The present work is devoted to the precise spatiotemporal mapping of the absolute density of Ar(1s5) in a ns‐pulsed argon plasma jet. The plasma impinges on glass and alumina targets at floating potential placed 5 mm away from the reactor's nozzle. Under these conditions, diffuse discharges are established in the small gas gap. As so, the line‐of‐sight absolute density of Ar(1s5) is effectively evaluated via laser absorption spectroscopy. The application of the Abel‐inversion is also demonstrated for different operating conditions leading to the precise radial mapping of the Ar(1s5) absolute density. The influence of each target is studied for two gas flow rates, 0.3 and 0.4 l min−1. The temporal density profiles over a voltage pulse period reveal two maxima related with the Ar(1s5) production in the streamer head and in the residual diffuse plasma channel. Furthermore, the maximum Ar(1s5) axial/radial density (∼1013 − 3.5 × 1014 cm−3) depends on the target material and gas flow rate. Finally, the plasma is proved to be very effective for the fast desorption of organic molecules (bibenzyl) deposited on both targets. The results obtained suggest that the desorption of bibenzyl is due to the production of high Ar(1s5) densities at the close vicinity of the targets.
A coaxial configuration of discharge is proposed for plasma surface treatment and possibly other applications. The reactor is based on a cylindrical structure, with the inner cylinder radio frequency powered (RF, 13.56 MHz) and the outer cylinder grounded, playing the role of a guard ring. The charged species can escape from the inner cavity through two longitudinal slits made in both cylinders, aligned to each other, and producing a linear slab of plasma. Hence, it is possible to project the plasma directly onto a surface placed under the slits, called external plate. The operation of this device is uniform and stable in argon for a large pressure range (0.8-50 mbar). Furthermore, simulations using the Plasimo™ software package were performed to evaluate the plasma parameters and to explain the experimental results. The ion flux on the surface exposed to this plasma increases when RF power increases, and the pressure or gap distance to the plate decreases. This cylindrical capacitive coupled plasma configuration can be very effective for surface treatment of different materials (conductors or insulators) on large area (when the plate or the system is moving perpendicular to the slits) due to energetic ions and active species released from the plasma.
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