Propagation dynamics of a helium micro-tube plasma: Experiments and numerical modeling.

Micro-Tube Plasmas (μTP) have been gaining attention for applications ranging from medicine to material science and analytical chemistry due to their small size, low cost of operation and flexibility. In the present work a specific μTP, known as the Flexible Micro Tube Plasma (FμTP) is investigated experimentally and, for the first time, numerically as well. The creation, propagation mechanisms and properties of the ionization waves inside the microtube are investigated during the positive and negative half cycle of a μs square wave applied voltage. A two-dimensional (2D) axi-symmetric numerical model is developed and compared with optical emission spectroscopy showing good agreement. During the positive half cycle the plasma propagates as an ionization wave (or streamer) depositing charges on the dielectric wall. During the negative half cycle the plasma propagates due to the neutralization of those surface charges on the walls. The different propagation mechanisms affect the accumulation of charges, the induced electric field, and the speed of the ionization waves. [Display omitted] • The microtube plasma is an efficient and low voltage ambient MS soft ionization source. • The discharge during the rising voltage resembles a plasma streamer. • The discharge during the falling voltage is much faster and is due to leftover charges on the wall. • There is a glow discharge from the electrode to the wall during the falling voltage. [ABSTRACT FROM AUTHOR]