Homogeneous Electrostatic Field Research Articles

Fringing-field effects in acceleration columns

Abstract Fringing-field effects in acceleration columns are investigated, based on the fringing-field integral method. Transfer matrices at the effective boundaries of the acceleration column are obtained, as well as the general transfer matrix of the region separating two homogeneous electrostatic fields with different field strengths. The accuracy of the fringing-field integral method is investigated.

Concerning the Electrical Interaction of Circular Holes in a Plane Conducting Screen

The potential problem of two nearby holes in an infinitely thin perfectly conducting screen immersed in a homogeneous normal electrostatic field is considered. Expressions are derived for the double layer of charge arising in the plane of the hole, the centre of gravity of this distribution and the total amount of polarization induced by a nearby point dipole. In the derivation a set of integrals are used that connect the terms of a series expansion of the potential in the oblate spheroidal system of co-ordinates with sources on the focal disk. The results are applied to solve the excess polarization and centre of the dipole distributions for two similar as well as two dissimilar holes.

Analyses of Spatially Resolved Electron Energy Distribution and Transport Properties in Steady State in CF4

Under homogeneous electrostatic field in gas between two plane electrodes, the electron energy distribution and transport properties near the electrodes are usually position dependent. Boltzmann equation analyses for such position dependent energy distribution and transport properties in steady state are very few due to its difficulty. In this paper, position dependent electron behaviors in CF 4 calculated using the Steady State Townsend flight time integral method (SST-FTI) for several boundary conditions are presented with the theory of the SST-FTI.

NLSDA calculations for H 3 on Rh 5 including high electric fields: Could linear H 3 be stable on Rh-tips?

We present ab initio calculations in non-local spin density approximation for up-right standing linear H 3 on a Rh 5 pyramid, which simulates a kink site and its nearest neighbours of a (100) oriented Rh-tip, including external homogeneous electrostatic fields. In these calculations all distances between the hydrogen nuclei as well as the distance between linear H 3 and the top-most Rh atom have been varied. For zero field linear H 3 is found to be unstable on Rh 5 in agreement with experiments. For fields between 2 and 3 V/Å linear H 3 is predicted to be stable. The energy barrier for H 3 dissociating from Rh 5 decreases gradually with increasing field until it vanishes at 3 V/Å. These theoretical predictions disagree with experimental results. The possibility of triangular H 3 is addressed.

Molecular dynamics simulation of gaseous ion-motion in electrostatic fields

A molecular dynamics (MD) method has been developed for the simulation of the motion of ions in neutral gases under the influence of homogeneous electrostatic fields. The method treats the translational motion of the ions and gas molecules classically and thus requires as input the ion–molecule interaction potentials. The continuous dissipation of a part of the ion-energy to a thermal bath is accomplished through the introduction of ‘‘iconical interactions’’ between ions and images of the neutrals created and stored in the memory of a computer during ion–atom encounters. The steady ion motion is then simulated by usual equilibrium MD methods using periodic boundary conditions. The resulting ion mobilities, effective temperatures, and third other velocity-distribution moments, expressed as skewness parameters, compare well with available results derived from the moment solution of Boltzmann equation and Monte Carlo simulations using the same interaction potentials in the cases of K+ in He and Ar, as well as of Ba+ in Ar. The additional reproduction of experimental data provides an independent test for the accuracy of the employed model potentials. Although the method has been applied to atomic systems it is easily extendable to the more complex molecular systems but at the expense of computer time.

High-field transport in semiconductors. I. Absence of the intra-collisional-field effect.

We show that the Levinson (Zh. Eksp. Teor. Fiz. 57, 660 (1969) [Sov. Phys.---JETP 30, 362 (1970)]) quantum transport equation reduces to the semiclassical Boltzmann equation in the limit of a strong homogeneous electrostatic field. To arrive at this conclusion we use a saddle-point approximation which has not been used in this field before. This approximation is exact in the high-field limit. We show that even for a relatively moderate field strength of 3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ V/m in GaAs (even before the onset of the Gunn effect, when 90% of the electrons are still in the central valley) the saddle-point approximation can be used for a majority of the scattering events. The results in this paper are supported by numerical calculations based on realistic scattering mechanisms in GaAs.

Orientation in molecule surface dynamics

Using an electrostatic hexapole focusing technique a state selected NO [2Π1/2(J=1/2, Ω=1/2, MJ=1/2)] beam is produced. This selected state has a preferential orientation of the internuclear axis with respect to an electrostatic field. By scattering this beam from a crystal placed in a homogeneous electrostatic field steric effects in gas–surface scattering can be investigated. Steric effects are measured for the direct scattering and adsorption of NO on Ag(111) and Pt(111). For direct scattering larger reflection angles are measured in case of an O‐end collision, than in case of an N‐end collision. In the experiments on adsorption/desorption it appears, that on Ag(111) adsorption is enhanced for the O‐end towards the surface, whereas on Pt(111) adsorption is enhanced for the N‐end towards the surface. The steric effects observed for NO/Ag(111) scattering, might be interpreted in terms of larger rotational excitation of the molecule with the O‐end down than in case of the N‐end down. Since the rotational excitation will mainly occur at the expense of the normal component of the incident velocity, this can explain the larger reflection angle and adsorption probability in case of an O‐end collision. This explanation is confirmed using classical trajectory calculations. The interaction between NO and Ag(111) appears to be governed by the anisotropy of the repulsive interaction. The steric effects observed for NO/Pt(111) scattering, can be partly interpreted in terms of larger phonon excitation of the molecule with the N‐end down than in case of the O‐end down. The interaction between NO and Pt(111) appears to be governed by the anisotropy of the attractive interaction.

Potential scattering in a homogeneous external electrostatic field

The problem of potential scattering in a homogeneous external electrostatic field is considered. The asymptotic behavior of the continuum wave functions in the configuration space is investigated. The scattering process is interpreted in terms of the trajectories of the asymptotic motion of the particles. The singularities of the scattering amplitude for slowly decreasing interaction potentials are studied.

A Monte Carlo simulation study of a polarizable liquid: Influence of the electrostatic induction on its thermodynamic and structural properties

An intermolecular potential function for the methyl chloride dimer which includes the electrostatic induction terms explicitly has been used in an NPT Monte Carlo statistical mechanics simulation of liquid methyl chloride at its normal boiling temperature (−23.76 °C). The nonadditive many-body induction energy is computed via an iterative procedure. It is found that the thermodynamic and structural results which are obtained with the present potential functions compare favorably with those of a previous simulation performed with effective potential functions. Modest structural changes are observed when the two simulations are compared. They mainly concern the organization around the methyl group. A detailed analysis of the electrostatic field in the liquid for both simulations shows that the mean electrostatic field is larger in the simulation with effective potential functions than with explicit induction functions. Furthermore, the induction potential functions give a more homogeneous electrostatic field within the liquid.

Potential scattering in a homogeneous electrostatic field

Potential scattering in a homogeneous electrostatic field

Das separationsvermögen des Wien-filters

A survey of the different applications of the Wien filter (crossed-field velocity analyser) is presented. The focusing properties, the mass dispersion and resolving power and the aperture error of the Wien filter with homogeneous electrostatic and magnetic deflection fields of paraxial beam are calculated. Particles entering the electric field of the Wien filter are accelerated or decelerated according to their off-axis distance, such that this change in energy limits the resolving power of the Wien filter with homogeneous fields. Calculations show that it is possible to compensate this change in velocity. A new type of Wien filter is discussed, capable of substantial beam separation by replacing the homogeneous magnetic field by a nonhomogeneous field, with changing strength due to the tapering of the pole-shoes.

Algebraic treatment of quantum-mechanical models with modified Coulomb potentials

Nonrelativistic models with modified Coulomb potentials are solved by an algebraic method based on SO(4,2) dynamical group. The nonrelativistic model with Yukawa long-range potential and the Stark effect in the nonrelativistic hydrogen atom in the homogeneous and inhomogeneous external electrostatic fields are studied in details. The algebraic method for the Dirac and Klein-Gordon relativistic hydrogen atom as well as relativistic models with the rotationally symmetric modified Coulomb potentials are also discussed.

Higher approximations to the ion distribution function and viscosity tensor for a fully ionised collisional plasma

The Boltzmann-Vlasov kinetic equation with the Landau collision term is solved for a fully ionized collisional plasma with a small beta in a homoe beta in a homogeneous magnetic and electrostatic electric field by the Mikhailovskii modified Enskog-Chapman method. In this manner the ion distribution function is obtained, as well as the viscosity tensor from the definition.

Optimum adjustment and correction of the Wien filter

The crossed homogeneous electrostatic and magnetic deflection fields of an analyser (Wien filter) have been formed by two condenser plates and two pairs of coils. The optimum operating conditions are shown to require unit magnification, contrary to the view of other authors. By varying the current ratio in the coils, a desired inhomogeneity can be introduced in the magnetic field and with this the second-order angular aberration can be corrected. The possibility of a double-focusing Wien filter is discussed.