6 results
Search Results
Now showing 1 - 6 of 6
- ItemPhase-resolved measurement of electric charge deposited by an atmospheric pressure plasma jet on a dielectric surface(Bristol : Institute of Physics Publishing, 2014) Wild, R.; Gerling, T.; Bussiahn, R.; Weltmann, K.-D.; Stollenwerk, L.The surface charge distribution deposited by the effluent of a dielectric barrier discharge driven atmospheric pressure plasma jet on a dielectric surface has been studied. For the first time, the deposition of charge was observed phase resolved. It takes place in either one or two events in each half cycle of the driving voltage. The charge transfer could also be detected in the electrode current of the jet. The periodic change of surface charge polarity has been found to correspond well with the appearance of ionized channels left behind by guided streamers (bullets) that have been identified in similar experimental situations. The distribution of negative surface charge turned out to be significantly broader than for positive charge. With increasing distance of the jet nozzle from the target surface, the charge transfer decreases until finally the effluent loses contact and the charge transfer stops.
- ItemModeling of Atmospheric-Pressure Dielectric Barrier Discharges in Argon with Small Admixtures of Tetramethylsilane(Dordrecht : Springer Science + Business Media B.V., 2021) Loffhagen, Detlef; Becker, Markus M.; Czerny, Andreas K.; Klages, Claus-PeterA time-dependent, spatially one-dimensional fluid-Poisson model is applied to analyze the impact of small amounts of tetramethylsilane (TMS) as precursor on the discharge characteristics of an atmospheric-pressure dielectric barrier discharge (DBD) in argon. Based on an established reaction kinetics for argon, it includes a plasma chemistry for TMS, which is validated by measurements of the ignition voltage at the frequency f=86.2kHz for TMS amounts of up to 200 ppm. Details of both a reduced Ar-TMS reaction kinetics scheme and an extended plasma-chemistry model involving about 60 species and 580 reactions related to TMS are given. It is found that good agreement between measured and calculated data can be obtained, when assuming that 25% of the reactions of TMS with excited argon atoms with a rate coefficient of 3.0×10−16m3/s lead to the production of electrons due to Penning ionization. Modeling results for an applied voltage Ua,0=4kV show that TMS is depleted during the residence time of the plasma in the DBD, where the percentage consumption of TMS decreases with increasing TMS fraction because only a finite number of excited argon species is available to dissociate and/or ionize the precursor via energy transfer. Main species resulting from that TMS depletion are presented and discussed. In particular, the analysis clearly indicates that trimethylsilyl cations can be considered to be mainly responsible for the film formation.
- ItemTreatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet(College Park, MD : Institute of Physics Publishing, 2010) Koban, I.; Matthes, R.; Hübner, N.-O.; Welk, A.; Meisel, P.; Holtfreter, B.; Sietmann, R.; Kindel, E.; Weltmann, K.-D.; Kramer, A.; Kocher, T.Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% Chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log 10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemMechanisms of low-frequency dielectric barrier discharge (DBD) plasma driven by unipolar pulses and bipolar pulses(New York, NY : American Inst. of Physics, 2021) Truong, Hoa Thi; Uesugi, Yoshihiko; Nguyen, Xuan BaoIn this study, experimental results presenting the development of Dielectric Barrier Discharge (DBD) powered by bipolar and unipolar pulses are compared. The experimental results showed that discharge current peaks in the case of DBD driven by repetitive unipolar pulses were about three times lower than those in the case of DBD driven by bipolar pulses. It is well known that if DBD is driven by bipolar pulses, the effect of surface charge on dielectric layers from the preceding discharge helps to ignite consecutive discharges at the same locations where the previous discharges already struck. In contrast, in the case of DBD generated by using the low-frequency unipolar pulses, the consecutive DBDs just could be initiated after the system erases part of the prehistory effect of surface charge deposition on dielectric layers from the preceding discharge, and then the following discharge was ignited at erased or uncharged areas. It was critical that a part of the energy stored in the dielectric layer and discharge gap by the previous discharge needed to be released to develop the next discharge. The results of this study provided an outlook for estimating the effectiveness of the DBD plasma system used in specific applications such as DBD for flow actuators or surface treatment where the use of unipolar DBDs at low frequency may be necessary.
- ItemExploring the mechanisms leading to diffuse and filamentary modes in dielectric barrier discharges in N 2 with N 2 O admixtures(Berlin ; Heidelberg : Springer, 2023) Höft, Hans; Becker, Markus M.; Kettlitz, Manfred; Dap, Simon; Naudé, Nicolas; Brandenburg, Ronny; Weltmann, Klaus-DieterAbstract: The effects of nitrous oxide (N2O) in nitrogen (N2) on the development and morphology of sine-driven dielectric barrier discharges in a single-filament arrangement were studied. Detailed insight in the characteristics of the discharge and its development were obtained from electrical measurements combined with ICCD and streak camera recordings as well as numerical modelling. A miniaturised atmospheric pressure Townsend discharge (APTD) could be generated for admixtures up to 5 vol% N2O in N2 although N2O is an efficient collisional quencher of metastable nitrogen molecules. Increasing the high voltage amplitude led to a transition into a hybrid mode with the generation of an intermediate filament in addition to the diffuse, non-constricted APTD. A time-dependent, spatially one-dimensional fluid model was applied in order to study the underlying mechanisms causing the diffuse discharge characteristics. It was found that even for small N2O admixtures, the associative ionisation of atomic nitrogen and oxygen (O + N(2P) → NO+ + e) is the major electron source sustaining the volume memory effect and is therefore the reason for the formation of a diffuse APTD. Graphical abstract: [Figure not available: see fulltext.].
- ItemNumerical investigation on the dynamics and evolution mechanisms of multiple-current-pulse behavior in homogeneous helium dielectric-barrier discharges at atmospheric pressure(New York, NY : American Inst. of Physics, 2018) Zhang, Yuhui; Ning, Wenjun; Dai, DongA systematic investigation on the dynamics and evolution mechanisms of multiple-current-pulse (MCP) behavior in homogeneous dielectric barrier discharge (HDBD) is carried out via fluid modelling. Inspecting the simulation results, two typical discharge regimes, namely the MCP-Townsend regime and MCP-glow regime, are found prevailing in MCP discharges, each with distinctive electrical and dynamic properties. Moreover, the evolution of MCP behavior with external parameters altering are illustrated and explicitly discussed. It is revealed that the discharge undergoes some different stages as external parameters vary, and the discharge in each stage follows a series of distinctive pattern in morphological characteristics and evolution trends. Among those stages, the pulse number per half cycle is perceived to observe non-monotonic variations with applied voltage amplitude (Vam) and gap width (dg) increasing, and a merging effect among pulses, mainly induced by the enhanced contribution of sinusoidal component to the total current, is considered responsible for such phenomenon. The variation of incipient discharge peak phase (Φpm) is dominated by the value of Vam as well as the proportion of total applied voltage that drops across the gas gap. Moreover, an abnormal, dramatic elevation in Jpm with dg increasing is observed, which could be evinced by the strengthened glow discharge structure and therefore enhanced space charge effect.