Mancini, Davide (2019) Development and characterization of an atmospheric plasma source for non-thermal blood coagulation. [Magistrali biennali]
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In this thesis is developed and charachterized Plasma Coagulation Controller (PCC): a cold atmospheric plasma source designed for acceleration of non thermal blood coagulation. PCC is based on the Dielectric Barrier Discharge (DBD), it ionizes a neutral gas through the application of a fast voltage pulse to an electrode covered in dielectric material. Electrical charachterization of the prototype developed in this work allows to observe voltage pulses with amplitude up to 10 kV while current intensity is always lower than 10 mA, for repetition rates from 1 to 40 kHz. A peculiar phenomenon in DBD sources is that plasma propagates producing bullets: localized zone of plasma expelled at velocities higher than 10 km/s. In this work plasma bullets are observed with a fast frame acquisition setup that allows to observe the discharge with an integration time of 15 ns. The principal analysis revolves around production and propagation of plasma bullets with different experimental setups such as: voltage pulse amplitude, composition of neutral gas (chosen between helium, neon and argon) or typology of the target placed in front of the source (e.g. insulating or conductive targets). The comparision of bullets produced with helium and neon gas suggests that bullet propagation velocity is related to electron mobility. The measurements of current intensity in a conductive target allows to observe that current flows in the target before impact with the bullet. Bullets are not observed using argon, with this gas plasma dynamics is characterized by the production of filaments that differs from bullets. Emission spectroscopy analysis is performed assuring the presence of OH, N 2 and N 2 + molecules, with different intensities for different operational regimes. The relative emission of gas components is studied for different plasma positions and gas composition, finding that during plasma propagation in air emission is always dominated by nitrogen transitions. Temperature increase due to plasma application on an inorganic target is measured with a thermal camera. Power deposition of a single voltage pulse is found to be inversely proportional to pulse repetition rate and to target distance, while it increases with higher voltage peaks.
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