An atmospheric pressure plasma jet generated in Ar/water vapor mixtures has been investigated and the effect of water content on plasma properties has been studied. Plasma generated in Ar/water ͑0.05%͒ mixture shows higher intensity of OH radicals in emission spectra than pure argon alone. Plasma density has been estimated from current measurement and is in order of 1.5ϫ 10 13 cm −3 . Electron temperature has been estimated as 0.97 eV in pure Ar and it decreases with an increase in water content in plasma. The gas temperature has been determined by fitting of the experimental spectra and using the Boltzmann plot method. The gas temperature increases with the addition of water to feed gas from 620 K in pure Ar up to 1130 K for 0.76% H 2 O.

An atmospheric pressure plasma jet generated in Ar with water vapor is investigated. It is shown that an increase in the water content results in a decrease in the input power and asymmetry of the current waveform on positive and negative half-periods of the applied voltage. Space-resolved spectroscopy with a resolution of 1 mm and an imaging technique are applied for the characterization of the afterglow and investigation of the influence of water content on plasma properties. The rotational temperature of the jet is determined by simulation of the OH radical emission spectrum, transition A 2 + (v = 0) → X 2 (v = 0). It is revealed that the temperature of the discharge increases from 450 K (Ar) up to 850 K with an increase in the water content up to 7600 ppm. Generation of the discharge in mixtures of argon with water vapor at a concentration of 350 ppm results in a maximal yield of OH radicals that can be useful in plasma jet applications. Preliminary tests of polypropylene surface modification are carried out in order to estimate the influence of water content on the results of treatment.

In this work, we have applied optical emission spectroscopy diagnostics to investigate the characteristics of a non-thermal atmospheric pressure helium plasma jet. The discharge characteristics in the active and afterglow region of the plasma jet, that are critical for biomedical applications, have been investigated. The voltage-current characteristics of the plasma discharge were analyzed and the average plasma power was measured to be around 18 W. The effect of addition of small fractions of oxygen at 0.1%-0.5% on the plasma jet characteristics was studied. The addition of oxygen resulted in a decrease in plasma plume length due to the electronegativity property of oxygen. Atomic and molecular lines of selected reactive plasma species that are considered to be useful to induce biochemical reactions such as OH transitions A 2 R þ ð ¼ 0; 1Þ ! X 2 PðD ¼ 0Þ at 308 nm and A 2 R þ ð ¼ 0; 1Þ ! X 2 PðD ¼ 1Þ at 287 nm, O I transitions 3p 5 P!3s 5 S 0 at 777.41 nm, and 3p 3 P!3s 3 S 0 at 844.6 nm, N 2 (C-B) second positive system with electronic transition C 3 P u ! B 3 P g in the range of 300-450 nm and N 2 þ (B-X) first negative system with electronic transition B 2 R þ u ! X 2 R þ g ðD ¼ 0Þ at 391.4 nm have been studied. The atomic emission lines of helium were identified, including the He I transitions 3p 3 P 0 !2s 3 S at 388.8 nm, 3p 1 P 0 ! 2s 1 S at 501.6 nm, 3d 3 D!2p 3 P 0 at 587.6 nm, 3d 1 D!2p 1 P 0 at 667.8 nm, 3s 3 S 1 !2p 3 P 0 at 706.5 nm, 3s 1 S 0 !2p 1 P 0 at 728.1 nm, and H a transition 2p-3d at 656.3 nm. Using a spectral fitting method, the OH radicals at 306-312 nm, the rotational and vibrational temperatures equivalent to gas temperatures of the discharge was measured and the effective non-equilibrium nature of the plasma jet was demonstrated. Our results show that, in the entire active plasma region, the gas temperature remains at 310 6 25 K and 340 6 25 K and it increases to 320 6 25 K and 360 6 25 K in the afterglow region of the plasma jet for pure helium and helium/oxygen (0.1%) mixture, respectively. Additionally, the vibrational temperatures range from 2200 6 100 K and 2500 6 100 K for pure helium and helium/oxygen (0.1%) mixture, respectively. The plasma jet was tested on heat sensitive polymer films used in biomedical applications such as polyethylene terephthalate and poly-L-lactide samples continuously for several minutes without causing any physical or thermal damage to the films. The plasma jet produces significant reactive species of interest while the gas temperatures remain very low demonstrating its potential for a range of biomedical applications. V C 2013 AIP Publishing LLC. [http://dx.

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A streamer-to-spark transition in a self-pulsing transient spark (TS) discharge of positive polarity in air was investigated using cross-correlation spectroscopy. The entire temporal evolution of the TS was recorded for several spectral bands and lines: the second positive system of N 2 (337.1 nm), the first negative system of N 2 + (391.4 nm), and atomic oxygen (777.1 nm). The results enable the visualization of the different phases of discharge development including the primary streamer, the secondary streamer, and the transition to the spark. The spatio-temporal distribution of the reduced electric field strength during the primary streamer phase of the TS was determined and discussed. The transition from the streamer to the spark proceeds very fast within about 10 ns for the TS with a current pulse repetition rate in the range 8-10 kHz. This is attributed to memory effects, leading to a low net electron attachment rate and faster propagation of the secondary streamer. Gas heating, accumulation of species such as oxygen atoms from the previous TS pulses, as well as generation of charged particles by stepwise ionization seem to play important roles contributing to this fast streamer-to-spark transition.

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