Recent diagonostic results for the steady state - DC atmospheric pressure plasma discharge

Summary form only given. We have made the following advances for our DC, steady state atmospheric pressure plasma discharge in air. We have measured the free electron concentration in our discharge by converting the 1/2 cm. gap, parallel-plate discharge into a parallel-plate transmission line. The frequency used was 6 GHz, corresponding to a free-space wavelength of 15 cm. The path length for the microwaves in the plasma was about 15 cm. The discharge was pulsed to high current (about 50 mA) using a capacitor bank and a spark gap. Under these conditions, a collisional attenuation of 20% was observed, yielding a free electron concentration of about 1 exp 12 electrons per cc. Extrapolating to the usual steady-state discharge operating conditions of 10 mA, we conclude that the normal operating free electron density is about 2 exp 11 electrons per cc, agreeing with earlier probe estimates. Note that at atmospheric pressure and the frequency used, the plasma is resistive, not reactive. We note that the attenuation decays in time on the order of 10 microseconds after each pulse. We attribute this decay of the attenuation to the recombination of the free electrons to form negative ions. Previous probe experiments reveal negative-positive ion plasma of 1 exp 12 ions per cc. We have replaced the water in our water-loaded conducting ceramic electrode with a 30% hydrogen peroxide solution. The net result is that a multisecond second exposure completely eliminates all E-coli bacteria on our test Petri dishes, although we have increased the initial bacteria concentration by a factor of one million (over one hundred million initial bacteria per plate). We have found that the sterilizing effect penetrates through normally sealed mailing envelopes. In conclusion, we have found that the free electron density in DC atmospheric pressure air plasma can be measured easily using a transmission line technique. Also using hydrogen peroxide instead of water in the moistened ceramic electrode can enhance the sterilizing effect of the DC atmospheric pressure discharge