Extraction of Plasma Plume from Atmosphere into Vacuum for Cold Atmospheric Plasma Jet Diagnosis*

A plasma diagnostic method using Langmuir probe has been proposed to determine the plasma parameters of a Cold Atmospheric Plasma (CAP) jet. Placing probes straight into plasma jet results in plasma jet arcing on to probe changing the nature of plasma intended to measure, yielding incorrect results. In our proposed technique, we perform diagnostics by extracting a CAP sample from ambient pressure (1000 mbar) and transferring it to a low pressure (10 mbar) diagnostic chamber where the Langmuir probe is placed. COMSOL simulations were done to determine the size of the system, which can maintain the requisite low pressure even when exposed to ambient atmosphere via an orifice, while keeping the influence of the pressure differential on the velocity of the sampled plasma to a minimum. Based on the modelling results, a system was built, and plasma diagnostic experiments were conducted. Experiments were conducted to determine the effect of probe geometry in the extraction of a glitch-free, and usable IV curve. Based on this, a flat-plate double probe was built and the plasma density, and electron energy distribution were measured from the extracted IV curve using a continuum flowing plasma theory and found to be in good agreement with the earlier reports on jet plasma studies.