Study on a Room-Temperature Air Plasma for Biomedical Application

Abstract

The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I$</tex></formula> – <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V$</tex> </formula> characteristics of a room-temperature atmospheric pressure air plasma are investigated. The plasma is driven by a homemade direct-current power supply. However, discharge currents appear pulsed. The pulse behavior is determined by the ion drift mechanism. The effects of the applied voltage and the gap distance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$d$</tex></formula> on pulsed repetition frequency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$f$</tex></formula> and peak value <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I_{\rm peak}$</tex></formula> of the current pulse are studied in detail. It is found that the applied voltage dramatically affects <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$I_{\rm peak}$</tex></formula> but not the pulse repetition frequency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f$</tex></formula> . When the applied voltage is higher than 12 kV, the voltage on the electrode just before breakdown starts to decrease with the increase in the applied voltage. A detail analysis shows that the residual charges play an important role in the initiation of breakdown under this condition. On the other hand, when the applied voltage is lower than 12 kV, the voltage on the electrode just before breakdown keeps constant for various applied voltages; it indicates that the residual charges play a minor role in the initiation of breakdown for this circumstance. It is found that the pulse repetition frequency is determined by the time for the ion drift to the electrode. A further analysis shows that the average electric field keeps constant for various gap distances. The pulse repetition frequency is inversely proportional to the gap distance, which is exactly observed in the experiments.