| AVS 56th International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS2-TuM |
| Session: | Atmospheric Plasma Processing and Microplasmas |
| Presenter: | J. Hopwood, Tufts University |
| Authors: | J. Hopwood, Tufts University Z. Zhang, Tufts University |
| Correspondent: | Click to Email |
Instabilities in atmospheric pressure plasmas are responsible for the irreversible glow-to-arc transition of cold microplasmas into destructive arcs. DC microplasmas are usually stabilized using a ballast resistor. Alternatively, AC microplasmas are controlled by rapidly extinguishing the discharge through the electrical charging of dielectric barriers surrounding the electrodes (i.e., the DBD). The negative differential resistance of the glow-to-arc region also makes parallel operation of plasmas difficult. Stable arrays of DC and AC microplasmas, however, are possible using distributed ballasting1. In this work, we stabilize the individual microplasma using a quarter-wave resonator constructed from a microstrip transmission line. As the microwave input power increases, the microplasma’s electrical resistance drops and the resonator is automatically quenched; thus arcing is avoided. Microwave impedance spectroscopy measures the plasma resistance as a function of input power and confirms the negative differential resistance of the microplasma. The technical challenge to operate multiple microwave resonators is met by employing coupled-mode theory2. An array of high-Q resonators will couple energy efficiently among themselves provided that all resonators share a common resonance frequency. A single microwave power source (400 MHz, 4 watts) drives the first resonator in a linear array and the remaining undriven resonators redistribute the input energy such that multiple microplasmas operate in a stable, parallel manner. Solutions to the classic coupled-mode theory equations are compared with electromagnetic simulations of the resonator array and with the observed excitation of multiple microplasmas. Having confirmed that coupled-mode theory is applicable to microplasma arrays, we then demonstrate the production of stable, high density (ne > 1014 cm-3) cold atmospheric pressure plasma in a linear configuration that is suitable for high-rate material processing.
1 K. H. Becker, K. H. Schoenbach and J. G. Eden, J. Phys. D: Appl. Phys. 39, R55 (2006).
2 H. A. Haus and W. Huang, Proc. IEEE 19, 1505 (1991).