David B. Boercker

Modeling plasma flow in straight and curved solenoids

The ‘‘flux‐tube’’ model originated by Morozov is a very simple and numerically efficient method for simulating ion motion in plasma filters. In order to test its utility as a design tool, we compare the predictions of the model to recent experimental measurements of plasma flow in both straight and curved solenoids.

Simulating growth of Mo/Si multilayers

Multilayer structures of alternating thin layers of molybdenum and silicon are of great interest as x‐ray optics components and a considerable amount of effort has been expended in their development. The efficiencies of these structures depend upon both the accurate control of the layer thicknesses and the sharpness in the interface between layers. High‐ resolution electron microscopy reveals that the interface created by deposition of Mo on Si is much more diffuse than that produced by depositing Si on Mo. We have used molecular dynamics to simulate the deposition processes and observe significant penetration of the Si substrates by the incident Mo atoms, while incident Si atoms remain on the surface of the Mo substrate.

Degenerate quantum gases in the binary collision approximation

Abstract A binary collision approximation is used to close the second equation of the BBGKY hierarchy for the reduced density matricies, providing a simple but accurate description of the equilibrium and non-equilibrium properties of a low-density quantum gas. In particular, the resulting approximate equations describe the degeneracy effects associated with Bose-Einstein or Fermi-Dirac statistics. The equilibrium two-particle density matrix and pressure agree with those implied by Martin and Schwinger for strong degeneracy and with those of Beth and Uhlenbeck for weak degeneracy. For non-equilibrium properties, solution of the equation for the two-particle density matrix allows closure of the first equation, resulting in a prototype of the non-linear Boltzmann or Uehling-Uhlenbeck kinetic equation. Limits leading to these latter equations are discussed.

Plasma transport in a new cathodic arc ion source, theory and experiment

Abstract We have developed a plasma transport code based upon the “flux tube” model and applied it to the ion transport in a recently developed metal-ion source based on the cathodic vacuum arc. This model is compared with ion current measurements made at various locations within the source. The agreement is sufficient to justify use of this model for future arc source design.

Correlations in the quantum theory of plasma line broadening

Abstract A unified theory of plasma line broadening is obtained from a quantum kinetic equation, paralleling existing results for a classical plasma. The atom-electron interactions are shielded by equilibrium electron correlation functions and a frequency dependent dielectric function. A “ring” approximation is used to replace the classical plasma parameter expansion, for typical laboratory conditions. Atom-electron correlations are included as well as electron-electron correlations.

Effective interatomic potential for body‐centered‐cubic metals

An effective interatomic potential suitable for all body‐centered‐cubic (bcc) metals is developed based on the embedded atom method. The potential predicts all major anomalies displayed in the phonon spectra of the bcc transition metals, as well as the large relaxation of the (100) surface of V, Nb, and Ta.

Classical and quantum kinetic equations with exact conservation laws

Stationary and dynamic properties of reduced density matrices can be determined from formal or approximate closures of an infinite hierarchy of equations. The local macroscopic conservation laws place weak but important constraints on the reduced density matrices which should be respected by any closure. For pairwise additive forces conditions on the closure of the one- and two-particle equations are obtained that preserve the exact functional dependence of the conserved densities and their fluxes on the reduced density matrices. To illustrate the nature of these conditions, a closure approximation suitable for a quantum gas is given, yielding an extension of the time-dependent Hartree-Fock equations for the dynamics of a nuclear fluid to include collisions.

Simulation of the growth of Mo/Si multilayers

The successful development of soft x-ray projection lithography will depend heavily on the production of efficient, durable optical components. A leading candidate for x-ray mirrors near 130 angstrom is multilayer structures made of alternating thin layers of Mo and Si. High- resolution electron microscopy reveals that the interface created by deposition of Mo on Si is much more diffuse than that produced by depositing Si on Mo. We have performed molecular dynamics simulations of the deposition process and observed significant penetration of the Si substrates by incident Mo atoms while Si atoms remain on the surface of the Mo substrates.

Rigid-rotor models of plasma flow

Publisher Summary This chapter discusses the theoretical underpinnings of rigid-rotor type models of plasma flow. The chapter discusses the theoretical basis for the flux-tube model and compare its predictions to three sets of experimental data. The chapter includes rigid-rotor equilibria, Aksenovs filter and the dome source. Plasma equilibria of the rigid-rotor type were first investigated in detail by Davidson. Rigid-rotor equilibria have been experimentally produced and extensively studied in vacuum arc centrifuges. In these systems, plasma about one meter long and 5 cm in diameter is produced in a long solenoid. The electron densities are about 1014 cm-3 and the ion temperatures are about 3 eV. The measured potentials are found to be quadratic, except near the solenoid walls, and the density profiles are well described by Gaussians centered on the axis. The rigid-rotor frequencies are measured to be about 105 rad/s, and correspond to the slow mode. The fast mode has never been observed in these devices, but the existence and nature of rigid-rotor equilibria in vacuum arc plasmas appear to be well established both experimentally and theoretically. A rigid-rotor model has also been used to describe collective focusing of ion beams in thin magnetic lenses and in solenoidal fields.

Models for spectral line shapes from ions in strongly coupled plasmas

Abstract Two models for calculating spectral line shapes from ions in strongly coupled plasmas are proposed. It is assumed that the dominant radiator-plasma coupling is due to monopole and dipole interactions, so that the plasma environment can be characterized by its microscopic electric field at the radiator. A primary objective here is to describe the effects of ion motion (for both radiator and perturbers) near the line center. The first model is formulated in terms of ion field dynamics with electron collisional broadening. The second model is a symmetric formulation of ion and electron field dynamics.