Showing papers on "Drift velocity published in 1994"

Molecular dynamics simulation of ionic mobility. i: alkali metal cations in water at 25 c

Abstract: We describe a series of molecular dynamics simulations performed on model cation‐water systems at 25 °C representing the behavior of Li+, Na+, K+, Rb+, and Cs+ in an electric field of 1.0 V/nm and in its absence. The TIP4P model was used for water and TIPS potentials were adapted for the ion‐water interactions. The structure of the surrounding water molecules around the cations was found to be independent of the applied electric field. Some of the dynamic properties, such as the velocity and force autocorrelation functions of the cations, are also field independent. However, the mean‐square displacements of the cations, their average drift velocities, and the distances traveled by them are field dependent. The mobilities of the cations calculated directly from the drift velocity or the distance traveled by the ion are in good agreement with each other and they are in satisfactory agreement with the mobilities determined from the mean‐square displacement and the velocity autocorrelation function in the absence of the field. They also show the same trends with ionic radii that are observed experimentally; the magnitudes are, however, smaller than the experimental values in real water by almost a factor of 2. It is found that the water molecules in the first solvation shell around the small Li+ ion are stuck to the ion and move with it as an entity for about 190 ps, while the water molecules around the Na+ ion remain for 35 ps, and those around the large cations stay for 8–11 ps before significant exchange with the surroundings occurs. The picture emerging from this analysis is that of a solvated cation whose mobility is determined by its size as well as the static and dynamic properties of its solvation sheath and the surrounding water. The classical solventberg model describes the mobility of Li+ ions in water adequately but not those of the other ions.

Large amplitude electric and magnetic field signatures in the inner magnetosphere during injection of 15 MeV electron drift echoes

Abstract: Electric and magnetic fields were measured by the CRRES spacecraft at an L-value of 22 to 26 near 0300 magnetic local time during a strong storm sudden commencement (SSC) on March 24, 1991 The electric field signature at the spacecraft at the time of the SSC was characterized by a large amplitude oscillation (80 mV/m peak to peak) with a period corresponding to the 150 second drift echo period of the simultaneously observed 15 MeV electrons Considerations of previous statistical studies of the magnitude of SSC electric and magnetic fields versus local time and analysis of the energization and cross-L transport of the particles imply the existence of 200 to 300 mV/m electric fields over much of the dayside magnetosphere These observations also suggest that the 15 MeV drift echo electrons were selectively energized because their gradient drift velocity allowed them to reside in the region of strong electric fields for the duration of the accelerating phase of the electric field 10 refs, 3 figs

Velocity distribution functions and transport coefficients of atomic ions in atomic gases by a Gram—Charlier approach

Abstract: A new model, based on a Gram—Charlier series, is presented for the ion velocity distribution function of atomic ions moving in atomic gases under the influence of an electric field. The model involves eight parameters: the ion drift velocity, longitudinal temperature, transverse temperature, coefficient of skewness along the field, kurtosis along the field, kurtosis perpendicular to the field, coefficient of correlation between parallel velocity and perpendicular energy, and coefficient of correlation between parallel and perpendicular energy. The model is used as the foundation for solving the Boltzmann kinetic equation by a method of weighted residuals. Applications are made to a variety of ion—neutral systems to illustrate the usefulness of the model.

Performance of a three-ton liquid argon time projection chamber

Abstract: We have constructed and operated a 3 ton liquid argon time projection chamber as part of the R&D programme for the ICARUS project. We report on the analysis of events from cosmic rays and from radioactive sources collected from June 1991 to June 1993. We have systematically investigated the performance and the physical parameters of the detector. We present here the results obtained from the analysis of the cosmic rays data on the following items: the electron drift velocity, the electron lifetime, the free electron yield, the electron diffusion coefficient, the space resolution and the particle identification capability. The data from radioactive sources are used to study the energy resolution in the MeV range. The in depth understanding of the basic physics aspects of the liquid argon TPC allows us to conclude that such a detector can be built in large sizes and reliably operated over long periods of the time, providing a new instrument for physics experiments.

Scanning tunneling microscope calibration and reconstruction of real image: Drift and slope elimination

Abstract: Drift, slope of sample, and indeterminate sensitivity of piezoceramics are considered as the origin of the linear scanning tunneling microscope (STM) image distortions. A special algorithm of STM scanning and reconstruction of image of unknown atomic structures is suggested and tested. This algorithm allows us to measure three components of the drift velocity and two angles, characterizing the average slope of scanning surface. On the one hand, using this algorithm, one can perform the STM calibration by a known surface structure (for example, the highly oriented pyrolytic graphite surface) even in the presence of a drift. This enables us to determine all the three piezoceramics constants of STM piezoscanner and the deviation of the real scanner axes X and Y from orthogonality. On the other hand, using such a calibrated STM and the described algorithm, it is possible to obtain the real STM image and make measurements for unknown surfaces with atomic resolution without the distortions mentioned above. As i...

A formula for ‘wave damping’ in the drift of a floating body

Abstract: A simple formula for ‘wave damping’ is derived, exact within the context of the proposed theory, namely: potential flow correct to second order in the wave amplitude and to leading order in U/c, where U is the drift velocity and c the wave celerity. The analysis is restricted to a two-dimensional problem although the extension to three dimensions seems possible.

Ion drag and plasma-induced thermophoresis on particles in radiofrequency glow discharges

Abstract: A comparison is made of the forces governing the transport of negatively charged particles electrostatically suspended in the plasma of a symmetric parallel-plate radiofrequency glow discharge with isothermal walls. The two forces driving the particles symmetrically from the plasma centreline to the sheath edges are the ion drag force and the plasma-induced thermophoresis due to the thermal gradient appearing in the gas heated by plasma power dissipation. A general expression of the ion drag force as a function of the ratio of the ion drift velocity and thermal velocity is obtained by a proper integration over the ion energy distribution using the analytical expression for the ion orbital momentum transfer cross section derived by Kilgore et al. (J. Appl. Phys. 73 7195 (1993)). The ion drag force is then compared with the plasma-induced thermophoresis on submicrometre-size particles in well-characterized experimental discharge conditions in Ar. It appears that ion drag is usually larger than thermophoresis on an isolated particle in a pristine discharge. However, thermophoresis always dominates over ion drag in dusty discharges where plasma-particle and particle-particle interactions result in a drastic reduction of the ion drift velocity through the plasma bulk.

Multiple light scattering in Taylor-Couette flow

Abstract: We report dynamic light scattering experiments on turbid colloidal suspension under stationary and laminar flow, as well as in the regime of flow instabilities. It is shown that the time autocorrelation function C 1 ( t ) = E (0) E ∗ ( t )>/ E (0)¦ 2 > of the scattered light field E ( t ) is not sensitive to the mean velocity flow but rather to the root mean square of velocity gradient. C 1 ( t ) is characterised on the level of each scattering event by the correlation time required by a pair of scatterers initially separated by a transport mean free path to move a relative distance of optical wavelength due to the velocity gradient. We verified this theoretical analysis using planar Couette flow as an example for homogenous velocity gradients, and planar Poiseuille flow for inhomogeneous velocity gradients. Agreement between expirement and theory is excellent. Finally, this technique is applied to spatially varying velocity gradient fields for measuring the threshold and wave number of the Taylor-Coutte instability. This illustrates the possibility of studying hydrodynamic instabilities and quasi-local velocity gradients even under conditions of strong multiple scattering.

Measurement of the velocity of current filaments in optically triggered, high gain GaAs switches

Abstract: Pictures are presented of the time evolution of current filaments during optically triggered, high gain switching in GaAs. Two filaments are triggered with two laser diode arrays and the time delay between them is varied. When the filament that is triggered first crosses the switch the voltage drops and the other filament ceases to grow. By varying the delay between the lasers, the tip velocity is measured to be 2±1×109 cm/s, 100 times larger than the peak drift velocity of carriers in GaAs. This observation supports switching models that rely on carrier generation at the tip of the filament.

Nonuniform muscle fiber orientation causes spiral wave drift in a finite element model of cardiac action potential propagation.

Abstract: Mechanism for Spiral Wave Drift. Introduction: Reentrant tachyarrhythmias are thought to involve spiral waves of excitation and recovery that may be nonstationary. The effect of muscle fiber curvature on spiral and planar wave propagation was studied using a computational model. Methods and Results: Two-dimensional anisotropic cardiac propagation was modeled using a finite element method to solve a modification of the FitzHugh-Nagumo equations. Spiral waves that propagated stably about a fixed core in tissue with a uniform fiber orientation were found to drift at an oblique angle to the fibers when the fibers curved. The drift velocity was linearly related to the fiber angle gradient and was 10% of the longitudinal propagation velocity with a gradient of 4 degree/cm. Planar wavefronts were also affected by fiber curvature. The maximal upstroke rate, propagation velocity, and the action potential amplitude all increased when the fibers curved toward the wavefront and decreased when they curved away. For example, when the fibers curved toward the wavefront with a moderate gradient of 15 degree/cm, maximal upstroke rate increased 74%, transverse propagation velocity increased 65%, and action potential amplitude increased 9%, This phenomenon caused the spiral wave drift: As a spiral wave traverses a cycle, the angle between the wavefront at the wavetip and the fibers changes periodically, thus altering the propagation parameters. These periodic changes affect the instantaneous radius of curvature of the wavetip path, which results in drift. Conclusion: Spiral and planar waves are affected by muscle fiber curvature. The resulting dynamics may be important in determining the lifetime and stability of reentrant arrhythmias.

Ion acoustic solitons in a plasma with finite temperature drifting ions: Limit on ion drift velocity

Abstract: Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity u0 for which the ion acoustic solitons are possible, is obtained. The solitons can exist for vTe≤u0≤‖u0 max‖, where vTe is the electron thermal velocity and u0 max is the maximum value of the ion drift velocity. The maximum value of this velocity is decided by the ion temperature. Under the limiting conditions, the Korteweg–deVries (KdV) equation is derived for one‐dimensional ion acoustic soliton. Expressions are obtained for the soliton phase velocity, peak soliton amplitude, soliton width, and the soliton energy. The present results correspond to those of the previous investigations under appropriate plasma conditions.

Measurement of ion flows using an ‘‘unmagnetized’’ Mach probe in the interchangeable module stellarator

Abstract: A Mach probe is used to measure poloidal and toroidal flows induced by a biased electrode in IMS. Mach probe theories are reviewed and classified as either magnetized or unmagnetized. A simple geometric model of the IMS Mach probe shows that the variation of the effective probe area as a function of the probe orientation with respect to the magnetic field is 20%–25%, predicting the probe to be only slightly magnetized. Measurements of the variation in the total ion saturation current collected by the probe, as the angle with respect to the magnetic field is varied, demonstrate this level of magnetization only at low neutral pressure at large minor radius, while in other cases the variation in the total collected current is negligible. Based on this result an unmagnetized model [M. Hudis and L. M. Lidsky, J. Appl. Phys. 41, 5011 (1970)] is chosen to analyze the IMS Mach probe data. Comparison of Mach probe poloidal flow measurements as a function of minor radius to calculations of the E×B drift velocity an...

Simulation of Ion Trajectories near Submicron-Patterned Surface Including Effects of Local Charging and Ion Drift Velocity toward Wafer

Abstract: Ion trajectories near a submicron-patterned surface were investigated using numerical simulations including the effects of local charging on the patterned surface and ion drift velocity toward the wafer. The simulation results were also discussed relative to the etched profile characteristics in electron cyclotron resonance (ECR) plasmas with a divergent magnetic field. Since the pattern size was much smaller than the Debye length, charge neutrality was not satisfied on the submicron-patterned surface. The simulated ion trajectories were largely deflected at the inside of the outermost lines of line-and-space patterns. Moreover, the ion trajectory deflection was reduced with increasing ion drift velocity. These simulation results showed a similar tendency as the etching characteristics.

Time-resolved optical second harmonic generation measurements of picosecond band flattening processes at single crystal TiO2 electrodes

Abstract: Time-resolved optical second harmonic generation (SHG) is used to probe the variations in the surface electrostatic fields that occur under pulsed UV (supra-bandgap) illumination at a n-TiOZ(001) electrode. The interfacial SHG is dominated by the electric field-induced second harmonic response from the first 20 nm of the semiconductor surface; this large SHG signal decreases sharply under UV illumination due to the creation of a steady-state photogenerated hole population at the interface. An additional transient drop in SHG intensity is observed when the pump and probe beams are overlapped temporally on the Ti02 surface. The time scale for this additional band flattening is determined by the finite time required for photogenerated holes to migrate to the interface under the influence of the surface electrostatic fields. An average transit time of 25 ps that is independent of applied potential or solution composition is observed; this corresponds to a hole drift velocity of 4.0 x 104 cm s-' at the Ti02 surface. The SHG intensity is found to return to its steady-state level in 3-4 ns due to the removal of the excess holes at the surface by electrochemical charge transfer and surface recombination processes.

Parametric resonance of a vortex in an active medium.

Abstract: Experimental observation of parametric resonance of a vortex in an active medium is reported. Unlike the parametric resonance in conservative systems, no parametric pumping of energy is involved here, making the resonance especially interesting. An alternating electric-field with frequency, equal to double frequency of the vortex rotation, has induced the vortex drift in the Belousov-Zhabotinsky chemical active medium. The drift velocity was about 1/5 of the vortex drift velocity in constant electric field with the same amplitude. The direction of the drift did not coincide with the direction of the electric field and could be arbitrarily chosen by changing the phase shift between the electric-field oscillations and the vortex rotation. No effects were observed at a frequency equal to the frequency of vortex rotation, as well as at nonresonant frequencies.

Response of a Bloch oscillator to a THz-field

Abstract: In this paper we report on the observation of response of a Bloch oscillator at room temperature to a THz-field of a frequency larger than the Bloch frequency. The oscillator consisted of a semiconductor superlattice structure, with an applied dc voltage giving rise to a dc electron drift current. Submitting the oscillator to a field at a frequency of 3.3 THz caused a sizeable reduction of the current; the THz-field was generated by use of intense THz-radiation pulses focused on an antenna coupled to the superlattice. We attribute the THz-field induced reduction of the current to a frequency modulation of the Bloch oscillations of electrons at the frequency of the THz-field, leading to reduction of the electron drift velocity and, consequently, of the current.

Simple formulation of magnetoplasmadynamic acceleration

Abstract: A simple formulation of magnetoplasmadynamic acceleration has been made based on energy conservation relations and a generalized Ohm’s law. An exhaust velocity is expressed using three characteristic parameters: (1) a dimensionless characteristic velocity U≡μ0J2D/(muA) (JD is the discharge current, m is the mass flow rate of working fluid, uA is the Alfven’s critical velocity, and μ0 is the permeability in vacuum); (2) the ratio of an applied to self‐induced magnetic fields; and (3) an electron Hall parameter. An exhaust velocity calculated using the formula agrees well with the experimentally measured value.

A simple theory of conditional mean velocity in turbulent scalar‐mixing layer

Abstract: This paper presents the experimental results on conditional mean transverse velocity across a turbulent scalar mixing layer. The velocity is conditioned on mixture fraction. It is found that the distribution of the conditional mean transverse velocity is closely related to the local mean‐mixture fraction in physical space. Near the local mean‐mixture fraction a linear relationship exists between the conditional mean transverse velocity and the mixture‐fraction fluctuations. Departure from the linear relationship at large mixture‐fraction fluctuations is mainly due to the nonlinear distribution of the mean mixture‐fraction profile and it is not, as has been suggested by others, due to the limiting velocity of the large eddies in the flow.

Elastic excitable medium.

Abstract: A type of excitable medium---an elastic excitable medium---has been created by incorporating the Belousov-Zhabotinsky reaction into a polyacrylamide-silica gel. It permits one to address the problem of how the cardiac muscle contractions affect the dynamics of rotating spiral waves. Investigations of the effects of mechanical deformations on the excitation wave propagation exhibit a resonance dynamics of vortices. For equal frequencies of deformation and of vortex rotation, vortices drift. The drift velocity is about 3% of the excitation wave velocity, for a 50% elongation. The direction of the drift does not coincide with the stretching direction and can be varied by changing the phase shift between deformations and vortex rotation. Numerical calculations suggest that the effects of mechanical deformations on excitation wave propagation are independent of the exact nature of the excitable medium.

Acceleration and heating of cold ion beams in the plasma sheet boundary layer observed with GEOTAIL

Abstract: The GEOTAIL/Low Energy Particle (LEP) observations have revealed detailed features of acceleration and heating of cold ion beams in the plasma sheet boundary layer (PSBL). In the lobe region, the cold ion beams are flowing tailward nearly along magnetic field lines with small perpendicular drift toward the plasma sheet. Upon entering the plasma sheet, these cold ion beams are heated and accelerated up to several keV/q in the PSBL where a high-speed ion flow is observed separately and simultaneously, and finally assimilated into the hot component of the plasma sheet proper. It should be noted that the acceleration of the cold ion beams in the PSBL is observed in the direction perpendicular to the magnetic field, and the perpendicular velocities of the cold ion beams during the acceleration coincide well with those of the high-speed ion beams. This fact suggests that the perpendicular acceleration is due to an increase of the E×B drift speed in the PSBL as particles move from the lobe to the central plasma sheet. The electric field intensity for the observed E×B drift motion is estimated as 2–5 mV/m. The direction of the electric field inferred from the ion motion in the PSBL is mainly in the south-to-north direction rather than the dawn-to-dusk direction which is generally thought to be typical in the tail lobe. The direction of the acceleration is at times observed to change drastically, which suggests that the electric field direction fluctuates significantly as well.

Ion acoustic solitons in finite ion temperature inhomogeneous plasmas having negative ions

Abstract: Analytical investigations are carried out for ion acoustic soliton propagation in a spatially inhomogeneous plasma having finite temperature negative and positive ions. The soliton characteristics are described by a Korteweg–de Vries equation which has additional terms. Rarefactive solitons are possible in the negative ion containing plasma, and their existence is decided by the nonlinearity coefficient of this equation. The soliton amplitude decreases for higher‐density gradients, but it increases with the increasing ratio of negative‐to‐positive ion density. Effect of temperature and drift velocity, of both the positive and negative ions on soliton propagation, has been analyzed.

The effect of wave‐particle interactions on the polar wind O+

Abstract: The escape of the polar wind plasma is an important element in the ionosphere-magnetosphere coupling. Both theory and observations indicate that the wave-particle interactions (WPI) play a significant role in the dynamics of ion outflow along open geomagnetic field lines. A Monte Carlo simulation was developed in order to include the effect of the WPI in addition to the factors that are traditionally included in the 'classical' polar wind (i.e. gravity, electrostatic field, and divergence of geomagnetic field lines). The ion distribution function (f(sub j)), as well as the profiles of its moments (density, drift velocity, temperature, etc.) were found for different levels of WPI, that is, for different values of the normalized diffusion rate in the velocity space (D(tilde) (sub j perpendicular). Although the model included O(=), H(+) and eletrons, we presented only the results related to the O(+) ion. We found that (1) both the density and drift velocity of O(+) increased with the WPI strength, and consequently, the O(+) escape flux was enhanced by a factor of up to 10(exp 5), (2) The O(+) ions could be energized up to a few electron volts; (3) for moderate and high levels of WPI D(tilde) (sub perpendicular) (O(+) greater than (tilde) 1, the distribution function f(O(+)) displayed very pronounced conic features at altitudes around 3 R(sub e). Finally, the interplay between the downward body force, the upward mirror force, and the perpendicular heating resulted in the formation of the 'pressure cooker' effect. This phenomena explained some interesting features of our solution, such as, the peak in the O(=) temperature, and the formation of 'ears' and conics for f(O(+)) around 2.5 R(sub e).

Meridional drift in the large-scale solar magnetic field pattern

Abstract: A method of two-dimensional correlation functions has been applied to a sequence of synoptic maps of the large-scale magnetic field to obtain the meridional drift pattern of field structures. The meridional drift profile obtained is antisymmetric about the equator. The meridional drift is directed from the equator to the poles at latitudes below 45°. A maximum drift velocity of 11–13 m s−1 is attained in the latitude range 30°. A picture of the space-time distribution of meridional drift is also obtained, which may be interpreted as resulting from the effect of azimuthal convective rolls (3 rolls per hemisphere) on the large-scale magnetic field. Rolls originate at high latitudes following the cycle maximum, and migrate equatorwards until the minimum of the next cycle. The picture in the equatorial region can correspond to convective rolls with lifetimes of about two years, or to the process of interaction of rolls from two hemispheres.

The electrodynamics of a drifting auroral arc

Abstract: Simultaneous observations by EISCAT and the Kilpisjarvi all-sky camera revealed the presence of a band of enhanced electric field on one side only of an auroral arc. Both the arc and the enhanced electric field drifted equatorward at a velocity close to the prevailing convection velocity. The same drift speed was indicated by EISCAT measurements of ion-frictional heating: this descended in height as the magnetic field lines carrying the enhanced electric field cut across the EISCAT beam

A segmented disk electrode to produce and control parallel and transverse particle drifts in a cylindrical plasma

Abstract: A segmented disk electrode is described that produces and controls both relative drift parallel to the magnetic field and localized flow perpendicular to the magnetic field in a Q machine plasma. Measurements of the electron drift velocity vd with respect to the ions, and the electric field E for many bias‐voltage combinations are used to demonstrate the controllability of the ratio vE/vd, where vE=E×B/B2, in a narrow channel between the regions that magnetically map to the segments. Radial electric fields of magnitudes ranging from 0 to ±3 V/cm localized within a current channel with parallel electron drift velocities up to half the electron thermal velocity have been produced with the segmented disk electrode.

High-Field Electron Transport in SiGe Alloy

Abstract: Electron transport in unstrained Si1-x Gex (0≤x ≤0.4) alloy is studied in the present work using the Monte Carlo (MC) simulation technique. Electron transport characteristics (drift velocity, impact ionization (II) coefficient, etc.) are evaluated over a wide range of electric fields. It is found that not only low-field mobility but also saturation velocity and impact ionization coefficients are reduced with increasing Ge fraction due to alloy scattering. More importantly, the high-energy ( e>2 eV) electron population is reduced to a much greater extent than the ionization coefficient. Simple analytical expressions for electron low-field mobility, saturation velocity and II coefficient which can be easily implemented in device simulation programs are proposed.

Cross‐tail current, field‐aligned current, and By

Abstract: Orbits of individual charged particles were traced in a one-dimensional magnetic field model that included a uniform cross-tail component B(sub yo). The effects of B(sub yo) on the cross-tail current distribution j(sub y)(z), the average cross-tail drift velocity(nu(sub y)z), and the average pitch angle change(delta alpha) experienced during current sheet encounters were calculated. The addition of a B(sub yo) that exceeded several tenths of one nanotesla completely eliminated all resonance effects for odd-N orbits. An odd-N resonance involves ions that enter and exit the current sheet on the same side. Pitch angles of nearly all such ions changed substantially during a typical current sheet interaction, and there was no region of large cross-tail drift velocity in the presence of a modest B(sub yo). the addition of a very large B(sub yo) guide field in the direction that enhances the natural drift produces a large j(y) and small (Delta alpha) for ions with all energies. The addition of a modest B(sub yo) had less effect near even-N resonances. In this case, ions in a small energy range were found to undergo so little change in pitch angle that particles which originated in the ionosphere would pass through the current sheet and return to the conjugate ionosphere. Finally, the cross-tail drift of ions from regions dominated by stochastic orbits to regions dominated by either resonant or guiding center orbits was considered. The ion drift speed changed substantially during such transitions. The accompanying electrons obey the guiding center equations, so electron drift is more uniform. Any difference between gradients in the fluxes associated with electron and ion drifts requires the presence of a Birkeland current in order to maintain charge neutrality. This plasma sheet region therefore serves as a current generator. The analysis predicts that the resulting Birkeland current connects to the lowest altitude equatorial regions in which ions drift to or from a point at which stochastic orbits predominate. The proposed mechanism appears only in analyses that include non-guiding-center effects.

Lattice electromigration in narrow Al alloy thin-film conductors at low temperatures

Abstract: At low temperatures, electromigration in polycrystalline Al thin-film conductors has been considered to occur predominantly along grain boundaries. As conductor widths decrease below the average grain size, however, other transport mechanisms will become important. Here we examine electromigration transport mechanisms in narrow AlSiCu conductors in the temperature range 190 to 290°C using the stripe drift technique. For conductors with widths between 0.9 and 2.75 μm both the absolute values of the drift velocity and the activation energy for drift are consistent with a lattice diffusion mechanism. Over this linewidth range the Al microstructure ranges from near-bamboo to approximately 20 μm long polycrystalline segments. The independence of the drift data from the linewidth shows that steady state transport is controlled by the bamboo regions of the conductors, which results from the slower rate of diffusion of Al through the lattice compared to along grain boundaries.

The adverse effect of perpendicular ion drift flow on cylindrical triple probe electron temperature measurements

Abstract: The cylindrical triple probe method is an attractive technique for measuring electron temperatures (Te) and electron number densities (ne) in a variety of plasmas sources. In practice, however, the cylindrical triple probe can be sensitive to sources of error that affect all Langmuir probe techniques. In particular, the presence of an ion drift velocity component that is perpendicular to the probe axis has been known to result in erroneous measurements of ne. Less obvious, however, is that ion flow perpendicular to the probe has a significant effect on the indicated Te. The purpose of this note is to make researchers aware of such an effect and to demonstrate a technique which can mitigate it. The approach taken to investigate this phenomenon was to make Te measurements in the plume of a 20 kW magnetoplasmadynamic thruster with the probe oriented at several angles with respect to the local ion flow.

A study of electron drift velocity in ArCO2 and ArCO2CF4 gas mixtures

Abstract: We have measured the electron drift velocity as a function of electric field in ArCO 2 mixtures. Measurements are made for mixtures containing 8% to 20% CO 2 in 1% increments. Effects of air and nitrogen contamination on ArCO 2 mixtures are investigated. These results are useful for determining the correct mixing ratio of the ArCO 2 mixture in drift chamber applications. We have also measured the electron drift velocity in several ArCO 2 CF 4 mixtures.