Napoleon J. Leoni

Electron current extraction from radio frequency excited micro-dielectric barrier discharges

Micro dielectric barrier discharges (mDBDs) consist of micro-plasma devices (10–100 μm diameter) in which the electrodes are fully or partially covered by dielectrics, and often operate at atmospheric pressure driven with radio frequency (rf) waveforms. In certain applications, it may be desirable to extract electron current out of the mDBD plasma, which necessitates a third electrode. As a result, the physical structure of the m-DBD and the electron emitting properties of its materials are important to its operation. In this paper, results from a two-dimensional computer simulation of current extraction from mDBDs sustained in atmospheric pressure N2 will be discussed. The mDBDs are sandwich structures with an opening of tens-of-microns excited with rf voltage waveforms of up to 25 MHz. Following avalanche by electron impact ionization in the mDBD cavity, the plasma can be expelled from the cavity towards the extraction electrode during the part of the rf cycle when the extraction electrode appears anodi...

Charging of moving surfaces by corona discharges sustained in air

Atmospheric pressure corona discharges are used in electrophotographic (EP) printing technologies for charging imaging surfaces such as photoconductors. A typical corona discharge consists of a wire (or wire array) biased with a few hundred volts of dc plus a few kV of ac voltage. An electric discharge is produced around the corona wire from which electrons drift towards and charge the underlying dielectric surface. The surface charging reduces the voltage drop across the gap between the corona wire and the dielectric surface, which then terminates the discharge, as in a dielectric barrier discharge. In printing applications, this underlying surface is continuously moving throughout the charging process. For example, previously charged surfaces, which had reduced the local electric field and terminated the local discharge, are translated out of the field of view and are replaced with uncharged surface. The uncharged surface produces a rebound in the electric field in the vicinity of the corona wire which in turn results in re-ignition of the discharge. The discharge, so reignited, is then asymmetric. We found that in the idealized corona charging system we investigated, a negatively dc biased corona blade with a dielectric covered ground electrode, the discharge is initially sustained by electron impact ionization from the bulk plasma and then dominated by ionization from sheath accelerated secondary electrons. Depending on the speed of the underlying surface, the periodic re-ignition of the discharge can produce an oscillatory charging pattern on the moving surface.

Glow-like atmospheric pressure micro-discharges produced by charge rollers

Summary form only given. Conductive charge rollers (CR) are used in print engines for surface charging of the cylindrical photoconductor (PC) at atmospheric pressure. The charging process is essentially a dielectric-barrier-discharge (DBD). Microplasmas are produced in the narrowing gap between the CR and PC, which then charges the PC. The streamer-like plasmas can be terminated by surface charging of the PC if operated with a dc or quasi-dc voltage on the CR. From a practical matter, the surfaces of both the CR and PC are rotating. The rotation of the PC brings in uncharged surface which reestablishes the voltage between the CR and PC, and re-ignites the plasma. As a result, a periodic charging pattern on the PC surface may be formed. Under certain operating conditions, a glow-like discharge was simulated in the CR and a quasi-dc current was collected on the PC surface. These behaviors and the uniformity of surface charging are sensitive to the speed of the PC and applied voltage.In this presentation, we will discuss the behavior of atmospheric pressure microplasmas sustained in air between the CR and PC, and the charging properties on the PC surface using results from a 2-dimensional simulation. The model, nonPDPSIM, solves Poissons equation and transport equations for charge and neutral species and the electron energy conservation equation for electron temperature. A Monte Carlo simulation is used for tracking sheath accelerated electrons. Rate and transport coefficients for bulk electrons are obtained from local solutions of Boltzmanns equation for the electron energy distribution. Radiation transport is addressed using a Greens function approach.

Electron Current From an RF Microdielectric Barrier Discharge

Nonarcing microdielectric barrier discharges (mDBDs) using radio-frequency excitation are attractive in that the arrays of devices can be inexpensively produced to generate surface sources of plasma or radicals. Images of the time evolution of electron extraction from an mDBD sustained in atmospheric-pressure N2 are presented.

Modeling of micro-dielectric barrier discharges

Summary form only given. Arrays of micro-plasmas having dimensions of tens to hundreds of microns are finding use as sources of radicals and charged particles in addition to their conventional use as photon sources. In one variant of these devices, the electrodes are fully or partially covered by dielectrics, and so they operate as dielectric barrier discharges (micro-DBDs). As such, the devices must be pulsed or driven with high frequency (HF) waveforms. When operating at atmospheric pressure in air, the plasma formation and decay times can be as short as tens of ns, and so the plasma may need to be re-ignited with each discharge pulse. In this situation, the physical structure of the micro-DBD and the electron emitting properties are important to its operation.In this presentation, we will discuss the properties of microDBDs sustained in atmospheric pressure N2 and air using results from a 2-d plasma simulation. The micro-DBDs are sandwich structures with openings of tens-of-microns excited with HF voltage waveforms. The model includes solution of Poissons equation, transport of charged and neutral species, radiation transport, electron photo-emission from surfaces, and beam transport of secondary electrons. We found that, depending on the details of the voltage waveform and surrounding structures, the plasma can be expelled from the micro-DBD cavity during one part of the HF cycle, thereby requiring the plasma to be reformed later in the cycle. This expulsion is partly facilitated by the Debye length being larger (in some cases) than the DBD cavity. Long lived neutral species in the plasma can facilitate restart by production of secondary electrons from surfaces. For example, UV photon emission from long lived states continuously provides seed secondary electrons at surfaces until the potential is favorable to generate the plasma.