Plasma Microjets at Atmospheric Pressure – PAMPA

The PAMPA project focuses on the study of non-thermal, atmospheric-pressure plasma "microjets" and possible application in two areas with high societal impact: biomedical and wall cleaning of the ITER castellation. Activities in France in the area of plasma microjets are relatively modest in size and unstructured in comparison to activities in other countries where large programs are being put in place. The expertise in France in this area is high, so that the French community could play a leading role in the development of plasma microjets if an ambitious project is funded. Our focus in the proposed project is understanding the physics of plasma microjets which is presently unknown, developing an expertise in France in this area, and evaluating their potential for technical application, in particular for the two areas, biomedical and wall cleaning of ITER, of high societal impacts.
The PAMPA program has been divided into three separate parts, and five different tasks (including a coordination task). Modelling, fast imaging techniques and time resolved spectroscopy will be the tools extensively used in the four technical tasks.
1) Set-up, diagnostics and models of the main discharge (task #2)
With only one exception, the literature indicates that the microjet generation is preceded by the breakdown of main discharge. Thus, in the first step of the PAMPA project, it is of primary importance to identify the physical parameters responsible for the creation of the microjets, and to determine if all the microjets are due to the same processes. To do that GREMI will be more specifically in charge of the development of fast imaging diagnostics to study the spatio-temporal development of the discharge (task # 3), while LPGP and LSP will mainly concentrate on time-resolved spectroscopic investigations (task # 4) in order to get information on the plasma parameters (electron density and temperature, density of excited states, gas temperature …). LAPLACE is in charge of modelling activities and of the development of an RF excited microjet.
2) Development, propagation (task #3), and plasma properties of microjets (task #4).
There is not yet a good understanding of the mechanisms leading to the formation of the microjets in different discharge conditions. One interesting phenomenon, not at all understood, is the generation of plasma "bullets" in certain conditions of pulsed excitation. While a simple model based on the idea of positive streamers propagating towards a virtual ground plane has been proposed, much experimental and theoretical work remains to be done to validate this approach. The development of fast imaging technique and the analysis of the jet propagation will be the goal of task #3, while the spectroscopic analysis will be the goal of task #4. Another issue concerning the microjet physics is the role of the mixing between the carrier gas and ambient atmosphere. The concern here is gas flow, gas mixing, and energy transfer from rare gas metastable atoms to reactive oxygen or nitrogen species. Moreover the stability of the jet (an important issue for applications) and the propagation distance also depend on this parameter. The LAPLACE team will develop a numerical model for the solution of Navier-Stokes equations in a 2D cylindrical geometry and the model predictions will be compared to the experimental results.
3) Applications of plasma microjets in emerging fields (task #5).
While the main motivation of the PAMPA project is to achieve a significant enhancement of the physical understanding of plasma jets production and propagation, the usefulness of plasma microjets for some specific applications will be investigated. We selected specifically two areas, the biomedical and ITER wall castellation, which are important application areas of great potential benefit to society and for which the use of non-thermal plasma tools allowing localized surface treatment seems especially appealing.