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In this study, a two-dimensional axi-symmetric model has been developed in order to shed light into the evolution of a He and He/O2 capillary plasma jet. The plasma jet interacts with a dielectric surface placed normal to the jet axis to bring the model closer to applications. This work examines, from first principles, the shape and speed of the of the plasma bullet, the intensity of the induced electric (IEF) field on the dielectric surface and the underlying dominant chemical reactions of the plasma. Furthermore, the work provides insight and understanding into the mechanisms behind many experimental observations such as the torus (or donut) and sphere plasma bullet shapes for pure Helium and He/O2 plasma, respectively.

Helium DBDs at atmospheric pressure have shown very promising results in many biomedical applications, such as wound healing, treatment of cancer cells, bacterial inactivation etc. In such discharges the presence of water impurities is unavoidable and should be taken into consideration as they affect the plasma composition and plasma dynamics. Water impurities originate from humidity in the ambient air and from the plasma interaction with living tissue typically residing in moist environment. Consequently, understanding the effect of the water admixtures on helium/air discharges is a prerequisite for the utilization of these devices

For the experiments, 4.0 kV, 50 μs duration, 10 kHz pulses are used to excite the plasma discharge through a 20 cm long capillary soda lime glass tube with internal diameter of 0.9 mm. In order to capture the dynamic behaviour of the plasma jet, an Intensified Charged Coupled Device (ICCD) is used. For the simulation model, the gas mixing of the helium with the ambient air is treated through a gas dynamic model that feeds its output to the plasma fluid model [6]. The simulations focus on the effects of the presence of the dielectric target and that of the oxygen admixtures (500ppm-2000ppm) on the plasma bullet shape and speed, the induced electric field, the secondary emission flux of electrons and the dynamic behavior of the chemical reactions (separating also the Penning reaction contributions) responsible for the plasma jet propagation. The numerical and experimental results have good agreement and show that the evolution of the helium plasma jet is highly affected by the introduction of oxygen admixtures.

Atmospheric pressure plasma jets (APPJ) show great potential for biomedical applications. One of the most interesting applications is cancer treatment where APPJ was used effectively in a wide number of different scenarios and in some cases it even exhibited selectivity in treating cancer while leaving the healthy tissue intact. One of the newest developments is plasma enhanced chemotherapy (PEC) where CAP is used synergistically with chemotherapy. PEC promises not only to make chemotherapy more effective (achieving the same results with lower drug doses) but also to enable therapy on resistant cancers. Being able to reduce the drug does and still offer an effective treatment can have significant implications on the patient by limiting the harmful side effects of chemotherapy. In addition, PEC can allow for the treatment of previously untreated cancer.

In this study, a two-dimensional axi-symmetric model has been developed in order to shed light into the evolution of a He and He/O2 capillary plasma jet. The plasma jet interacts with a dielectric surface placed normal to the jet axis to bring the model closer to applications. This work examines, from first principles, the shape and speed of the of the plasma bullet, the intensity of the induced electric (IEF) field on the dielectric surface and the underlying dominant chemical reactions of the plasma. Furthermore, the work provides insight and understanding into the mechanisms behind many experimental observations such as the torus (or donut) and sphere plasma bullet shapes for pure Helium and He/O2 plasma, respectively., International Conference on Phenomena in Ionized Gases (XXXIV ICPIG), July 2019, Sapporo, Japan

Atmospheric pressure plasma jet (APPJ) can be generated in capillary tubes flowing with pure helium and with admixtures of oxygen into the pure helium. The jet exiting the tube can be used for a variety of applications through surface interaction. In this study, a twodimensional axi-symmetric model has been developed to provide insight into the evolution of capillary helium plasma jet with and without the presence of oxygen admixtures and its interaction with a dielectric surface placed normal to the jet axis. The model considers the gas mixing of helium and ambient air and the analytical chemistry between helium, nitrogen and oxygen species. Experiments were performed in similar conditions as the simulations in order to get qualitative agreement between them. The numerical and experimental results show that the evolution of the helium plasma jet is highly affected by the introduction of oxygen admixtures. In particular, it was observed that the addition of oxygen admixtures in the helium gas promotes plasma bullet propagation on the axis of symmetry of the tube (instead off axis propagation for the pure helium plasma jet). On the other hand, the presence of the dielectric surface (the slab placed in front of the tube exit) forces the plasma bullet to spread radially. Furthermore, the plasma bullet speed decreases when the helium plasma jet is operated in the presence of oxygen admixtures. The numerical results also showed that He/O2 plasma jets induced much higher electric fields on the dielectric surface in comparison to the pure helium plasma jet

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ). In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis

Low temperature atmospheric pressure plasma sources have received much attention in the last decades, due to low production cost, easy implementation and applications ranging from surface modification, sterilization, plasma medicine etc. Such plasma sources usually operate with inert gases such as argon, neon or helium, and their electrodes are covered with dielectric layers in order to avoid the transition to arcing. The inert gases are preferred because they create the conditions for lower power requirements and they can produce a wide range of reactive species. However, in several applications, extra admixtures of nitrogen or oxygen species are added in the gases, in order to enhance the production of the reactive species. In the literature, there is a very limited number of studies regarding the effect of these admixtures on the evolution of helium discharge over a wide range. Consequently, understanding the effect of these admixtures (nitrogen and oxygen) on the discharge evolution is very crucial for the utilization of helium atmospheric pressure plasma devices.

Helium DBDs at atmospheric pressure have shown very promising results in many biomedical applications, such as wound healing, treatment of cancer cells, bacterial inactivation etc. In such discharges the presence of water impurities is unavoidable and should be taken into consideration as they affect the plasma composition and plasma dynamics. Water impurities originate from humidity in the ambient air and from the plasma interaction with living tissue typically residing in moist environment. Consequently, understanding the effect of the water admixtures on helium/air discharges is a prerequisite for the utilization of these devices

For the experiments, 4.0 kV, 50 μs duration, 10 kHz pulses are used to excite the plasma discharge through a 20 cm long capillary soda lime glass tube with internal diameter of 0.9 mm. In order to capture the dynamic behaviour of the plasma jet, an Intensified Charged Coupled Device (ICCD) is used. For the simulation model, the gas mixing of the helium with the ambient air is treated through a gas dynamic modelthat feeds its output to the plasma fluid model [6]. The simulations focus on the effects of the presence of the dielectric target and that of the oxygen admixtures (500ppm-2000ppm) on the plasma bullet shape and speed, the induced electric field, the secondary emission flux of electrons and the dynamic behavior of the chemical reactions (separating also the Penning reaction contributions) responsible for the plasma jet propagation. The numerical and experimental results have good agreement and show that the evolution of the helium plasma jet is highly affected by the introduction of oxygen admixtures.

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ). In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis

In the last two decades, the atmospheric pressure plasma jet has gained much attention, due to its low production cost and the wide range of applications such as plasma medicine, local surface modification, local sterilization etc. The plasma jet device has been extensively studied and significant understanding has been gained through analytical/simulation models and experiments. However, deep understanding of the detailed mechanisms of plasma jet evolution and its interaction with material surfaces needs further research. A two dimensional axisymmetric plasma fluid model was used [1], in order to study the evolution and interaction of a capillary helium plasma jet with a dielectric surface. The results of the simulation have been verified with experimental results.

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ). In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis

Atmospheric pressure plasma jets (APPJ) show great potential for biomedical applications. One of the most interesting applications is cancer treatment where APPJ was used effectively in a wide number of different scenarios and in some cases it even exhibited selectivity in treating cancer while leaving the healthy tissue intact. One of the newest developments is plasma enhanced chemotherapy (PEC) where CAP is used synergistically with chemotherapy. PEC promises not only to make chemotherapy more effective (achieving the same results with lower drug doses) but also to enable therapy on resistant cancers. Being able to reduce the drug does and still offer an effective treatment can have significant implications on the patient by limiting the harmful side effects of chemotherapy. In addition, PEC can allow for the treatment of previously untreated cancer.

Atmospheric pressure plasma jets (APPJ) show great potential for biomedical applications. One of the most interesting applications is cancer treatment where APPJ was used effectively in a wide number of different scenarios and in some cases it even exhibited selectivity in treating cancer while leaving the healthy tissue intact. One of the newest developments is plasma enhanced chemotherapy (PEC) where CAP is used synergistically with chemotherapy. PEC promises not only to make chemotherapy more effective (achieving the same results with lower drug doses) but also to enable therapy on resistant cancers. Being able to reduce the drug does and still offer an effective treatment can have significant implications on the patient by limiting the harmful side effects of chemotherapy. In addition, PEC can allow for the treatment of previously untreated cancer.

In the last two decades, the atmospheric pressure plasma jet has gained much attention, due to its low production cost and the wide range of applications such as plasma medicine, local surface modification, local sterilization etc. The plasma jet device has been extensively studied and significant understanding has been gained through analytical/simulation models and experiments. However, deep understanding of the detailed mechanisms of plasma jet evolution and its interaction with material surfaces needs further research. A two dimensional axisymmetric plasma fluid model was used [1], in order to study the evolution and interaction of a capillary helium plasma jet with a dielectric surface. The results of the simulation have been verified with experimental results.

Atmospheric pressure plasma jets are promising for applications in the area of material science and biomedicine. The advantage of the APPJ compared to other atmospheric pressure plasma devices is their ability to deliver in remote locations a wide range of reactive species, charge species, high electric fields and UV photons. Among APPJ devices, helium plasma jets show very encouraging results for biomedical applications where it was observed that a small amount of oxygen in the helium gas increases its effectiveness against cancer cell. Capillaries are of particular interest because they can deliver the plasma jet to previously inaccessible anatomical structures. In this work, the effect of oxygen admixtures on the evolution and interaction of a capillary helium plasma jet device with a dielectric surface is investigated. For the experiments, 4.0 kV, 50 μs duration, 10 kHz pulses are used to excite the plasma discharge through a 20 cm long capillary soda lime glass tube with internal diameter of 0.9 mm. In order to capture the dynamic behaviour of the plasma jet, an Intensified Charged Coupled Device (ICCD) is used. For the simulation model, the gas mixing of the helium with the ambient air is treated through a gas dynamic model that feeds its output to the plasma fluid model [6]. The simulations focus on the effects of the presence of the dielectric target and that of the oxygen admixtures (500ppm-2000ppm) on the plasma bullet shape and speed, the induced electric field, the secondary emission flux of electrons and the dynamic behavior of the chemical reactions (separating also the Penning reaction contributions) responsible for the plasma jet propagation. The numerical and experimental results have good agreement and show that the evolution of the helium plasma jet is highly affected by the introduction of oxygen admixtures.

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ). In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis

Low temperature atmospheric pressure plasma sources have received much attention in the last decades, due to low production cost, easy implementation and applications ranging from surface modification, sterilization, plasma medicine etc. Such plasma sources usually operate with inert gases such as argon, neon or helium, and their electrodes are covered with dielectric layers in order to avoid the transition to arcing. The inert gases are preferred because they create the conditions for lower power requirements and they can produce a wide range of reactive species. However, in several applications, extra admixtures of nitrogen or oxygen species are added in the gases, in order to enhance the production of the reactive species. In the literature, there is a very limited number of studies regarding the effect of these admixtures on the evolution of helium discharge over a wide range. Consequently, understanding the effect of these admixtures (nitrogen and oxygen) on the discharge evolution is very crucial for the utilization of helium atmospheric pressure plasma devices.

Atmospheric pressure plasma jets are promising for applications in the area of material science and biomedicine. The advantage of the APPJ compared to other atmospheric pressure plasma devices is their ability to deliver in remote locations a wide range of reactive species, charge species, high electric fields and UV photons. Among APPJ devices, helium plasma jets show very encouraging results for biomedical applications where it was observed that a small amount of oxygen in the helium gas increases its effectiveness against cancer cell. Capillaries are of particular interest because they can deliver the plasma jet to previously inaccessible anatomical structures. In this work, the effect of oxygen admixtures on the evolution and interaction of a capillary helium plasma jet device with a dielectric surface is investigated.For the experiments, 4.0 kV, 50 μs duration, 10 kHz pulses are used to excite the plasma discharge through a 20 cm long capillary soda lime glass tube with internal diameter of 0.9 mm. In order to capture the dynamic behaviour of the plasma jet, an Intensified Charged Coupled Device (ICCD) is used. For the simulation model, the gas mixing of the helium with the ambient air is treated through a gas dynamic modelthat feeds its output to the plasma fluid model [6]. The simulations focus on the effects of the presence of the dielectric target and that of the oxygen admixtures (500ppm-2000ppm) on the plasma bullet shape and speed, the induced electric field, the secondary emission flux of electrons and the dynamic behavior of the chemical reactions (separating also the Penning reaction contributions) responsible for the plasma jet propagation. The numerical and experimental results have good agreement and show that the evolution of the helium plasma jet is highly affected by the introduction of oxygen admixtures.

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ) [1]. In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer [2]. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells [3]. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis. In this abstract a two-dimensional axi-symmetric model is developed [4] for the description of a capillary helium plasma jet with and without the presence of oxygen admixtures and their interaction with a dielectric surface placed normal to the jet axis. The results in Figure 1 show that He/O2 plasma jets generates higher IEF in comparison to the pure He plasma jet. Furthermore, the peak of the IEF on the dielectric surface is on the axis of symmetry for He/O2 plasma jets and off the axis of symmetry for pure He plasma jet. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under agreement No. 810686. References [1] D. B. Graves, Phys. Plasmas, 21, 080901 (2014) [2] J. Van der Paal, C. Verheyen, E. C. Neyts and A. Bogaerts, Sci. Rep., 7, 39526 (2017) [3] S. J. Kim, T. H. Chung, S. H. Bae and S. H. Leem, Appl. Phys. Lett., 97, 023702 (2010) [4] C. Lazarou, C. Anastassiou, I. Topala, A. S. Chiper, I. Mihaila, V. Pohoata and G. E. Georghiou, Plasma Sources Sci. Technol., 27, 105007 (2018), International Workshop on Plasma for Cancer Treatment (IWPCT 2019), April 1-3, 2019 Antwerp, Belgium

Reactive oxygen and nitrogen species (RONS) play a central role in the immune system and on disease progression and therefore are important in the therapeutic abilities of the atmospheric pressure plasma jet (APPJ). In addition to RONS, the APPJ induces an electric field (IEF) on the biological cells. It can be inferred that it is the combination of IEF and RONS and not just RONS that gives the APPJ its unique therapeutic abilities, such as selectively treating cancer. In the case of helium APPJ it was found that the addition of oxygen impurities allowed for more effective treatment of cancer cells. Putting it all together, the hypothesis is that the addition of oxygen causes higher IEF on cancerous cells causing electroporation and the introduction of RONS in the cells causing apoptosis