible for an anomalous heating effect in the plasma.

Differential thermal analysis using high frequency dielectric heating I. Theory and equipment

AbstractA new analytical technique, differential thermal analysis using high frequency dielectric heating (DTA/HF), has been developed which senses the rate and extent of the enthalpy change accompanying curing. These two parameters relate simply and quantitatively to curing reaction kinetics.In DTA/HF cylindrical samples of uncured elastomers, 2‐in. in diam and about 1‐in. high, enclosed in glass rings and covered, are heated in a high frequency (86 mc) electrical field simultaneously with an identically‐shaped precured reference disc of the same elastomer. Both sample and reference are clamped securely between 3 × 5‐in. rectangular output electrodes. The sample is cured isometrically under pressure generated by thermal expansion. Temperatures at the core of the sample and reference are monitored continuously using ungrounded junction thermocouples with stainless steel probes; both sample temperature and temperature differences between sample and reference are recorded.To test the validity of DTA/HF it was first applied to the dicumyl peroxide (DCP) curing of several cis‐1,4‐polyisoprene calcium carbonate mixtures for which reaction mechanisms and reaction kinetic data are available.

Influence of High-Frequency Electric Fields on Equilibrium and Stability of Toroidal Plasmas

The effect of a high-frequency toroidal electric field on equilibrium and stability of a toroidal plasma is considered. It is shown that for some values of the electric field, one can change the particle orbits considerably with important consequences to diffusion and stability.

Effects of a High-Frequency Electric Field on Micro-Instabilities Driven by Density Gradient

Drift, drift-dissipative, and drift-cyclotron instabilities in an inhomogeneous plasma are considered for the case when a uniform high-frequency electric field is applied along the magnetic field. For the applied field, the dipole approximation is made and the skin effect is neglected. Without averaging the distribution function over the period of the applied electric field, the dispersion relations are derived for both the collisionless and collisional regimes. It is found that the high-frequency field whose frequency is within some ranges increasing the frequencies of perturbations can stabilize drift instabilities and also drift-cyclotron instabilities with finite k z of the fluid-type, where k z is the component of the wave vector along the magnetic field. It is found, however, that when the unstable drift-dissipative mode is stabilized the stable mode becomes unstable.

Elektronenbeschleunigung in einem Plasmabetatron mit und ohne hohem Leitungsstrom

A previous paper by Drees and Paul reported measurements on a plasma betatron. The study was continued using a betatron field with a vector potential taking into account the self magnetic field of a plasma current. The plasma was produced by a high frequency electric quadrupole field without an azimuthal magnetic field. The bremsstrahlung intensity of the accelerated electrons was observed as a function of gas pressure and accelerating field. The maximum energy of the electrons was 1.3 MeV compared to 1.5 MeV given by the field parameters. The maximum number in this energy range was about 1010 per pulse corresponding to a circulating runaway current of ∼ 1 A. The conduction current was drasticly reduced by coating the inner wall of the quartz glass torus with a thin layer of graphite. This change in the plasma current did not influence the γ radiation intensity.

Electrostatic Plasma Instabilities Excited by a High-Frequency Electric Field

The electrostatic plasma waves excited by a uniform, alternating electric field of arbitrary intensity are studied on the basis of the Vlasov equation; their dispersion relation, which involves the determinant of either of two infinite matrices, is derived. For ω0 ≫ ωpi (ω0 being the applied frequency and ωpi the ion plasma frequency) the waves may be classified in two groups, each satisfying a simple condition; this allows writing the dispersion relation in closed form. Both groups coalesce (resonance) if (a) ω0 ≈ ωpe/r (r any integer) and (b) the wavenumber k is small. A nonoscillatory instability is found; its distinction from the DuBois-Goldman instability and its physical origin are discussed. Conditions for its excitation (in particular, upper limits to ω0,k, and k·vE, vE being the field-induced electron velocity), and simple equations for the growth rate are given off-resonance and at ω0 ≈ ωpi. The dependence of both threshold and maximum growth rate on various parameters is discussed, and the results are compared with those of Silin and Nishikawa. The threshold at ω0 ≈ ωpi/r,r ≠ 1, is studied.

Ion Correlations due to a High-Frequency Electric Field and Their Effect on the Nonlinear Plasma Conductivity

The influence of a strong, high‐frequency electric field on the ion‐ion correlations in a fully ionized plasma is investigated in the limit of infinite ion mass, starting with the Bogoliubov‐Born‐Green‐Kirkwood‐Yvon hierarchy of equations; a significant departure from the thermal correlations is found. It is shown that the above effect may substantially modify earlier results on the nonlinear high‐frequency plasma conductivity.

Enhancement of ionization in nitrogen by excited nitrogen molecules and their de-activation

The rate of ionization of nitrogen at 300 K and at gas pressures of 1 to 30 Torr is considerably increased by admixing neutral molecules of electronically excited nitrogen, N*2. This effect is demonstrated by measuring the corresponding decrease in electric strength as a function of the population of the excited species. These are produced in a weak electric discharge which is maintained at one end of a long tube filled with N2. From there they diffuse into the test region at the other end where a high frequency electric field is applied to determine electric breakdown voltage of the partially excited gas. Gas contamination is avoided by using external electrodes throughout. The population of N*2in the test region is varied by changing the gas pressure and the distance between the test region and the source whose activity is kept constant. It is found that at a pressure of about 1 Torr and a distance of 10 cm the electric strength of N2+ N*2is up to 15% smaller than that of N2. The presence of N*2is also detected by the colour change of a metal oxide powder with which it reacts; for example, pale green MoO3exposed to N*2is reduced to blue MoO2within 10 to 100s. From the time interval between the exposure of the powder to the gas and the colour change, the relative concentration of N*2is obtained as a function of distance in a 4 cm wide tube up to 80 cm from the source at pressures up to 30 Torr when the system is kept in a steady state. In addition, the time dependence of the concentration along the tube is observed in the non-steady state. A colour test with calcium shows that outside the source nitrogen atoms are negligible in numbers. Also by means of a platinum resistance wire the total energy flux and the number of N*2is measured and, with an electron emission detector, their spatial distribution is again confirmed. Analysis of the results shows that the extremely slow decay of N*2at lower pressures is essentially controlled by spontaneous radiation and wall collisons, whereas collision deactivation sets in above about 10 Torr. It is concluded that the bulk of N*2outside the source is in the A(3∑u+) state with a free life of 12 s and a concentration of about 1013particles/cm3at 1 Torr; hence 1 part in 104of N2are electronically excited. The efficiency of wall deactivation to the ground state of N2by Pyrex glass and platinum is found to be 3 × 10-5and 3 × 10-3respectively, the efficiency of electron emission from platinum is about 10-7excited molecules per electron collected and the upper bound of the activation energy for reducing MoO3is 6.1 eV, the zero vibrational level of the A state. Since the potential energy of two A state molecules is smaller than the ionization energy of N2, deactivation by ionization along the tube is not feasible. However, enhancement of ionization can occur in an electric field when electrons collide with such long-lived excited molecules thus raising them to higher vibrational levels so that pairs with a potential energy ≥ ionization energy can produce ionization on collision.

Anomalous Friction Due to Microturbulence

The effects of a stochastic electric field of high frequency and phase velocity on the dynamics of a low-velocity particle is studied. It has been shown that the effect of such fields, to second order in the electric field strength, is to introduce an anisotropic drag force into the equations of the particle dynamics which, as in the collisional case, is linearly related to the particle velocity and vanishes when the autocorrelation time of the statistical electric field vanishes.

Frequency Limit of LSA-Mode Oscillations Estimated from the Hot Electron Problems in the High Frequency Electric Field

The frequency dependence of the drift velocity-field characteristics of n-type GaAs and the frequency limit of LSA-mode oscillations were investigated by solving the time dependent conservation equations of the electron number, momentum and energy for the lower and upper valleys. The velocity-field characteristics at high frequencies differed significantly from that for DC field and showed hysteresis loops. The maximum frequency of the LSA mode oscillation was estimated to be about 150 GHz.

Spectroscopic Measurement of High-Frequency Electric Fields in a Plasma by Observation of Two-Quantum Transitions and Spectral Line Shifts

We have observed normally forbidden two-quantum transitions in the optical spectrum of a helium plasma. We induced these transitions by applying a microwave field to a separately generated steady-state helium discharge. Measurements of the relative intensity and wave-length of the optical photons emitted in the two-quantum transition $5^{1}F^{0}\ensuremath{\rightarrow}2^{1}P^{0}$ in He I determined both the frequency and the strength of the microwave field in the plasma. The field strength was also measured by observation of the Stark shift of a spectral line and by measurement of the microwave power input and the $Q$ of the microwave cavity. All measurements of the field strength are in satisfactory agreement and indicate an rms microwave field strength in the plasma of about 215 V/cm. The spectroscopic measurement of the frequency of the microwave field is within 3% of the actual value, and the measured polarization of the radiation agrees with theory.

Stabilization of Drift Cyclotron Instabilities by a High-Frequency Electric Field

Stabilization of Drift Cyclotron Instabilities by a High-Frequency Electric Field