Simulation of atmospheric pressure ionization waves propagating through flexible capillary tubes and impinging onto a target

Summary form only given. Atmospheric pressure, low temperature plasmas (APPs) have are being investigated for biomedical applications such as sterilization, wound healing, cell manipulation and cancer therapy. The generation and propagation of APPs in a flexible capillary tube not only has direct applications, such as catheter sterilization, but also provides a viable way of transporting plasma and its active species to remote, specific targeted areas. When incorporated with various endoscopic devices, remotely delivered plasmas through capillaries potentially open new door for treating internal disease with APPs. To investigate their fundamental properties, we carried out numerical simulations of the generation of APPs by posi tive and negative voltage pulses, their rapid propagation through long, flexible and bent capillary tubes (20 cm length, 500 μm wide, 400:1 aspect ratio) in the form of an ionization wave, and their final exit from the capillary tube, impinging onto a target. Different gas mixtures, including Ne/Xe=99/1 were investigated. The numerical simulation platform is nonPDPSIM, a 2-dimensional plasma hydrodynamics model with radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coinci dent with the electron energy equation with transport coeffi cients obtained from solutions of Boltzmann's equation. The ionization front in the capillary appears to be bullet like and its propagation speed varies between l-5xl07 cm-s"1 as it traverses different capillary sections with varying radii and directions of curvature slower for small radii and con cave paths. These trends are likely a consequence of surface charging and the extent of photoionization ahead of the ava lanche front. The plasma tends to hug the walls of the smaller curvature, changing from side-to-side to follow the smaller curvature. Propagation speeds are a function of the width of the capillary. The electrical structure of the ionization front, including the electrical field, electron density and electron temperature will be discussed. The impingement of the exiting ionization front on the target and the resulting density distribution of various charged and neutral species will also be discussed.