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The propagation velocity of light emission is observed to be up ~ 0.92 x 10+5 m/s along a tube of an inner diameter r o 1.5 x 10-3 m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of up ~ (4.8/ro)Da for diffusion coefficient Da along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode. [ABSTRACT FROM AUTHOR]

In this paper we present a new software package for computational simulation of single particle motion in the presence of static external electric and magnetic fields. This seemingly simple problem is in fact very complicated one. Namely, while analytic formulations of this problem are unambiguous, it is very difficult to predict even qualitatively a charged particle trajectory for an arbitrary combination of field parameters, except in simplified cases. Instead, one might perform a single particle motion simulation. Our software package represents a unique tool for this problem. A special new feature of our approach is constructing the instant Larmor Center Trajectory. For the case of slowly changing fields, the Larmor center trajectory reduces to the less general guiding center trajectory approximation. The possibilities for further investigating these two approaches by using our software might be of great interest for both educational and engineering purposes, especially in the areas of gaseous electronics and laboratory, fusion and space plasmas. [ABSTRACT FROM AUTHOR]

From the characteristics of current and voltage, the capacitive coupled external electrode fluorescent lamps are found to be similar to cold cathode fluorescent lamps having the ballast capacitors at both ends of the lamps. From the current-voltage characteristic for two types of lamps, the discharge mechanism is similar with respect to discharge process: initially a dark current, Townsend discharge with a firing voltage, followed by a normal glow. The slope and magnitude of the dark current have the same values since the gas species in the lamps are identical. At the Townsend discharge, the lamp current increases abruptly with a firing voltage of about 1 kV. In the normal glow region, the cathode fall voltage is sustained at about 600 V in the cold cathode discharge tube after Townsend breakdown at about 1 kV, while the voltage increases linearly as the current increases without negative resistance in both the external electrode lamp and the cold cathode lamp including the ballast capacitors. [ABSTRACT FROM AUTHOR]

Presents a study that predicted the dispersion of cold coupled-cavity traveling-wave tubes as well as the voltage and current characteristics for lossless and lossy multicavity electric circuits. Application of a Curnow ≡ circuit model; Development of a time-domain solution to the multicavity circuit; Numerical methods and simulation results.

Global models (GMs) have proven a key modeling tool for the plasma processing field due to simplicity and speed. However, a GM requires specification of the electron energy distribution function (EEDF). The assumption of a Maxwellian EEDF leads to inaccurate reaction rate coefficients and results in error in plasma parameter prediction in high power microwave (HPM) driven discharges. Recently, a GM was developed with a pressure-independent enhanced EEDF to improve fidelity for modeling HPM breakdown. In this work, the GM is extended to 2 decades in frequency, and the frequency effect on HPM breakdown and the EEDF is investigated. [ABSTRACT FROM AUTHOR]

A global model (GM) was developed to investigate the effect of reaction kinetics and plasma parameters on high power microwave (HPM) breakdown time for multiple species. However, the GM requires specification of the electron energy distribution function (EEDF); the common assumption of a Maxwellian EEDF results in incorrect plasma parameters since the electrons are not in equilibrium. We examine the effect of the EEDF on the GM and develop a method to obtain a better EEDF to improve the fidelity of the prediction of HPM breakdown at high pressures. [ABSTRACT FROM AUTHOR]

We demonstrate the transition characteristics and electron kinetics of microdischarges in a microgap with a cathode having microstructures using two-dimensional particle-in-cell/Monte Carlo collision (2d3v) simulations. It is found that the microdischarge is inside the hollow cavity at lower pressures, forming microhollow cathode discharges (MHCDs), while the dominant discharge moves outside the cavity at higher pressures, locating above the cathode rectangular protrusion tip. The spatial distributions of the microdischarge parameters (e.g., electric potential and electron density) are presented by capturing the transition characteristics. The electron kinetics of the microdischarges are examined based on the moment analysis of the electron Boltzmann equation. The collisional and non-collisional components of the electron power absorption are decomposed, which were seldomly investigated for microdischarges previously. The results provide fundamental insights into MHCD formation with a structured electrode at varying pressure conditions, which could be beneficial for the design and fabrication of microplasma devices in practical applications. [ABSTRACT FROM AUTHOR]

In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1–10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges. [ABSTRACT FROM AUTHOR]

Multipactor discharge near an rf window is a key limiting factor in high power microwave systems. In this work, we report special features of dielectric multipactor susceptibility under a Gaussian-type waveform as a function of the rf power density of the transverse rf electric field ( P ¯ rf ) and normal restoring field ( E dc ) via particle-in-cell (PIC) and multiple particle Monte Carlo (MC) simulations. The MC simulations show that, for a Gaussian waveform of a half peak width (Δ τ), larger than Δ τ / T = 0.15 with T = 1 ns the rf repetition period, the susceptibility boundary is similar to that of the conventional sinusoidal waveform-driven multipactor, i.e., two inclined lines in the plane of ( P ¯ rf , E dc ). However, by decreasing Δ τ , the susceptibility boundary converts to be a closed curve at Δ τ / T = 0.11 in the plane of ( P ¯ rf , E dc ) and further shrinks at Δ τ / T = 0.05. PIC simulations with a self-consistent surface and space charge effects also show a reduced E dc with increasing P ¯ rf when P ¯ rf exceeds a critical value, resulting in a closed curve in the plane of ( P ¯ rf , E dc ), and the maximum time-averaged E dc (multipactor strength) also decreases significantly with further decreasing Δ τ in agreement with MC simulations. Accordingly, the fraction of the rf power density absorbed by the multipactor discharges also decreases nonlinearly with Δ τ from the order of 10 − 2 to 10 − 3 (even 10 − 4 ), implying a significant improvement compared to the conventional sinusoidal waveform. The simulations also show that the multipactor susceptibility under a transverse Gaussian-type waveform for different frequencies follows the same scaling law in terms of the ratio of the electric field to the rf repetition rate. [ABSTRACT FROM AUTHOR]

In this work, we comprehensively investigate the generation of higher harmonic (HH) electric fields normal to the applied rf electric field in multipactor-coexisting plasma breakdown by fully kinetic particle-in-cell (PIC) simulations and a theoretical model. Firstly, a base case at driving frequency 1 GHz, transverse rf electric field amplitude 3 MV mâˆ'1, and background gas pressure 0.2 Torr, is studied in detail. The enhanced harmonic frequency observed is around ten times the fundamental rf frequency, significantly lower than the Langmuir frequency. A theoretical model reveals that the fundamental mechanism of HHs generation is streamâ€"plasma instability, which originates from stream-like secondary electron emission interacting with plasma. The resulting HH frequency and the growth rate of its oscillating amplitude from the theoretical model, agree well with the PIC simulations. With increasing pressure, the HH oscillations are found to be significantly reduced. This is because at higher pressure the gas ionization rate is higher, which causes a more rapidly increasing plasma density, leaving less time for the growth of instability. Furthermore, the parameter space in terms of background gas pressure and rf field amplitude within which the HHs appear is revealed. Finally, the effect of the driving rf frequency on HHs is also investigated, and it is found that the instability-induced oscillating HHs field remains when the driving frequency is increased to 2 GHz, however, it is highly reduced at higher driving frequency of 5 GHz, as oscillations at the fundamental frequency start playing a more important role. [ABSTRACT FROM AUTHOR]

A common approach to modeling kinetic problems in plasma physics is to represent the plasma as a set of Lagrangian macro-particles which interact through long-range forces. In the well-known particle-in-cell (PIC) method, the particle charges are interpolated to a mesh and the fields are obtained using a fast Poisson solver. The advantage of this approach is that the electrostatic forces can be evaluated in time O(N log N), where N is the number of macro-particles, but the scheme has difficulty resolving steep gradients and handling nonconforming domains unless a sufficiently fine mesh is used. The current work describes a grid-free alternative, the boundary integral/treecode (BIT) method. Using Green's theorem, we express the solution to Poisson's equation as the sum of a volume integral and a boundary integral which are computed using particle discretizations. The treecode replaces particle-particle interactions by particle-cluster interactions which are evaluated by Taylor expansions. In addition, the Green's function is regularized and adaptive particle insertion is implemented to maintain resolution. Like PIC, the operation count is O(N log N), but BIT avoids using a regular grid, so it can potentially resolve steep gradients and handle complex domains more efficiently. We applied BIT to several bounded plasma problems including a one-dimensional (1-D) sheath in direct current (dc) discharges, 1-D virtual cathode, cold two-stream instability, two-dimensional (2-D) planar and cylindrical ion optics, and particle dynamics in a Penning-Malmberg trap. Some comparisons of BIT and PIC were performed. These results and ongoing work will be reviewed. [ABSTRACT FROM AUTHOR]

An efficient grid-free numerical method is developed for particle simulations in plasma dynamics. The method relies on a treecode algorithm to solve the Poisson equation for interacting charged particles. Such algorithms have been extensively used in astrophysics, fluid dynamics, and molecular dynamics, and our aim is to assess their capability in plasma dynamics in comparison with traditional mesh-based methods such as particle-in-cell (PIC). It is well-known that PIC simulations have difficulty resolving local particle interactions within a grid cell, and we expect the gridefree treecode algorithm to have an advantage for problems involving small-scale features and highly nonuniform particle distributions. To illustrate this point we apply direct summation, treecode, and PIC methods to simulate a virtual cathode in one dimension. The treecode and PIC methods are found to be much faster than direct summation, but the treecode yields the correct solution while spurious features are present in the PIC results. The present work treats a one-dimensional problem, but the treecode algorithm generalizes directly to higher dimensions. [ABSTRACT FROM AUTHOR]

In this Letter, a multilayer-structured discharge (MSD) is reported in multipactor-coexisting plasma ionization breakdown by fully kinetic particle-in-cell simulations. The observed multilayer structure is originated by the response of ions to an electric field. It is found that the electron diffusion and multipactor discharge near the surface produce two opposite electric fields toward and away from the dielectric surface, respectively. Thus, the ions form a locally high density profile, which is followed by electron density. The lighter electrons diffuse away from the peak more quickly than the ions, resulting in an ambipolar field toward the bulk plasma region, which drives the ion density peak to propagate toward the bulk plasma. Such a process is periodically repeated, and, finally, a MSD is formed. [ABSTRACT FROM AUTHOR]