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A laser initiation and radio frequency (rf) sustainment technique has been developed and improved from our previous work to create and sustain large-volume, high-pressure air and nitrogen plasmas. This technique utilizes a laser-initiated, 15 mTorr partial pressure tetrakis (dimethylamino) ethylene seed plasma with a 75 Torr background gas pressure...
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Context 1
... rf circuit diagram is shown in Fig. 2. A 25 kW maximum power 13.56 MHz rf generator CXH25K, Com- del, Inc. is used to deliver power to the antenna using an efficient capacitive impedance matching network. The short 20 ns laser pulse is triggered late during the initial rise of the rf power at the point when the forward rf power is 90% of the power setting, in order to ...
Context 2
... order to match the varying plasma load impedance, the four capacitors in Fig. 2 are preset following the work of Kelly et al., 35 ...
Context 3
... 0 =50 rf network by C 1 and C 2 , and the plasma impedance at a later time can be matched by C 1 + C a and C 2 −1 + C b −1 −1 . A control circuit is required so that these two sets of matching networks can be switched when the plasma is formed. To this end, we have designed and utilized a dy- namic rf measurement and matching system. This system Fig. 2 has three major parts. The first is a rf detector circuit that is composed of a dual directional coupler, a pair of rf detectors, an operational amplifier circuit, and a metal oxide semiconductor field effect transistor MOSFET amplifier. This circuit detects the incident and reflected rf power levels and compares them at the ...
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Citations
... We used Specair software to fit the OES of N2 + (B-X) to derive the gas temperature under experimental conditions. Electrons gain energy from the electric field and transfer it to other particles through collisions; the vibrational excitation of N2 helps to lower the dissociation potential barriers to produce more intermediate species [49]. Figure 8 shows the effect of noble gas addition on gas temperature. ...
... We used Specair software to fit the OES of N 2 + (B-X) to derive the gas temperature under experimental conditions. Electrons gain energy from the electric field and transfer it to other particles through collisions; the vibrational excitation of N 2 helps to lower the dissociation potential barriers to produce more intermediate species [49]. Figure 8 shows the effect of noble gas addition on gas temperature. ...
Non-thermal plasma driven ammonia synthesis has great potential for future industrial applications due to its low theoretical energy requirements. To achieve technological advancement and environmental sustainability, it is crucial to boost the energy yield in plasma-assisted ammonia synthesis. Therefore, optimizing energy transfer and utilization are key strategies for enhancing energy efficiency. In this study, dielectric barrier discharge driven by a nanosecond pulsed power supply is used to enhance plasma-assisted ammonia synthesis by controlling the energy transfer through the addition of noble gases. It was found that the addition of noble gases changed the plasma characteristics, significantly improved the uniformity of the discharge, and achieved a high energy yield for ammonia synthesis. The effects of additive amounts of argon (Ar) and helium (He), as well as the pulse parameters including the pulse voltage, pulse repetition frequency, pulse width, and pulse rise time on the energy yield of ammonia synthesis are discussed. The inclusion of noble gases expanded the pathway for gas-phase reactions, with the active components of critical reactions examined through optical emission spectra. This analysis revealed an increased presence of both N2+ and N2* particles in the reaction’s rate-limiting step, attributed to the addition of noble gases. Finally, a zero-dimensional (0D) plasma chemical kinetic model was established to investigate the influence of Ar addition on the reaction mechanism of ammonia synthesis.
... As a quantitative indicator, the gas temperature of FEGLD is acquired and discussed. Since the small energy gap between the rotational levels of the molecules, the translational-rotational equilibrium is readily achieved by frequent collisions between the heavy particles at AP [40]. The gas temperature can be considered approximately equal to the rotational temperature, and it can be acquired by analyzing the rotational spectra of excited molecular species [41,42]. ...
... As a quantitative indicator, the gas temperature of FEGLD is acquired and discussed. Since the small energy gap between the rotational levels of the molecules, the translationalrotational equilibrium is readily achieved by frequent collisions between the heavy particles at AP [40]. The gas temperature can be considered approximately equal to the rotational temperature, and it can be acquired by analyzing the rotational spectra of excited molecular species [41,42]. ...
In this paper, a high-density gas–liquid discharge plasma is obtained combined with nanosecond pulse voltage and a floating electrode. The discharge images, the waveforms of pulse voltage and discharge current, and the optical emission spectra are recorded. Gas temperature and electron density are calculated by the optical emission spectra of N2 (C3Πu → B3Πg) and the Stark broadening of Hα, respectively. The emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), He (3d3D → 3p3P20), gas temperature, and electron density are acquired by optical emission spectra to discuss plasma characteristics varying with spatial distribution, discharge gap, and gas flow rate. The spatial distributions of discharge characteristics, including gas temperature, electron density, and emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), and He (3d3D → 3p3P20), are presented. It is found that a high-density discharge plasma with the electron density of 2.2 × 1015 cm−3 and low gas temperature close to room temperature is generated. While setting the discharge gap distance at 10 mm, the discharge area over liquid surface has the largest diameter of 20 mm; under the same conditions, electron density is in the order of 1015 cm−3, and gas temperature is approximately 330 K. In addition, the discharge plasma characteristics are not kept consistent in the axial direction, in which the emission intensities of N2+ (B2Σ → X2Π), N2 (C3Πu → B3Πg), OH (A2Σ → X2Π), and gas temperature increased near the liquid surface. As the discharge gap is enlarged, the gas temperature increases, whereas the electron density remains almost constant. Moreover, as the gas flow rate was turned up, the electron density increased and the gas temperature was kept constant at 320 K.
... The vibrational temperature T vib and rotational temperature T rot of plasma can be obtained according to the temperature set in the software. The rotational energy and translational energy of molecules are generally considered to be able to reach equilibrium due to the frequent collisions in atmospheric air, which means that the gas temperature of the plasma and rotational temperature of the molecules are equal [64,65]. Therefore, the gas temperature under different conditions can be obtained by OES. ...
The time evolution of dielectric barrier discharge driven by nanosecond pulse high-voltage power is investigated by high-speed video analysis, electrical measurements and spectral diagnostics. It is found that the discharge mode generally goes through the evolution process of filamentary discharge → diffuse discharge → filamentary discharge with the increase in discharge cycle. The time-dependent changes in the standard deviation of image gray levels indicate that the discharge uniformity first improves and then deteriorates in this evolution process. The different pre-ionization density and modulated distribution of space charges and surface charges are considered to be the main reasons for the time evolution of discharge uniformity. In addition, the experiments under different frequencies and voltages show that the transition of the discharge mode is more likely to occur at higher frequency and higher voltage. Further measurement and calculation reveal that the discharge at high frequency and high voltage has the same characteristics, that is, high pre-ionization degree, thick filament diameter and short time lag. These characteristics usually lead to higher seed electron density, larger critical avalanche size and weaker lateral inhibition effect, which make the discharge mode transition more likely to occur.
... It is reported that the gas temperature of plasma used to be considered as the temperature of heavy particles, which is also close to the molecular rotational temperature Trot. 33 Therefore, the impacts of gas humidity on the rotational temperature Trot of plasmas at the nozzle under various input powers are investigated in this section. In this paper, Trot is diagnosed by the OH(A 2 Σ + − X 2 ∏) radical and fitted by the LIFBASE software. ...
This paper investigated the influence of gas humidity (1%, 3%, 8%, 10%, and 12%) on the characteristics of a microwave-induced atmospheric plasma jet. The plasma discharge was generated by a microwave solid-state source with a H2O–Ar mixture gas flow of 8.1 L/min. The variation in energy efficiency, O and OH concentrations, rotational temperature of heavy species, shapes of plasma plumes with different humidities, and microwave input powers were recorded and analyzed. The results showed that the concentrations of O and OH increase monotonously with gas humidity at higher input powers while they fluctuate with gas humidity at lower input powers. With an increase in the H2O/Ar ratio from 1% to 12%, the energy efficiency of the plasma generator decreases, and the plasma plumes become shorter and thinner. The rotational temperature of plasma at the nozzle also showed positive correlation with increasing humidity. Adding more input power would make all the values of these parameters increase. This paper is supposed to be helpful for the research of the interaction mechanism of mix gas plasma and microwave power and for improving the effect of plasma treating biomedical materials.
... A recent study [5] has investigated a quantitative correlation between the initiation carrier density and the breakdown voltage where a threshold carrier density of 3 × 10 11 cm −3 was found for a significant reduction in the breakdown voltage across a gap of 300 µm. As a means of injecting initiation carriers, thermal [3] or UV [6] methods have been investigated, but they may not be suitable for microscale integration due to either its poor injection efficiency or its process incompatibility. For its implementation in practical use, the integration of an initiation carrier injector on the same substrate along the primary discharge electrodes is highly desirable. ...
A dielectric barrier discharge (DBD)-integrated plasma device for low-voltage atmospheric plasma generation is presented. By utilizing DBD afterglows as initiation carriers, a significant reduction in the breakdown voltage across a gap of 1 mm was achieved. The use of integrated DBD offers a precise control of initiation carrier injection and suppresses sputtering-induced electrode wear. The proposed integration scheme enables a highly reliable atmospheric plasma generation on a substrate at a very low voltage. This study also reveals that the injection location and the amount of initiation carriers play a key role in triggering avalanche breakdown process in the discharge. An optimized device structure has demonstrated atmospheric plasma across a gap of 1 mm at 700 V, which is only one-third of the breakdown voltage using a conventional two-electrode structure.
... is regarded as a reliable method for calculating the gas temperature of NPD plasma. The equilibrium between translational and rotational motion is easily achieved by the frequent collisions of heavy particles, so that the gas temperature of the plasma is approximately equal to the rotational temperature of N 2 [36][37][38]. The rotational temperature of N 2 + (B 2 ∑ u + →X 2 ∑ g + ) can be acquired by the Specair code [38]. ...
In this study, nanosecond pulsed discharge plasma is employed to treat the XAD-2 resins in the purpose of improving its adsorption capacity of polycyclic aromatic hydrocarbons. The discharge images, waveforms of pulse voltage and discharge current, and optical emission spectra are measured to investigate the plasma characteristics. The scanning electron microscopy, N 2 adsorption-desorption analysis, Fourier transform infrared spectrum, and x-ray photoelectron spectroscopy are employed to characterize the physical and chemical properties of raw and modified XAD-2 resins. It is found that the adsorption capacity of modified XAD-2 resins for polycyclic aromatic hydrocarbons is obviously improved. The adsorption capacity of XAD-2 resins modified by plasma increased by 70% in 10 min adsorption time under the optimal conditions of 20 min treatment time and artificial air. The reason for the improved adsorption capacity is attributed to the increase of specific surface area, the number of 28–33 nm micro-mesopores, and relative intensity of oxygen-containing functional groups (C=O, C–O, and COOH). The possible mechanism of plasma modification of XAD-2 resin is also proposed.
... In atmospheric pressure plasma, the rotational temperature (T rot ) can be considered equal to the T g , because the little space of rotational energy levels can make rotational energy and translational energy into balance easily. 30 Generally, T g is determined by the T rot of N 2 (C-B), 31 but there is almost no N 2 (C-B) spectral for GLDOP due to its ambient gas of pure oxygen. The T rot of OH (A-X) is another credible approach to estimate T g , 32,33 and the intense OH (A-X) emission band can be obtained in GLDOP, as shown in Fig. 6. ...
In this paper, a capacitor assisted AC high-voltage was employed to generate a gas–liquid discharge in pure oxygen at atmospheric pressure. The discharge images, waveforms of voltage and discharge current, and optical emission spectra of plasma were diagnosed for the purpose of investigating the discharge modes. The gas temperature (Tg), excitation temperature of hydrogen (Texc), and electron density (ne) were calculated by the spectra of OH (A²Σ–X²Π), the intensity ratio of Hα and Hβ, and the Stark broadening of Hβ, respectively. The effects of applied voltage and capacitance value on the mode transition of discharge were also discussed. It is found that due to the presence of capacitor, not only is the unlimited growth of discharge current restrained, but the transition of discharge mode is also controllable. There are three discharge modes of gas–liquid discharge oxygen plasma (GLDOP), and with the increase of applied voltage or capacitance value, discharge modes are transited from the streamer mode, to the glow-like mode, and to the abnormal glow/arc mode. With the mode transition, the Tg and Texc of GLDOP increase and the ne decreases. In contrast, the change of Tg and ne is negligible when GLDOP maintains one kind of discharge mode.
... Due to a small energy gap between the rotational levels, the equilibrium between the translational motion and the rotational motion is easily achieved by frequent collisions between the heavy particles at atmospheric pressure [39]. The plasma gas temperature is approximately equal to the rotational temperature of N 2 . ...
... In the discharge at atmospheric pressure, the gas temperature also equals the gas temperature in the atmospheric pressure discharge. [34,35] The software ...
Transitions between the streamer and spark modes affect the stability of gas–liquid discharges, limiting their practical applications, while the nature of such transitions is poorly understood. Here we clarify the often neglected effect of a dielectric on the gas–liquid discharge stability, using direct and indirect grounding configurations. Discharge modes and plasma characteristics in these two configurations are investigated. The discharge appears in a transient spark mode in the direct grounding while in a streamer mode in the indirect case. It is shown that the dielectric significantly improves the discharge stability. The gas temperature and electron density in the transient spark are 380 K and 1017/cm3 with a 30 kV pulse voltage, respectively, which are higher than those in the streamer mode. Gas–liquid discharge is one of the hottest research topics in the area of nonequilibrium plasmas, in which stability is a key factor. This paper aims to present the effect of a dielectric on the stability of gas–liquid discharge, by comparing the discharge modes and plasma characteristics of nanosecond pulse gas–liquid discharge in atmospheric nitrogen with two different grounding configurations.
... In discharge at atmospheric pressure, the gas temperature of the plasma is approximately equal to the rotational temperature [40]. In this paper, the emission spectrum of the OH(A 2 → X 2 , 0-0) band in the range 306-312 nm at the quartz nozzle is used to estimate the rotational temperature using the LIFBASE software [41]. ...
The pulse-modulated radio frequency (RF) and kHz sinusoidal voltages are used for the excitation of two plasma jets, for which the reactive species in the plasma plumes and in the treated water are comparatively studied. With the same discharge power, it is found that concentrations of aqueous reactive species generated by the kHz sinusoidal plasma jet are higher than that of the pulse-modulated RF plasma jet, especially for the short-lived species OH. In addition, the comparison between the bacterial inactivation results is in accordance with that for the concentrations of aqueous reactive species for the two types of plasma jets. On the contrary, the emission spectra indicate that the gaseous reactive species such as OH(A) and O(3p5P) have much higher densities for the pulse-modulated RF plasma jet, which should ascribe to its higher electron density and electron temperature. Moreover, the concentrations of the aqueous reactive species and the emission intensities of the gaseous reactive species have similar variation trends for each of the plasma jets, as a function of the discharge power and the gap width. These results imply that the emission intensity could not reflect the relative concentration of an aqueous reactive species between these two plasma jets, but it could be used as an indicator of the concentration variation of an aqueous reactive species for each of the plasma jets. In addition, the phenomenon of electron trapping effect also indicates that the aqueous reactive species can be effectively generated only when more electrons act on the water sample.
