Publications

Proposed for publication in Physical Review E.

Hebner, Gregory A.; Hebner, Gregory A.; Riley, Merle E.

Abstract not provided.

Proposed for publication in Physical Review E.

Hebner, Gregory A.; Hebner, Gregory A.; Riley, Merle E.

The magnitude and the structure of the ion-wakefield potential below a negatively charged dust particle levitated in the plasma-sheath region have been determined. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy dust collisions in a well-defined electrostatic potential, which constrained the dynamics of the collisions to be one dimensional. The peak attraction was on the order of 100 fN. The structure of the ion-wakefield-induced attractive potential was significantly different from a screened-Coulomb repulsive potential.

Riley, Merle E.; Buss, Richard J.; Hopkins, Matthew M.; Miller, Paul A.; Moats, Anne R.; Wampler, William R.; Buss, Richard J.

This report documents the strategies for verification and validation of the codes LSP and ICARUS used for simulating the operation of the neutron tubes used in all modern nuclear weapons. The codes will be used to assist in the design of next generation neutron generators and help resolve manufacturing issues for current and future production of neutron devices. Customers for the software are identified, tube phenomena are identified and ranked, software quality strategies are given, and the validation plan is set forth.

Riley, Merle E.; Hebner, Gregory A.

Abstract not provided.

Riley, Merle E.

A model is developed for the forces acting on a micrometer-size particle (dust) suspended within a plasma sheath. The significant forces acting on a single particle are gravity, neutral gas drag, electric field, and the ion wind due to ion flow to the electrode. It is shown that an instability in the small-amplitude dust oscillation might exist if the conditions are appropriate. In such a case the forcing term due to the ion wind exceeds the damping of the gas drag. The basic physical cause for the instability is that the ion wind force can be a decreasing function of the relative ion-particle velocity. However it seems very unlikely the appropriate conditions for instability are present in typical dusty plasmas.

Journal of Physics B: Atomic, Molecular and Optical Physics

Riley, Merle E.; Ritchie, A.B.

Hydrogen atom-hydrogen atom scattering is a prototype for many of the fundamental principles of atomic collisions. In this work we present the formalism and the predictions of a time-dependent self-consistent-field description of the H + H system for scattering in the intermediate energy regime of 1-100 keV. Because of the unrestricted nature of the numerical orbital description, this method includes the effects of an unlimited basis set within each orbital. Electron exchange and a limited amount of electron correlation are included as well. We solve numerically coupled three-dimensional Schrodinger equations for the two-electron orbitals in singlet and triplet symmetries. Excitation and ionization cross sections are computed and compared with other theory and experiment. The results capture many features of the problem but illustrate a need for more quantitative experimental information concerning the H + H system in this energy range.

Journal of Vacuum Science and Technology

Woodworth, Joseph R.; Riley, Merle E.; Amatucci, Vincent A.; Hamilton, Thomas W.; Aragon, Ben P.

In this paper, the authors report the absolute intensities of ultraviolet light between 4.9 eV and 24 eV ( 250 nm to 50 mn ) striking a silicon wafer in a number of oxide-etch processing discharges. The emphasis is on photons with energies greater than 8.8 eV, which have enough energy to damage SiO{sub 2}. These discharges were in an inductively-driven Gaseous Electronics Conference reference cell which had been modified to more closely resemble commercial etching tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the VUV light in these discharges is strongly trapped. For the pure halocarbon gases examined in these experiments (C{sub 2}F{sub 6}, CHF{sub 3}, C{sub 4}F{sub 8}), the fluxes of VUV photons to the wafer varied from 1 x 10{sup 15} to 3 x 10{sup 15} photons/cm{sup 2} sec or equivalently from 1.5 to 5 mW/cm{sup 2}. These measurements imply that 0.1% to 0.3% of the rf source power to these discharges ends up hitting the wafer as VUV photons for the typical 20 mT, 200 W rf discharges. For typical ashing discharges containing pure oxygen, the VUV intensities are slightly higher--about 8 mW/cm{sup 2} . As argon or hydrogen diluents are added to the fluorocarbon gases, the VUV intensities increase dramatically, with a 10/10/10 mixture of Ar/C{sub 2}F{sub 6}/H{sub 2} yielding VUV fluxes on the wafer 26 mW/cm{sup 2} and pure argon discharges yielding 52 mW/cm{sup 2} . Adding an rf bias to the wafer had only a small effect on the VUV observed through a side-port of the GEC cell.