John P. Verboncoeur

An object-oriented electromagnetic PIC code

Abstract The object-oriented paradigm provides an opportunity for advanced PIC modeling, increased flexibility, and extensibility. Particle-in-cell codes for simulating plasmas are traditionally written in structured FORTRAN or C. This has resulted in large legacy codes which are difficult to maintain and extend with new models. In this ongoing research, we apply the object-oriented design technique to address these issues. The resulting code architecture, OOPIC (object-oriented particle-in-cell), is a two-dimensional relativistic electromagnetic PIC code. The object-oriented implementation of the algorithms is described, including an integral-form field solve, and a piecewise current deposition and particle position update. The architecture encapsulates key PIC algorithms and data into objects, simplifying extensions such as new boundary conditions and field algorithms.

Particle Simulation of Plasmas: Review and Advances

Particle simulation of plasmas, employed since the 1960s, provides a self-consistent, fully kinetic representation of general plasmas. Early incarnations looked for fundamental plasma effects in one-dimensional systems with ~102–103 particles in periodic electrostatic systems on computers with 100 kB memory. Recent advances model boundary conditions, such as external circuits to wave launchers, collisions and effects of particle–surface impact, all in fully relativistic three-dimensional electromagnetic systems using ~106–1010 particles on massively parallel computers. While particle codes still enjoy prominance in a number of basic physics areas, they are now often used for engineering devices as well.

Advances in modeling and simulation of vacuum electronic devices

Recent advances in the modeling and simulation of vacuum electronic devices are reviewed. Design of these devices makes use of a variety of physical models and numerical code types. Progress in the development of these models and codes is outlined and illustrated with specific examples. The state of the art in device simulation is evolving to the point such that devices can be designed on the computer, thereby eliminating many trial and error fabrication and test steps. The role of numerical simulation in the design places can be expected to grow further in the future.

Transition of window breakdown from vacuum multipactor discharge to rf plasma

In high-power microwave systems, the transition of window breakdown from single surface vacuum multipactor discharge to rf plasma with increasing gas pressure is investigated using particle-in-cell simulations. An intermediate pressure regime where multipactor discharge and rf plasma coexist was found. The pressure range where the multipactor can be maintained is summarized in the plot of the secondary electron emission yield as a function of the gas pressure. As the gas pressure increases, electron-neutral collisions prevail against secondary electron emissions and the electron energy probability function changes from the bi-Maxwellian at low pressures to Druyvesteyn at high pressures as a result of the change in electron heating and cooling processes. The discharge formation time in argon, neon, and xenon is shown for different gas pressures. Different scaling laws in the discharge formation time are presented at low and high pressures, respectively.

Scaling laws for dielectric window breakdown in vacuum and collisional regimes

The scaling laws for the initiation time of radio frequency (rf) window breakdown are constructed for three gases: Ar, Xe, and Ne. They apply to the vacuum, to the multipactor-triggered regime, and to the collisional rf plasma regime, and they are corroborated by computer simulations of these three gases over a wide range of pressures. This work elucidates the key factors that are needed for the prediction of rf window breakdown in complex gases, such as air, at various pressures.

Space-charge effects on multipactor on a dielectric

Analyzes the effects of space charge shielding on the steady state of a multipactor discharge on a dielectric. Analytic methods are used to obtain an exact function for the potential in the discharge, assuming a Maxwellian distribution of emitted electrons. An equation for the amount of power deposited on the dielectric by the multipactoring electrons, for a given saturation level, is given. A simple method for obtaining the saturation level, for a given material, is obtained.

A one‐dimensional collisional model for plasma‐immersion ion implantation

Plasma‐immersion ion implantation (also known as plasma‐source ion implantation) is a process in which a target is immersed in a plasma and a series of large negative‐voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A general one‐dimensional model is developed to study this process in different coordinate systems for the case in which the pressure of the neutral gas is large enough that the ion motion in the sheath can be assumed to be highly collisional.

Time-dependent physics of a single-surface multipactor discharge

The time-dependent physics of the single-surface multipactor is investigated by using both particle-in-cell (PIC) and Monte Carlo (MC) simulations. An oscillation of the normal surface field and number of electrons at twice the rf was observed in the PIC code. The temporal relationship between the fields normal and parallel to the surface traces a closed curve in the ac saturation state. The shape of the curve depends on the amplitude of the rf electric field normalized to the rf (normalized electric field). In comparison with the PIC simulation result, the oscillation in the MC simulation appears only when the normalized electric field is so large that the time step of the MC simulation is smaller than the rf period.

Transition from Fowler-Nordheim field emission to space charge limited current density

The Fowler-Nordheim law gives the current density extracted from a surface under strong fields, by treating the emission of electrons from a metal-vacuum interface in the presence of an electric field normal to the surface as a quantum mechanical tunneling process. Child’s law predicts the maximum transmitted current density by considering the space charge effect. When the electric field becomes high enough, the emitted current density will be limited by Child’s law. This work analyzes the transition of the transmitted current density from the Fowler-Nordheim law to Child’s law space charge limit using a one-dimensional particle-in-cell code. Also studied is the response of the emission model to strong electric fields near the transition point. We find the transition without geometrical effort is smooth and much slower than reported previously [J. P. Barbour, W. W. Dolan, J. K. Trolan, E. E. Martin, and W. P. Dyke, Phys. Rev. 92, 45 (1953)]. We analyze the effects of geometric field enhancement and work f...

Global modeling of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel

A global model of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel was developed. This model was used to evaluate electron temperature, plasma density, densities of excited state atoms, wall charge density, current density, excimer density, and vacuum ultraviolet (VUV) intensity, and their gas composition-pressure dependencies, in order to analyze the mechanism of VUV radiation and discharge efficiency. The results show that the intensity ratio of 173 to 147 nm VUV is about a few percent. This means that the contribution of excimers is small in terms of VUV radiation. The maximum discharge efficiency was about 9% for Xe fraction in the range of 2%–12% and gas pressure in the range of 100–600 Torr. Discharge efficiency increases in the high Xe fraction and gas pressure region. The increase of the discharge efficiency is attributed to a decrease of discharge current and an increase of Xer*(3P1) excited state atom, due to the low electron temperature in the hig...