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Characterization and modeling of a cold atmospheric plasma source for endoscopic treatment

par Bastin, Orianne
Président du jury Reniers, François
Promoteur Delchambre, Alain
Co-Promoteur Nonclercq, Antoine
Publication Non publié, 2022-11-16

Thèse de doctorat

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Résumé :

Cold atmospheric plasma is a partially ionized gas whose electrons exhibit high kinetic energy while ions, atoms and molecules are moderately agitated. It results in a highly reactive medium, at room temperature, containing charged and neutral particles, but also reactive species formed by reaction with molecules or atoms in presence. This reactivity led to the emergence of the plasma medicine field during the last decades, which uses plasma for triggering various effects in living cells, such as proliferation, migration, apoptosis, or necrosis, depending on the plasma dose. With this broad range of effects, developing plasma sources suitable for endoscopic treatment would offer new possibilities for minimally invasive therapies. However, producing a plasma effective at the treatment site (far from its energy source) while preserving the safety of both the patient and the operator represents a technological challenge. This thesis investigates a long Dielectric Barrier Discharge (DBD) plasma jet fitting in an endoscope. It is made of a quartz chamber, connected to a long capillary in Teflon, with a central copper wire (without any electrical connection) that allows for sustaining the plasma over long distances. An electrical equivalent circuit of this plasma endoscopic device was designed, implemented, and assessed. We started with a simpler device version, including the dielectric chamber alone. Model parameters were identified based on the system’s geometry and experimental measurements. On this basis, the whole plasma endoscopic device was modeled and assessed with a similar approach. Both models were positively confronted with experimental measurements. They deepened our understanding of cold atmospheric plasma jets and provided an essential tool for future control of plasma medical devices.Concomitantly, this plasma source was characterized experimentally under two types of excitation: nano-pulsed and sinusoidal high voltages. A comparison was carried out in terms of plasma reactivity and dissipated power. The quartz chamber dimensions were also varied to assess their influence on the system performance. Then, two electrode configurations were compared, and the impact of the target electrical connection was finally studied. This experimental characterization highlighted essential parameters to consider for designing and optimizing future plasma sources for endoscopy, depending on the excitation type.In conclusion, from a fundamental point of view, a plasma endoscopic device model has been designed, implemented, and assessed, providing useful information on internal electrical variables in long plasma jets. From an applicative point of view, the experimental characterization has shown that pulsed plasma is better suited for endoscopy than a sinusoidal one, illustrated the importance of the quartz chamber for design choices, and highlighted the importance of grounding the target. In addition, the model could open the way to real-time monitoring of electrical variables during treatment for safety purposes.