Analysis of a nano-pulsed DBD Plasma jet for endoscopy and impact of excitation parameters

Abstract

Cold atmospheric plasma induces various dose-dependent effects on living cells, from proliferation to necrosis. These effects are of interest in the field of therapeutic flexible endoscopy, although implementing an effective plasma delivery system represents a technical challenge. This work studies the impact of critical parameters on plume intensity, delivered reactive species (RS), and current administered to the target for the use of plasma in endoscopy. A 2 m long dielectric barrier discharge plasma jet was studied upon nano-pulsed high voltage excitation to increase plasma reactivity. The peak voltage, gas gap, pulse repetition frequency, and pulse width were varied while the power dissipated by the system and the optical emissions (with imaging and spectrometry) were measured. Two configurations were compared: the first one with the plume exiting freely in air, and the second one with the plume impinging an electrical equivalent of the human body. Finally, the current flowing through the capillary was measured at regular intervals along the tube with a Rogowski coil. Results show that (a) a conductive target increases the ratio of RS produced over the dissipated power, (b) increasing the pulse repetition frequency does not improve the RS production per pulse (e.g. through a synergetic, memory effect), (c) increasing the pulse width does not influence RS production but increases the dissipated power, and (d) current linearly leaks through the tube walls, and leaks are lower with nano-pulsed compared to sinusoidal excitation. Reactance and capacitance values of the system are analyzed based on the electrical equivalent circuit approach. Finally, displacement and discharge currents are discussed to bring power dissipation mechanisms to light and compare them between configurations. The conclusions drawn are important for the future design of safe and effective endoscopic plasma devices.