Measurement of electrical characteristics of atmospheric pressure non-thermal He plasma

This work develops a method for determining the electrical characteristics of an atmospheric pressure non-thermal He plasma. It is applied on an original low power plasma source that has some specific properties, as follows: (1) it uses high sinusoidal voltages generated in an LRC series resonant circuit; (2) the frequency of the sinusoidal waveform that maintains the discharge (< 1 MHz) is lower than those used till now (> 13.56 MHz); (3) the circuit is powered with dc voltages lower than 5 V and dc currents up to 1 A; and (4) the plasma torch is made of the usual materials and has a single electrode. As a function of the power and the gas (helium) flow rate, the generated plasma has three developing stages: pointed, extended (oval ball) and jet. The developed calculation algorithm of the electrical characteristics of the plasma uses only the parameters that can be measured without disturbing the plasma. The algorithm was validated by direct measurement of the plasma current. The electrical measurements show that the plasma has a purely resistive behaviour. As a function of the absorbed power and the gas flow rate, the plasma resistance varies in the range of 10(4)-10(5) ohm.