Showing papers on "Diffusion current published in 1977"
TL;DR: In this article, the authors measured cross-field diffusion in the levitated octupole using two independent methods: direct measurements of the particle flux onto an internal ring surface and the shape of the density profile and the time decay of density at the separatrix.
Abstract: Measurements of cross‐field diffusion were made in the levitated octupole using two independent methods. First, the magnitude and scaling of D⊥ with density, n, and field strength, B, were determined by direct measurements of the particle flux onto an internal ring surface. Second, the shape of the density profile and the time decay of the density at the separatrix were compared with solutions of a diffusion equation model. Both methods indicated that D⊥ was proportional to n−1/2 and independent of B. The plasma was created by gun injection into the purely poloidal magnetic field and the initial parameters were ne∼5 ×109 cm−3, Ti∼20 eV, Te∼5 eV. The observed diffusion scaling can be understood within the framework of vortex diffusion in a high‐dielectric constant plasma if the spectrum of waves is enhanced in energy over thermal levels with an effective temperature, T*, of 104 eV.
40 citations
TL;DR: In this paper, the bounce-averaged drift kinetic equation with a model collision operator was studied in a tokamak field with ripples and it was shown that the banana drift diffusion is proportional to the collision frequency when the poloidal banana drift frequency is smaller than the effective collision frequency.
Abstract: The drift motions of trapped particles in a tokamak field with ripples lead to a new transport process in large tokamaks in addition to the diffusion process due to particles trapped in the ripples. This problem is studied by solving the bounce-averaged drift kinetic equation with a model collision operator. It is shown that the banana drift diffusion is proportional to the collision frequency when the poloidal banana drift frequency is smaller than the effective collision frequency. This result is contrary to earlier predictions. In a reactor regime, this loss mechanism is shown to be unimportant.
33 citations
TL;DR: In this article, the solution potential distributions in flow-through porous electrodes of fixed beds of spherical conducting particles are determined when the electrodes are working at the limiting diffusion current and they are shown to be in agreement with the corresponding theoretical distributions.
19 citations
TL;DR: In this article, the authors present an approach which permits the prediction of the limiting diffusion current of a polarographic reaction when the rotation speed of a disc electrode is sinusoidally modulated.
18 citations
TL;DR: In this article, thermal-limited diode performances were evaluated at 77°K in the whole 8-14 μm range and a theoretical model, mainly based on the Auger band-to-band process for carrier recombination, was assumed to explain such a behaviour for the one-sided abrupt junction.
16 citations
TL;DR: In this article, a general theory for the diffusion of a multi-ion species plasma across magnetic field due to electrostatic fluctuations is presented, and it is shown that the diffusion flux due to wave-particle interactions is not necessarily proportional to the density gradient of the particle species of interest.
Abstract: A general theory is presented for the diffusion of a multi-ion species plasma across magnetic field due to electrostatic fluctuations. It is shown that the diffusion flux due to wave-particle interactions is not necessarily proportional to the density gradient of the particle species of interest. The result is applied to the impurity diffusion due to those drift waves which exist in a single ion-species plasma. The dominant nonlinear effect is the induced scattering of waves on ions and the resulting diffusion constant of the host ions is given by the Kadomtsev formula, D ∼γ 2 / k 2 ω, where γ, ω and k are respectively the growth rate, frequency and wavenumber of the drift wave. The impurity diffusion constant is positive (or negative) if the impurity Larmour radius is smaller (or greater) than the host-ion Larmour radius, and becomes greater than the host diffusion constant if the spectrum is localized to the unstable region.
14 citations
TL;DR: In this article, drift wave induced cross field plasma transport is observed to destabilize new drift instabilities which then act to quench the original linear mode and enhance diffusion, which can then be used to enhance diffusion.
Abstract: Drift wave induced cross field plasma transport is observed to destabilize new drift instabilities which then act to quench the original linear mode and enhance diffusion.
10 citations
TL;DR: In this paper, electrical and optical measurements have been carried out at 300 K to ascertain the effects of neutron irradiation on the properties of red-emitting GaP:Zn,O light emitting diodes.
Abstract: Electrical and optical measurements have been carried out at 300 K to ascertain the effects of neutron irradiation on the properties of red‐emitting GaP : Zn,O light‐emitting diodes. Capacitance measurements at 300 K indicate that majority‐carrier removal is insignificant below a neutron fluence Φ of 1015 n/cm2. Above this value, a removal rate of 6.5 cm−1 is found. Current‐voltage data show that the total current increases with Φ at constant voltage and that the neutron‐added current is due to space‐charge recombination. The rate of increase in current with Φ leads to a lifetime–damage‐constant product τK of (3.0±0.9) ×10−14 cm2. A similar analysis of the degradation of the light output, which is due to a diffusion current at 300 K, results in τK= (2.4±0.4) ×10−14 cm2. This analysis also reveals that near the junction in the p region the concentration of Zn‐O pairs is linearly graded as is the Zn profile according to the capacitance data. Curves of efficiency versus current measured at 300 K possess maxi...
9 citations
TL;DR: In this paper, the currentvoltage characteristics of an enhancement-type insulated gate field effect transistor (E-type IGFET) are analyzed based on a one-dimensional model, taking account also of the diffusion current component.
Abstract: Current-voltage characteristics of an enhancement-type insulated gate field-effect transistor (E-type IGFET) are analyzed based on a one-dimensional model, taking account also of the diffusion current component. Explicit formulae for the entire I-V characteristic curve are given. The solution for the triode characteristic shows considerable deviation from “drift current theory” in terms of turn-on voltage (or threshold voltage) and drain voltage at just saturation. The solution for the pentode characteristic taking account of carrier's saturation velocity, shows that the increase in drain current per unit drain voltage is larger in short-channel devices than in long-channel devices. Agreement with experiment is very good.
8 citations
TL;DR: In this paper, a new liquid phase epitaxial growth system was developed for mass production of GaP green LED's having a high efficiency, which achieved an average external efficiency of 0.15 percent at a current density of 12.5 A/cm2 for unencapsulated uncontacted mesa diodes.
Abstract: A new liquid phase epitaxial growth system has been developed for mass production of GaP green LED's having a high efficiency. In this system, the n- and p-type layers are grown successively by the different melts on the n-type substrate. GaP substrates are set vertically in a horizontal array in an LPE boat. The main features of this system are that a high external efficiency is attained with an excellent reproducibility, that a large quantity of the substrates can be treated in one run, and that the quality of the growth layers is uniform in one wafer and among the wafers in one run. More than 100 runs have been carried out and the average external efficiency of 0.15 percent is obtained routinely at a current density of 12.5 A/cm2for unencapsulated uncontacted mesa diodes and the maximum external efficiency is 0.230 percent at 12.5 A/cm2. The high external efficiency may be caused by the high injection efficiency of the hole diffusion current.
6 citations
TL;DR: In this paper, the drain current of a triodelike JFET exhibits both positive and negative temperature dependence, depending on the current density, and the thermionic-injection mechanism prevails, leading to the positive temperature coefficient.
Abstract: The drain current of a triodelike JFET exhibits both positive and negative temperature dependence, depending on the current density. For drain current smaller than ∼5 A.cm-2, the thermionic-injection mechanism prevails, leading to the positive temperature coefficient. On the other hand, a space-charge-limited current flows in the case of current density larger than ∼10 A.cm-2, resulting in nearly T-1dependence due to the mobility decrease.
TL;DR: In this article, general equations for treating the diffusion of a magnetic field in a fluid with electrical conductivity and a resistive diffusion coefficient are given for the case of weak fluctuations in gas or field pressure, and the properties of a nonlinear diffusion equation are illustrated with the example of an initial thin slab of gas confined by a uniform field on either side.
Abstract: General equations are given for treating the diffusion of a magnetic field in a fluid with electrical conductivity and a resistive diffusion coefficient. Consequences of nonnegligible gas motion are investigated by considering the one-dimensional problem where a tenuous isothermal gas with pressure expressed as a function of x-coordinate and time is enmeshed in a magnetic field in the y-direction. Approximate equations are obtained for the case of weak fluctuations in gas or field pressure, and the properties of a nonlinear diffusion equation are illustrated with the example of an initial thin slab of gas confined by a uniform field on either side. The advance of a gas front into a nonvanishing gas density is illustrated by using the progressive wave solution. Application of the results to the evolution of streamers and filaments observed in the solar corona is briefly discussed
TL;DR: In this paper, two models of intervalley scattering are considered: in one model, coupling with hightemperature intervalley phonons only is assumed; in the other, low-temperature intervals are also included.
TL;DR: In this paper, an arbitrarily moving medium, e.g., a plasma, under the influence of an electromagnetic and gravitational field is considered, and the expressions for the electric current density and the diffusion current density are calculated.
Abstract: An arbitrarily moving medium, e.g. plasma, under the influence of an electromagnetic and gravitational field is considered. After solving the equation of motion for the charged particles by using a special approximation technique the expressions for the electric current density and the diffusion current density are calculated. By this procedure explicit formulae for the atomistic material coefficients are found. Of particular interest is the generation of an electric current, i.e. also a magnetic field, by the Poynting vector. The corresponding material coefficients show a characteristic frequency dependence. Numerical estimates exhibit an interesting order of magnitude of the expected effects.
TL;DR: In this paper, it was shown that the onset of concentration polarization by itself does not eliminate the nonuniformity of the potential distribution along the mercury drop surface, and the implications of this result for the theory of polarographic maxima of the 1st kind are considered.
TL;DR: In this article, a steady-state neoclassical diffusion calculation for conditions appropriate to tokamaks is described, where particle loss by diffusion is balanced by neutral recycling, and it is found that with the boundary condition that the particles convect out their own energy, the electron temperature and current density are large at the boundary.
Abstract: Steady-state neoclassical diffusion calculations are described for conditions appropriate to tokamaks. Particle loss by diffusion is balanced by neutral recycling. It is found that with the boundary condition that the particles convect out their own energy, the electron temperature and current density are large at the boundary. The means by which the behaviour of the temperature at the boundary may be brought closer to that observed in experiments are discussed.
TL;DR: In this article, the authors proposed to add a diffusion region adjacent to the injection plane of the BARITT structure to remove the zero-velocity singularity in the conventional analysis and account for an appreciable delay.
Abstract: Carriers are injected into the delay path of the BARITT structure with zero drift velocity, hence, diffusion can not be neglected in the small signal analysis. The inclusion of a diffusion region adjacent to the injection plane produces a more physically reasonable approach to the small signal analysis. This analysis is accomplished through a regional approximation. The three regions are the diffusion region (where diffusion dominates the conduction process) a low field region (where drift dominates but the carrier velocity has not reached the saturation velocity) and a high field region (where the carriers drift with a saturated velocity). The inclusion of the diffusion region removes the zero-velocity singularity which results in the conventional analysis and accounts for an appreciable delay which has been previously neglected. The device characteristics are optimized for various device parameters. The optimized device length and most probable value of the negative resistance are given, and a qualitative discussion of the physical origin of the behavior of the device characteristics is given.