Influence of pulse width on the creation of ions in an atmospheric-pressure plasma jet

Abstract

Summary form only given. Atmospheric-pressure plasma jets are used extensively for biomedical applications e. g. plasma-sterilization, -wound healing [1] and biomaterial surface modification [2]. To elicit the desired biological response it is highly desirable to optimize the key species produced in the discharge such as NO and OH radicals, OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> and NO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions. Recently, time-resolved atmospheric mass spectrometry [3] revealed that the generation of positive and negative ionic species is correlated to the positive and negative current peaks in a sinusoidal excited dielectric barrier plasma jet. Further to this, the lifetime of the negative ions in the jet is longer than the positive species e. g. decay time constants τ~20 μs for the negative ions and ~10 μs for the positive ions.In this contribution a dielectric barrier plasma jet is excited using monopolar high voltage pulses. Positive and negative current peaks are generated on the rising and falling edges respectively. By varying the duty cycle of the pulsed waveform it is possible to control the time delay between the positive and negative current peaks providing a route to modulate of the ionic content of the discharge. Time-resolved mass spectrometry results indicate that large duty cycles (>;75%) favour the generation of NO± ions accompanied with a significant reduction in negative ion formation.