Chemical mechanisms inducing a dc current measured in the flowing post-discharge of an RF He-O2 plasma torch

TL;DR

This study investigates the mechanisms behind a dc current observed in the post-discharge of an RF helium-oxygen plasma torch, revealing Penning ionization as a key factor influenced by gas flow rates and distance from the surface.

Contribution

It provides new insights into the chemical processes inducing dc current in RF plasma torch post-discharges, highlighting the role of Penning ionization and experimental parameters.

Findings

DC current of 1-20 A observed in post-discharge.

Penning ionization identified as the main mechanism.

Gas flow rates and distance affect the current.

Abstract

The post-discharge of an RF plasma torch supplied with helium and oxygen gases is characterized by mass spectrometry, optical emission spectroscopy and electrical measurements. We have proved the existence of a dc current in the post-discharge (1--20 A), attributed to the Penning ionization of atmospheric nitrogen and oxygenated species. The mechanisms ruling this dc current are investigated through experiments in which we discuss the influence of the O2 flow rate, the He flow rate and the distance separating the plasma torch from a material surface located downstream.