O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

The doctoral thesis deals with the experimental study of the low-temperature plasma designated for the preparation of thin films using the method of physical sputtering. It describes measurements which were realized on two types of devices - on the low-pressure plasma jet sputtering system and on the planar magnetron. The plasma diagnostics in the discharge excited in the pulse regime represent the main theme of the thesis. The discharge in the low-pressure plasma jet was studied by means of an electrostatic Langmuir probe, in the case of the planar magnetron, mass spectroscopy with energetic as well as time resolution was used. To understand the results achieved in the pulse generated plasma good knowledge of the basic continuous DC regime of the discharge excitation is essential. Therefore a considerable part of the thesis deals purely with the continuous DC discharge. In the case of the low- pressure plasma jet, the attention was focused also on the characteristic property of this plasma source, which is the flow from the jet.

O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

Submitted by ALONSO HERNAN RICCI CASTRO null (alonso_elfisico@yahoo.com) on 2017-08-17T17:22:54Z No. of bitstreams: 1 Castro_AHR_PHD.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-08-23T17:50:32Z (GMT) No. of bitstreams: 1 castro_ahr_dr_guara.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) / Made available in DSpace on 2017-08-23T17:50:32Z (GMT). No. of bitstreams: 1 castro_ahr_dr_guara.pdf: 57242725 bytes, checksum: 36378feb1c1464a31ab9ed5824539173 (MD5) Previous issue date: 2017-06-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho teve como objetivo o estudo dos parâmetros que influenciam o comportamento de um jato de plasma em pressão atmosférica e sua aplicação em deposição de filmes poliméricos. Com esta finalidade, foram utilizadas duas diferentes configurações de eletrodos em jatos de argônio: um de eletrodo anular externo e outro com eletrodo cilíndrico interno. Também foram utilizadas três geometrias diferentes de bocal de saída do jato (cônico fechado, reto e cônico aberto), usando um eletrodo cilíndrico interno. Os jatos de plasma de argônio operam em modo filamentar, com os filamentos se espalhando por todo o volume do tubo dielétrico, disposto coaxialmente ao eletrodo. Neste trabalho também foi desenvolvido um jato de plasma para a deposição de filmes poliméricos, constituído de um eletrodo de alta tensão em forma cilíndrica localizado no eixo longitudinal do jato, e um eletrodo aterrado na forma de anel que está fixado ao redor do bocal do jato. O estudo foi iniciado com a comparação de dois métodos utilizados para o cálculo da potência. Para os dois jatos de plasma observou-se que o método mais adequado para calcular a potência de descarga é o método da figura de Lissajous, que fornece um erro experimental menor que 3 %. Após realizar a caraterização elétrica dos jatos de plasma, pode-se observar que a potência e a forma de onda da corrente dependem de diferentes parâmetros, que são apresentados em ordem da maior a menor influência da distância bocal-substrato, do fluxo de gás, do tipo de substrato e da geometria do bocal. A deposição de filmes poliméricos foi influenciada pela geometria do jato de plasma e do fluxo dos gases. Os filmes depositados sem movimento do substrato apresentam uma taxa de deposição de 1 m/min. A análise XPS mostrou que os filmes são constituídos em sua maioria por grupos alifáticos C-C/C-H e em menor proporção por hidroxila, éster e ácido carboxílico. Mediante a implementação de uma plataforma móvel foi possível depositar filmes poliméricos em uma grande área, o que amplia a gama de aplicações dos jatos de plasma desenvolvidos neste trabalho. / The goal of this work was to study the parameters which influence the electrical behavior of a atmospheric pressure plasma jet and its application for polymeric films deposition. For this purpose, two different configurations of electrodes were used in argon jets: one with an external annular electrode and the other with an internal cylindrical electrode. Also, three different jet nozzle geometries were adopted using an internal cylindrical electrode: tapered nozzle, straight nozzle and enlarged nozzle. The argon plasma jets operate in filament mode, with the filaments spreading throughout the volume of the dielectric tube, arranged coaxially to the electrode. On this work, a plasma jet system was developed to deposit polymer films, this system consists of a cylindrical high voltage electrode located in the longitudinal axis of the jet, and a grounded electrode in the form of a ring that is fixed around the nozzle of the jet. The study started comparing both methods for calculation of the power of plasma jets. Afterwards, it was concluded that the best method was the Lissajous method giving 3 % of experimental error. After electrical characterization of the plasma jet it was found that the power and current were influenced by different parameters, presented in order of their importance: distance, gas flow, type of substrate and nozzle geometry. The polymer films deposition was influenced by the plasma jet geometry and the gas flow. The films deposited without movement have 1 m/min of deposition rate. The XPS analysis shows that the films are made mostly from aliphatic groups C-C/C-H and in lesser extension by hydroxyl, ester and carboxylic acid. Through implementation of mobile platform was possible to deposit polymer films over larger area.

O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

When entering a planet’s atmosphere, spacecraft induce a strong compression shock and must be protected from the resulting extreme heat flux by a thermal protection system made of either reusable or ablative materials. To characterise these materials, the harsh flow conditions of atmospheric entry are reproduced in plasma wind tunnels, where a jet of gas heated up to ionisation is directed at material samples for prolonged testing. Unfortunately, heated jets exhibit complex dynamic behaviours, resulting in oscillations that increase the uncertainties in the experiments.At sufficient Reynolds numbers, the dynamic behaviour of heated jets shifts from an amplifier to a self-sustained oscillator type via a Hopf bifurcation, if the centreline-to-ambient density ratio falls below a given threshold. This change is known in the literature to be related to the onset of absolute instabilities in the flow. However, this type of instability is usually studied for a simplified description of the gas, which is not suitable for the case of a plasma wind tunnel.This doctoral work investigates the nature of the instabilities responsible for the oscillations observed in a plasma jet, similar to the one in the VKI Plasmatron facility. The analysis is carried out by comparing results from different numerical methods, including linear stability analyses (both local and global) and direct numerical simulations. The thesis first describes the effect of high-temperature gas models on the stability of synthetic jets found in the literature, before analysing the case of Plasmatron.The analysis of synthetic jets with real-gas effects shows that the onset of the first dissociation reactions in the flow has a strong influence on the prevailing type of instability. Furthermore, if a sufficiently long region of absolute instability is present in the jet, the flow bifurcates to a periodic limit cycle, and steady state solutions become inadequate to describe the flow and its dynamic behaviour. In this case, a stability analysis of the time-averaged state can accurately reproduce the results of direct numerical simulations. In the case of Plasmatron, a large region of absolute instability is revealed in the plasma jet, suggesting that the observed oscillations are caused (in part) by a global non-linear mode and that the flow has entered a limit cycle. Trends of the absolute instability frequency with respect to the driving parameters of Plasmatron are in agreement with experimental observations.The present work confirms that global stability features of heated jet flows are very sensitive to subtle changes of the undisturbed or time-averaged state, which results from technological constraints in the case of Plasmatron. Furthermore, this thesis has shown the relevance of including high-temperature gas effects in the stability analysis of high-enthalpy jets. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Dans cette thèse de doctorat, des simulations numériques basées sur un modèle fluide 2D sont utilisées pour caractériser des jets de plasma d’Hélium pulsés. Le modèle pour les jets de plasma d’Hélium est développé pour décrire des jets qui s’écoulent dans des atmosphères de N2 et O2 et interagissent avec des cibles. La dynamique de la décharge dans les jets d’Hélium impactant une cible métallique à la masse est analysée pour des polarités positive et négative de la tension appliquée. Les évolutions temporelles et spatiales de champ électrique associées au premier front d’ionisation et au front de rebond sont en bon accord qualitatif avec des mesures récentes de champ électrique. Puis, l’interaction plasma cible entre une décharge positive et une cible diélectrique en BSO est examinée en détail et les résultats sont directement comparés aux expériences. Un bon accord est obtenu entre les simulations et les expériences sur les évolutions temporelles et spatiales de champ électrique. Des valeurs maximales de champ électrique dans la cible de 5 kV.cm−1 ont été obtenues expérimentalement et numériquement. Le champ électrique dans le plasma de l’ordre de quelques dizaines de kV.cm−1 est fortement diminué par le changement de permittivité de la cible. Le champ électrique dans la cible est presque exclusivement dû aux fortes valeurs de charges de surface déposées sur la surface de la cible. Finalement, l’influence des évolutions de champ électrique sur la production d’espèces actives près des cibles est évaluée. On démontre qu’avec des cibles métalliques la synergie entre le premier front et le front de rebond augmente la production d’espèces près de la cible. / In this PhD thesis numerical simulations based on a 2D fluid model are used to characterize pulsed Helium plasma jets. The model for He plasma jets is developed to describe He jets flowing in N2 and O2 atmospheres and interacting with targets. The discharge dynamics in He jets impacting a grounded metallic target is analyzed with both positive and negative polarities of applied voltage. The temporal and spatial evolutions of electric field associated to the first and rebound ionization fronts are in good qualitative agreement with recent electric field measurements. Then, the plasma-target interaction occurring between a positive discharge and a BSO dielectric target is investigated in detail and results are directly compared with experiments. A good agreement is obtained between simulations and experiments concerning the temporal and spatial profiles of electric field. Maximum values of electric field inside the target of 5 kV.cm−1 are found. The high electric field in the plasma of the order of dozens of kV.cm−1 is severely depleted by the change of permittivity. As a result, the electric field experienced inside the target is almost exclusively originated by the high values of surface charge deposited on the target surface. Finally, the influence of the electric field evolutions on the production of chemically active species close to the targets is evaluated. It is shown that with metallic targets the synergy between the first and rebound fronts increases species production close to the target.

Ces dernières années un nouveau type de décharges hors équilibre thermodynamique, aptes à générer des micro jets de plasma se propageant en atmosphère libre, a suscité beaucoup d’intérêt dans la communauté scientifique. Ces micro jets, produits dans des structures type décharge à barrière diélectrique, ont des propriétés particulièrement intéressantes, tant sur le plan de la physique des plasmas que sur celui des applications, en particulier pour des applications biomédicales ou de traitement de surface.Dans ce travail de thèse il est démontré que ces jets de plasma correspondent à la propagation à grande vitesse d'un front d'ionisation sans déplacement de matière. Une caractérisation des propriétés des jets (vitesse et distance de propagation) a été effectuée en fonction de la tension appliquée, du débit, de la composition du gaz, et de la géométrie de la décharge. La distribution spatio-temporelle des espèces réactives produites par le jet a été mesurée, et en particulier celle de l'état métastable He (2³S) mesuré par absorption laser. Des densités comprises entre 1.10¹² et 5.10¹³ cm-³ ont été obtenues pour l’état He (2³S). Sa distribution est annulaire à la sortie de la structure de la décharge et se referme le long du jet. La densité maximale est obtenue à une distance correspondant à la moitié de la zone où les atomes métastables sont présents, ce qui est en contradiction avec les modèles actuels. De plus, afin de mieux comprendre la physique des jets de plasma, nous avons fait interagir deux jets placés l’un en face de l’autre. L'étude de la contre propagation de deux jets révèle qu’il existe une distance minimale d'approche laissant entre eux une zone exempte de plasma. Après l’extinction des deux plasmas, une seconde décharge s’amorce exactement dans cette zone. Une étude détaillée couplant diagnostics électrique, imagerie ultra-rapide et spectroscopie d'émission nous a permis de montrer que cette décharge secondaire est due à une inversion de polarité conduisant à la création transitoire d'un piège à électrons.Dans le but d'aborder l'étude des applications des jets de plasma au domaine biologique, nous avons également étudié la dégradation de l’ADN plasmidique par un jet de plasma. Nous avons mis en évidence que ce type de plasma induit majoritairement des cassures simples et doubles brins, alors que très peu d’oxydations de base ou de sites abasiques sont observés, ceci même avec l’ajout de quelques pourcents d’oxygène dans le gaz. / Micro plasma jets operating at atmospheric pressure in free atmosphere have recently attracted great attention because of their numerous advantages. In fact, micro plasma jets can be operated stably at atmospheric pressure and propagated over some centimeters in a free atmosphere. Moreover, these jets are non-thermal plasmas and create numerous reactive species. These properties allow to use this kind of plasma in many applications, such as surface treatment, decontamination, and plasma medicine.In this work it is shown that these micro plasma jets correspond to the fast propagation of an ionization front with no displacement of matter. A characterization of the plasma proprieties (e.g. distance and velocity of propagation) has been done as a function of the applied voltage, gas flow, gas composition and discharge geometry. The spatiotemporal distribution of the reactive species created by the plasma has been measured, with a special focus on the helium metastable atoms which have been measured by absorption laser spectroscopy. The helium metastable atom densities obtained are in the range of 1.10¹² to 5.10¹³ cm-³. Thanks to a very good spatiotemporal resolution, we have done a time-resolved full cartography of the plasma. This allowed us to show that the helium metastable atom distribution is annular near the nozzle and becomes circular as the plasma propagates. The maximum helium metastable atoms density has been measured at about half of the distance where the helium metastable atoms are present. This observation is in contradiction with results reported by numerical models. To gain further insight into the physical processes of the plasma, we have placed two micro plasma jets face to face. This study showed that both plasmas interact in such a way that they never come into contact, letting a space free of plasma between them. Moreover, we revealed that after the extinction of the plasmas, a second discharge is ignited in the previously free space. Fast imaging, spectroscopy diagnostics and electrical measurements showed that this second discharge is due to a polarity reversal, which creates an electron trap. Aiming the study of the application of micro plasma jets in the plasma medicine field, we have studied the degradation of plasmid DNA by our plasma jet. We observed that the plasma treatment leads mostly to single and double strands breaks, and to very little base oxidation and abasite site, even when oxygen is added into the gas mixture.

This thesis presents an experimental study of non-thermal atmospheric pressure gas plasmas in presence of liquid as an efficient source of transient and reactive species to initiate chemical reactions necessary for many important applications. Two types of liquid-containing plasmas are considered: discharges formed between a needle electrode and a liquid electrode, and plasma jets formed in a water vapour flow mixed in helium or argon gas. Two plasma modes (the pulsed and the continuous mode) are observed in the needle-to-liquid plasma. A comparative study of the needle-to-liquid plasma in the continuous mode with DC and AC excitations reveals that the plasmas are glow discharges, and AC excited plasmas have the highest energy efficiency. A study of helium/water vapour plasma jet shows that “plasma bullets” are formed even with water vapour in the gas mixture, but become quenched when the moist helium flow rate is above 300sccm (~1800ppm water concentration). Moderate amount of water vapour (~250ppm water concentration) is beneficial for active species production mainly due to the high electron density. Hydrogen peroxide production in saline solution with three different plasma sources is investigated due to the importance of H2O2 in several important applications. Long lifetime of H2O2 in the liquid after plasma treatment indicates an exciting possibility of plasma pharmacy.

No presente estudo, um conjunto de três experimentos foram conduzidos com o objetivo de avaliar a ocorrência de Staphylococcus aureus e Listeria monocytogenes em três lacticínios (A, B e C) localizados na região sudeste do Brasil de dezembro 2013 a abril de 2015 (Experimento 1), a eficiência do tratamento com ácido peracético (APA) e jato de plasma a frio (PF) para inativar os isolados em diferentes tempos (Experimento 2) e a capacidade dos isolados produzir biofilmes na superfície de poliestireno e de aço inoxidável, juntamente com inativação e remoção de células aderidas pelo APA (Experimento 3). No Experimento 1, foram analisadas amostras de leite e queijo, superfícies com e sem contato com alimentos. L. monocytogenes foi isolada em apenas uma amostra (0,3%, N = 349) de ralo no laticínio B, enquanto seis (1,7%, n = 349) S. aureus foram isolados de luvas de manipuladores em laticínio A, salmoura no laticínio B e superfície do queijo, utensílio, bota e mão esquerda de trabalhador no lacticínio C. Apesar das incidências desses dois agentes patogênicos de origem alimentar nos lacticínios avaliados foram baixo, sua presença também indica a necessidade de controle estratégias para impedir a sua persistência e contaminação cruzada. No Experimento 2, tratamento com APA (0,5%) e jato de PF foram aplicados diretamente sobre suspensões de isolados de S. aureus e L. monocytogenes. A inativação bacteriana (aproximadamente de 7 ciclos log) foi alcançada em 120 seg. com o tratamento com APA para todos os isolados, enquanto que o tratamento com plasma a frio reduziu aproximadamente 2 ciclos log nas superficies. Outros estudos usando tratamentos de plasma a frio mais longos são necessários para a total descrição da cinética desta tecnologia para a inativação de importantes patógenos de origem alimentar. No Experimento 3, o tratamento com APA (0,5%) em diferentes tempos (0-controle, 15, 30, 60 e 120 seg.) foi avaliada para a remoção de células aderidas de quatro isolados de S. aureus e um isolado de L. monocytogenes em microplacas de poliestireno, assim como para a inativação de biofilmes dos isolados em aço inoxidável. O tratamento com APA removeu (p<0,05) células aderidas de todos os isoladoas estudados S. aureus da superfície, sem diferenças (p> 0,05) no indice de formação de biofilmes nos tempos de tratamento. No entanto, nenhum efeito (p> 0,05) foi observado em células aderidas de L. monocytogenes. A microscopia de epifluorescência mostrou que todas as bactérias testadas foram parcialmente e completamente inativadas após 15 seg e 30 seg. respectivamente. Os resultados indicam um potencial para a utilização de APA contra biofilmes formados por S. aureus e L. monocytogenes, e da necessidade de novos estudos com a PF para determinar os parâmetros ideais para a inativação dos patógenos de origem alimentar. / In the present study, a set of three experiments were conducted aiming to evaluate the occurrence of Staphylococcus aureus and Listeria monocytogenes in three dairy plants (A, B and C) from Southeast region of Brazil from December 2013 to April 2015 (Experiment 1), the efficiency of peracetic acid (PAA) and cold plasma (CP) jet treatment to inactivate the isolates at different times (Experiment 2) and the ability of the isolates to produce biofilms on polystyrene and stainless steel surface, along with inactivation and removal of biofilms by PAA (Experiment 3). In Experiment1, samples of milk and cheese, food contact surfaces and non-food contact were analyzed. L. monocytogenes was isolated in only one sample (0.3%, N=349) of drain sponge swab in dairy plant B, while 6 (1.7%, N=349) S. aureus strains were isolated from handlers\' glove in dairy plant A, brine in dairy plant B and cheese surface, cheese utensil, worker\'s boot and worker\'s left hand in dairy plant C. Although the incidences of those two food-borne pathogens in the dairy plants evaluated were low, their presence also indicates the need for control strategies to prevent their persistence and cross-contamination. In Experiment 2, PAA (0.5%) and CP jet treatment were applied directly on suspensions of S. aureus and L. monocytogenes strains. Reduction of bacterial load (nearly 7 log cycles) was achieved with 15 sec. of PAA treatment of all strains, whereas CP treatment reduced approximately 2 log cycles after 2 min. Hence, plasma treatment has a potential for reducing the bacterial load on surfaces, although further studies using longer CP treatment times are necessary to fully describe the kinetics of this technology for inactivation of important food pathogens. In Experiment 3, PAA (0.5%) treatment at different times (0-control, 15, 30, 60 and 120 sec.) was evaluated for removing of adherent cells of 4 strains of S. aureus and one strain of L. monocytogenes on polystyrene plates, as well as for inactivation of biofilms of those strains on stainless steel. PAA treatment removed (p<0.05) all the S. aureus cells from the surface, with no difference (p>0.05) in the reduction of the biofilm-forming index at the treatment times. However, no effect (p>0.05) was observed on L. monocytogenes adhered cells. Epifluorescence microscopy showed that all bacterial strains tested were partially and completely inactivated after 15 sec. and 30 sec., respectively. Results indicate a potential use of PAA against biofilms formed by S. aureus and L. monocytogenes, and the need of further studies with CP to determinate the ideal parameters for inactivation of food-borne pathogens.