| Popis: |
Summary form only given. A fast-pulsed, UV laser-initiated, RF-sustained high pressure plasma source has been developed and optimized for more efficient large volume (ges1000 cc), high pressure plasma generation. We have shown that during the tast-pulsed plasma formation, the plasma load impedance as seen by the helical antenna varies significantly from 0.5+j125 Omega to 4.0+j130 Omega on short time scales. As a result, it presents a challenge to the RF matching system. In order to ensure efficient RF power coupling to the plasma, a dynamic RF impedance measurement and matching technique has been designed and implemented: a dual directional coupler is used to precisely measure the complex incident RF reflection coefficient at the input end of the matchbox. A pair of high voltage probes is used to monitor the time-dependent plasma impedance so that the matching circuit can be tuned accordingly to match the varying plasma load impedance. As a result of this effort, a large volume (1500 cc), high electron density (1.6times1011 /cc) laser-initiated, RF-sustained high pressure (50 torr) air constituents plasma is created utilizing an initiating UV laser pulse energy of 100 mJ and subsequently maintained by a net RF power level of 3 kW for several seconds. The RF power budget is 2 Watts/cc. Optical emission spectroscopy is used to analyze the plasma, aided by the Specair program developed by Laux et al. The rotational temperature of N2 C-B (second positive) is obtained by matching the experimental spectrum results with the Specair code-simulated results. Time evolution of the plasma's electron density and total electron-neutral collision frequency is diagnosed using a millimeter wave interferometry technique. A new mathematical method is developed to compute the time-dependent electron density and total electron-neutral collision frequency, and subsequently to evaluate electron temperature levels based on the interferometric experimental results. |
