Langmuir Probe Diagnosis of a Cold Atmospheric Plasma Jet

Langmuir probe characterization of cold atmospheric plasma (CAP) jet requires placing the probe directly in the downstream region, which generates additional filament discharges and alters the plasma characteristics. Also, the large sheath thickness compared to the low mean free path at atmospheric pressure and large plasma flow velocity forbids the use of conventional collisionless stationary plasma theory for probe analysis. In this work, a system has been envisaged to sample the CAP jet into a low-pressure chamber using an orifice for Langmuir probe-based plasma diagnostics. Simulations were performed to ascertain the possibility of generating and maintaining a low pressure inside such an open chamber, while the increase in gas velocity can be kept at a minimum value. Based on the simulation results, a chamber was fabricated and the results were verified experimentally. A Langmuir probe based on a double probe configuration was developed to acquire the I-V curve from the sampled plasma. The effects of sheath collisions, fluid velocity, and pressure differential were accommodated in the probe analysis to calculate the electron temperature and ion number density.