Active species evolution in presence of different targets impacted by helium plasma jet at atmospheric pressure

A low-temperature plasma jet is generated by a dielectric barrier discharge poweredby a pulsed high voltage in helium flow (3 L/min) at atmospheric pressure inpresence of different targets (glass slide or ultra-pure water or a grounded metal plate)positioned perpendicular to the plasma propagation axis. Experimental electricalcharacterizations as discharge current, voltage and powerand optical ones as intensifiedcamera ICCD, Schlieren imaging and emission spectroscopy to follow specific excitedspecies have been achieved. The transition from laminar to turbulent regime wereobserved during the discharge ignition with a larger spreading of the plasma on thesurface target with lower dielectric permittivity and the generation of two dischargesduring each voltage pulse is highlighted during the propagation of the ionization wavethat has shown a variable speed along the plasma axis not depending on the target kind.The evolution of some active species (as OH, O and excited nitrogen and helium) areinvestigated using time resolved mapping of the emissions of radiative excited speciespropagating in ambient air between the plasma jet output andthe target. For a lowrelative permittivity target (glass), the volume ionization wave at its arrival on thetarget spreads on its surface thus behaving as a surface ionization wave. For thehighest relative permittivity (metal), a conductive channel appears between the targetsurface and the plasma jet during the first discharge, followed by a diffuse plasma plumefrom the target surface towards the plasma jet after the impact of the ionization waveon the target. A hybrid behavior is highlighted for the ultra-pure water which leadsto a short spreading of the ionization wave on the target surface, the formation of aconductive channel in ambient air between tube output and target and the formationof a plasma plume on the target surface.

Features of a negative ionization wave development preceding the full breakdown in a long capillary tube wrapped with a continuous or fine-sectioned grounded electrode

The experimental results on the study of negative ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by high-voltage pulse of negative polarity. The propagation of this surface ionization wave precedes and influences the establishment of complete electric breakdown within the tube. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the general features of a negative ionization wave. The main of them is the tight correlation between local currents determining the formation of local surface charge and visual discharge images taken by the fast camera characterizing the pace of the ionization wave propagation.

Radial current distribution along the ionization wave propagating in a long dielectric capillary tube filled with a low-pressure helium

The experimental results on the study of the ionization wave propagating along a long capillary tube are presented. The ionization wave was initiated by high-voltage pulse of positive or negative polarity. The propagation of this surface ionization wave precedes and influences the establishment of complete electric breakdown within the tube. The spreading of this wave is accompanied by the surface charge deposition. The usage of the fine-sectioned outer electrode allows one to find out the general features of the ionization waves.

Silicon surface assisted laser desorption ionization mass spectrometry for quantitative analysis

The approach to quantitative analysis by silicon Surface Assisted Laser Desorption Ionization Mass Spectrometry (Si-SALDI) is proposed. The approach is based on the new method for forming an active surface layer on a silicon substrate by exposing to laser radiation directly in the ion source of a mass spectrometer. The method can be used repeatedly on the same substrate, providing high reproducibility of its surface ionization properties and high ionization efficiency of organic compounds. Within the proposed approach, the methods of improvement of signal reproducibility are also considered, including continuous monitoring of the silicon surface ionization properties using a Knudsen effusion cell; scanning the surface of a silicon substrate with a laser beam; selecting the optimal value of laser fluence and using a reproducible sample introduction technique. It is demonstrated that this approach can be successfully applied to quantify clinically relevant concentrations of pharmaceutical drugs in extracts of blood.