Ultra-short pulsed non-equilibrium atmospheric pressure gas discharges

This thesis presents experimental studies of various non-thermal atmospheric pressure gas discharges generated using short pulsed excitation as an alternative to widely used sinusoidal excitation. Several pulse generators are detailed that provide high voltage pulses ranging from hundreds of microseconds to less than ten nanoseconds in duration. A key enabler to the generation of a stable discharge is a suitably high repetition rate; this prerequisite precludes many conventional pulsed power technologies. Fortunately, recent advances in semiconductor technology have made it possible to construct solid state switches capable of producing high voltage pulses with repetition rates of many kilohertz. Pulsed excitation introduces many opportunities to tailor the applied voltage and consequently enhance the discharge which are not possible with sinusoidal excitation sources. Through detailed electrical and optical analysis it is shown that pulsed excitation is not only more energy efficient than a comparable sinusoidal source but produces a higher flux of excited species that are essential in many applications. When pulse widths are reduced to a sub-microsecond timescale a novel barrier-free mode of operation is observed. It is shown that diffuse large area plasmas are easily produced at kilohertz repetition rates without the usually indispensable dielectric barriers. Experimental results show that a short pulse width prevents the onset of the undesirable glow-to-arc transition thus introducing an added degree of stability. A further benefit of pulsed excitation is the ability to produce gas discharges with a high instantaneous peak power yet low average power consumption, resulting in a high density plasma that exhibits roomtemperature characteristics. Finally, as an acid test to highlight the many benefits of pulsed excitation several real-world applications are considered. It is shown that in all cases pulsed gas discharges provide real benefits compared to their sinusoidal counterparts

White paper on the future of plasma science and technology in plastics and textiles

This is the peer reviewed version of the following article: “Uros, C., Walsh, J., Cernák, M., Labay, C., Canal, J.M., Canal, C. (2019) White paper on the future of plasma science and technology in plastics and textiles. Plasma processes and polymers, 16 1 which has been published in final form at [doi: 10.1002/ppap.201700228]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."This white paper considers the future of plasma science and technology related to the manufacturing and modifications of plastics and textiles, summarizing existing efforts and the current state‐of‐art for major topics related to plasma processing techniques. It draws on the frontier of plasma technologies in order to see beyond and identify the grand challenges which we face in the following 5–10 years. To progress and move the frontier forward, the paper highlights the major enabling technologies and topics related to the design of surfaces, coatings and materials with non‐equilibrium plasmas. The aim is to progress the field of plastics and textile production using advanced plasma processing as the key enabling technology which is environmentally friendly, cost efficient, and offers high‐speed processingPeer ReviewedPostprint (author's final draft

Room-temperature atmospheric argon plasma jet sustained with submicrosecond high-voltage pulses

In this letter, an experimental study is presented to characterize a room-temperature plasma jet in atmospheric argon generated with submicrosecond voltage pulses at 4 kHz. Distinct from sinusoidally produced argon discharges that are prone to thermal runaway instabilities, the pulsed atmospheric argon plasma jet is stable and cold with an electron density 3.9 times greater than that in a comparable sinusoidal jet. Its optical emission is also much stronger. Electrical measurement suggests that the discharge event is preceded with a prebreakdown phase and its plasma stability is facilitated by the short voltage pulses

Sharp bursts of high-flux reactive species in submicrosecond atmospheric pressure glow discharges

In this letter, the authors present an experimental study of the temporal characteristics of submicrosecond pulsed atmospheric glow discharges. Using electrical measurements and nanosecond-resolved optical emission spectroscopy, they show that a long initial period of each voltage pulse is spent building up space charges and is then followed by a large current pulse in the voltage-falling phase. Reactive plasma species such as oxygen atoms and OH radicals are produced in a train of sharp and independent pulses of 50–100 ns wide. Finally, their production is shown to increase significantly as the voltage pulse width reduces or the repetition frequency increases

Contrasting characteristics of linear-field and cross-field atmospheric plasma jets

This letter reports an experimental study of two types of atmospheric pressure plasma jets in terms of their fundamental properties and their efficiency in etching polymeric materials. The first plasma jet has a cross-field configuration with its electric field perpendicular to its gas flow field, whereas the second is a linear-field device having parallel electric and flow fields. The linear-field jet is shown to drive electron transportation to the downstream application region, thus facilitating more active plasma chemistry there. This is responsible for its etching rate of polyamide films being 13-fold that of its cross-field counterpart

10 ns pulsed atmospheric air plasma for uniform treatment of polymeric surfaces

This letter reports an experimental study of a 10 ns pulsed dielectric barrier discharge in atmospheric air, excited with a train of 65 ns voltage pulses at a repetition frequency of 5 kHz. It is shown that these ultrashort pulses produce a homogenous discharge with very high electron density in excess of 1013 cm−3 and low gas temperature, which are particularly desirable for uniform treatment of thermally sensitive polymer films. Their treatment of polypropylene films is found to introduce microscale surface patterns as well as various carbon-oxygen bonds, both useful for improving the hydrophilic properties of polymeric materials

Frequency effects of plasma bullets in atmospheric glow discharges

Pointlike plasma bullets have been reported in atmospheric plasma jets below 50 kHz. This paper presents 10-ns images of both pointlike and striplike plasma bullets generated at frequencies between 80 and 394 kHz. The striplike plasma bullets are always present, whereas the pointlike ones are suppressed at sufficiently high frequencies. Abel-converted images show that the pointlike plasma bullets have a long tail of 4.5 cm extended to the anode region