AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Monday Sessions
       Session PS2-MoA

Paper PS2-MoA7
Electron Current Extraction from rf Micro-Dielectric Barrier Discharges

Monday, October 18, 2010, 4:00 pm, Room Galisteo

Session: Atmospheric Plasma Processing and Micro Plasmas
Presenter: J.-C. Wang, University of Michigan, Ann Arbor
Authors: J.-C. Wang, University of Michigan, Ann Arbor
N. Leoni, Hewlett Packard Research Labs
O. Gila, Hewlett Packard Research Labs
M.J. Kushner, University of Michigan, Ann Arbor
Correspondent: Click to Email
Micro dielectric barrier discharges (mDBD’s) consist of micro-plasma devices (10-100 μm diameter) in which the electrodes are fully or partially covered by dielectrics, and operate at atmospheric pressure driven with radio frequency (rf) wave forms. After the plasma is generated charging of the dielectric terminates the discharge. At atmospheric pressure, particularly in attaching gases, the plasma formation and decay times can be as short as a few to tens of ns whereas the rf period may be tens to hundreds of ns. So the micro-plasma may need to be re-ignited with each discharge pulse. 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 mDBD and the electron emitting properties are important to its operation. In this presentation, we will discuss the properties of mDBD’s sustained in atmospheric pressure N2 and air using results from a two-dimensional plasma simulation. The micro-DBD’s are sandwich structures with an opening of ten-of-microns excited with rf voltage waveforms of up to 25 MHz up to 0.5 mm away. The model, nonPDPSIM, solves Poisson’s equation and transport equations for charge species and electron energy conservation equation for electron temperature. Rate coefficients and transport coefficients are obtained from local solutions of Boltzmann’s equation for the electron energy distribution. Radiation transport is addressed using a Green’s function approach. We find that following avalanche by electron impact ionization in the mDBD cavity, the plasma can be expelled from the mDBD’s cavity towards the collection electrode during the part of the rf cycle when the collection electrode appears anodic. This extraction can be enhanced by biasing the extraction electrode. At lower frequencies, the plasma needs to be reformed every cycle. Long lived neutral species facilitate the generating of plasma by production of UV photons that continuously seed secondary electrons at surfaces until the potential is favorable to re-ignite plasma. The amount of extracted charge per pulse is not a strong function of rf frequency for values up to 25 MHz, but is sensitive to the dielectric constant of the barrier. For applied voltages of up to 2-3 kV, electric field emission appears not to play an important role.