# Influence of Nitrogen Admixture on Plasma Characteristics in a dc Argon Glow Discharge and in Afterglow

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}admixture on the current–voltage characteristic of a diffuse glow discharge; influence of N

_{2}admixture on the rate of plasma decay in the afterglow; influence of N

_{2}admixture on discharge constriction conditions and on the characteristics of constriction process; formation of partially constricted discharge in Ar:N

_{2}mixtures at intermediate gas pressures.

## 2. Influence of N_{2} Admixture on the Current–Voltage Characteristic of a Diffuse Glow Discharge in Ar

_{2}molecules by electron impact are rather high in the energy range 2–3.5 eV (i.e., at energies below the energy of the lower argon metastable state), so in Ar:N

_{2}discharge plasma the electron energy losses due to excitation of vibrational levels can be significant. Moreover, in Ar:N

_{2}plasma metastable states of Ar atoms are effectively quenched in collisions with N

_{2}molecules [31]

_{2}→ Ar + N

_{2}(C

^{3}П

_{u}), rate constant = 2.9 × 10

^{−11}cm

^{3}s

^{−1},

_{2}→ Ar + N

_{2}(B

^{3}П

_{g}), rate constant = 6.0 × 10

^{−12}cm

^{3}s

^{−1}.

_{2}and Ar + 1%N

_{2}gas mixtures at gas pressure P = 2 Torr (R = 1.4 cm, interelectrode distance ≈ 75 cm). One can see that the discharge voltage increases with a factor 2 when 1% of nitrogen is added to argon.

_{2}mixtures [15,16,34]. Figure 2 shows current–voltage characteristics measured in pure argon and in Ar + 0.75%N

_{2}and Ar + 1%N

_{2}gas mixtures at gas pressure P = 40 Torr (R = 1.4 cm, interelectrode distance ≈ 75 cm). As can be seen from Figure 2, the discharge voltage of a diffuse discharge decreases by 2–1.5 times (depending on discharge current value) when 0.75% of nitrogen is added to argon. In the case of 1% of nitrogen the effect is slightly less pronounced.

_{2}mixture were studied both experimentally and theoretically (R = 1.4 cm, interelectrode distance ≈ 75 cm). To reproduce in the calculations the current–voltage characteristics measured at various pressures (2 Torr, 40 Torr and 80 Torr, see Figure 3), a rather complex (complete) zero-dimensional kinetic model was elaborated [17]. The model included kinetics of excited states of Ar atoms (four lower levels and the higher states combined into three lumped levels), the kinetics of electronic levels of N

_{2}(N

_{2}(A${}^{3}{\Sigma}_{\mathrm{u}}^{+}$), N

_{2}(B

^{3}Π

_{g}), N

_{2}(B’${}^{3}{\Sigma}_{\mathrm{u}}^{-}$), N

_{2}(a’${}^{1}{\Sigma}_{\mathrm{u}}^{-}$), N

_{2}(a

^{1}Π

_{g}), N

_{2}(w

^{1}Δ

_{u}), and N

_{2}(C

^{3}Π

_{u})), the vibrational kinetics of nitrogen molecules in the ground state N

_{2}(X${}^{1}{\Sigma}_{\mathrm{g}}^{+}$, v) (45 vibrational levels), the kinetics of electronic states of N atoms (N(

^{4}S), N(

^{2}D), and N(

^{2}P)), and the kinetics of electrons and Ar

^{+}, ${\mathrm{Ar}}_{2}^{+}$, N

^{+}, ${\mathrm{N}}_{2}^{+}$, ${\mathrm{N}}_{3}^{+}$, and ${\mathrm{N}}_{4}^{+}$ ions. Electron transport coefficients and rate constants for electron induced processes were calculated by solving the electron Boltzmann equation in parallel with the system of kinetic equations. Besides, the model included the equation for the electric circuit.

_{2}, pressure of 50 Torr, tube diameter of 3.8 cm, and currents of 5–50 mA). In that paper, the gas temperature was also estimated using the procedure described above. It was shown that for the case of gas mixture the calculated values of the gas temperature agreed quite well with the measured ones. For pure Ar discharge the estimated gas temperatures were lower than measured. This was explained by the fact that, under considered conditions, the discharge in argon contracted at approximately 35 mA whereas the discharge in mixture remained diffuse even at 200 mA. In pure Ar, at discharge currents relatively close to 35 mA the radial profile of the deposited energy is noticeably narrower than the Besselian profile and, as a result, the measured temperature profile is narrower than the calculated one (for example, at I = 20 mA, see comments in [35]). Naturally, with decreasing current, the radial profile of the discharge current density becomes wider, and the theoretical estimate of the gas temperature becomes more reliable. In [17], the relatively low discharge currents were considered (≤20 mA), so it can be expected that the performed estimation of the gas temperature was rather correct.

_{2}mixture for P = 2 Torr and 40 Torr are shown in Figure 4. According to calculations, at P = 40 Torr, the gas temperature in pure Ar discharge is higher than in Ar + 1%N

_{2}mixture discharge, which is consistent with experimental data [35].

_{2}mixture) with discharge current increase from 2 mA to 20 mA. That is, in argon, the reduced electric field is two times higher than in the mixture. At low pressure (2 Torr) the E/N value varies from 7.59 Td to 6.6 Td (in pure Ar) and from 22.5 Td to 10.9 Td (in Ar + 1%N

_{2}mixture) with discharge current increase from 2 mA to 20 mA.

_{2}

^{+}. Losses of electrons were mainly provided by recombination with Ar

_{2}

^{+}ions and, partially, by ambipolar diffusion.

_{2}mixture at intermediate pressures, a very effective ionization mechanism was realized. The ionization was mainly provided by processes of associative ionization of excited nitrogen atoms

^{2}P) + N(

^{2}D) →N

_{2}

^{+}+ e,

^{2}P) + N(

^{2}P) →N

_{2}

^{+}+ e,

_{2}(a’

^{1}Σ

_{u}

^{−}) + N

_{2}(A

^{3}Σ

_{u}

^{+}) → N

_{4}

^{+}+ e.

_{2}(a’

^{1}Σ

_{u}

^{−}) + N

_{2}(a’

^{1}Σ

_{u}

^{−}) → N

_{4}

^{+}+ e.

_{2}(A

^{3}Σ

_{u}) + N

_{2}(X, 14 ≤ v ≤ 19) → N

_{2}(B

^{3}Π

_{g}, v ≥ 13) + N

_{2}(X) → N + N + N

_{2}(X),

_{2}(a’) molecules

_{2}(X, v ≥ 16) + N

_{2}(X, v ≥ 16) → N

_{2}(a’) + N

_{2}(X, v = 0)

_{2}

^{+}+ Ar ↔ N

_{2}+ Ar

^{+},

^{+}+ 2Ar ↔ Ar

_{2}

^{+}+ Ar,

_{2}

^{+}, i.e., the same as in pure Ar discharge.

^{2}D) and N(

^{2}P) states are 2.38 eV and 3.57 eV, respectively. Nitrogen atoms are produced in processes (5) with the participation of vibrationally excited molecules N

_{2}(X, 14 ≤ v ≤ 19) and electronically excited N

_{2}(A) molecules. Lower vibrational levels of N

_{2}molecules (v ≤ 8) are excited by electron impact, the threshold for the excitation of the first vibrational level is about 0.29 eV. The upper vibrational levels are populated due to V–V exchange processes. The lower metastable state N

_{2}(A

^{3}Σ

_{u}) is excited by electron impact from the ground electronic state N

_{2}(X, v), the energy of the N

_{2}(A

^{3}Σ

_{u}) state is about 6.17 eV. One can see that the energies of key species, which provide ionization in Ar + 1%N

_{2}mixture at intermediate pressures, are essentially lower than 11.6 eV. For this reason, the ionization mechanism in Ar + 1%N

_{2}mixture is realized at E/N values noticeably lower than those in pure Ar.

_{2}to Ar leads to more effective ionization processes, while the major ion in plasma and, thus, the mechanisms of electron losses remain the same. As a result, the electric field in Ar + 1%N

_{2}discharge (and the reduced electric field) is lower than that in the pure argon discharge.

_{2}mixture are due to ambipolar diffusion, the rate of losses is noticeably higher than that at intermediate pressures (e.g., 40 Torr). For this reason, the reduced electric field E/N in the plasma increases [17], because, in order to preserve ionization balance in the discharge plasma, it is necessary that the ionization rate be sufficiently high. In pure argon discharge, the required rate of ionization is provided, as before, mainly by stepwise ionization processes. In Ar + 1%N

_{2}discharge at low pressures the Processes (3) and (4) cannot provide the required rate of ionization and the ionization processes involving argon atoms (ionization by electron impact from the ground state, stepwise ionization and chemoionization) contribute substantially to electron production [17]. At that, the value of E/N (and, accordingly, the value of E) in Ar + 1%N

_{2}mixture is appreciably higher than that in pure argon. This is related, in particular, to the fact that, in the mixture, excited argon atoms are efficiently quenched by nitrogen molecules (Processes (1) and (2)).

^{−12}cm

^{3}s

^{−1}, which is lower by one order of magnitude than the estimate given in [37]. The rate constant used in the model [17] was taken from [36]. As for the Process (3b), it was shown in [38] that the use of this process in the model of the afterglow nitrogen plasma allows one to adequately describe specific features of the experimentally observed plasma decay dynamics. According to estimates [38], the rate constant of this process is 2 × 10

^{−11}cm

^{3}s

^{−1}, it is this value that was used in the model [17]. The rate constants of Reactions (4a) and (4b) used in different studies differ by one to two orders of magnitude. In the model [17] rate constants of these processes were chosen in accordance with recommendations made in [39]: 10

^{−11}cm

^{3}s

^{−1}and 5 × 10

^{−11}cm

^{3}s

^{−1}, respectively.

_{2}to Ne also leads to changing the ionization mechanism in dc discharge plasma, ionization processes in Ne + 1%N

_{2}discharge are similar to that in Ar + 1%N

_{2}discharge. On the other hand, in contrast to argon atoms, the ionization energy of Ne atoms is essentially higher than that of N

_{2}molecules, therefore the charge transfer process from N

_{2}

^{+}ion to Ne atom is absent Ne + 1%N

_{2}plasma. For this reason, the addition of N

_{2}to Ne leads to the replacement of Ne

_{2}

^{+}(major ion in plasma in pure Ne) with N

_{4}

^{+}in Ne + 1%N

_{2}mixture. The rate constant for the process of electron recombination with N

_{4}

^{+}ion is one order of magnitude higher than that with Ne

_{2}

^{+}ion. The increase in the rate of electron losses due to recombination with N

_{4}

^{+}ions appears to be more significant factor than the new ionization mechanism, so the electric field needed for the glow discharge maintenance increases with the addition of N

_{2}to Ne. In the case of He, the situation is similar to that in Ne.

## 3. Effect of Nitrogen Addition to Argon on the Rate of Plasma Decay in the Afterglow

_{2}mixture, a very high degree of vibrational excitation of nitrogen molecules is achieved. In the afterglow of such a discharge, the electrons gain energy in superelastic (second kind) collisions with vibrationally excited molecules, so the effective electron temperature (T

_{e}= 2/3u

_{m}, where u

_{m}is the mean electron energy) in the afterglow plasma can be quite high for some time (about the relaxation time of the vibrational distribution function). In turn, the high electron temperature provides the high rate of plasma decay due to ambipolar diffusion process.

_{2}mixture. The vibrational temperature, T

_{v}, of N

_{2}molecules was also experimentally estimated. The discharge was maintained in a cylindrical glass tube of 3 cm internal diameter at gas pressures of 0.5 Torr and 1 Torr. The pulse duration was 40 µs and the pulse repetition frequency was 1 kHz. The estimated vibrational temperature was about 4000–5000 K, and the electron temperature, calculated by the measured EEDFs, was varied in the range 4000–6000 K (depending on the gas pressure and the discharge current). In [3], the electron temperature in the afterglow of Ar:N

_{2}power-pulsed microwave plasma was measured. Measurements were performed in a quartz tube with an inner radius of 0.3 cm in mixtures with N

_{2}percentage of 1–20% at a total gas pressure of 8–30 Torr. It was shown that in mixtures with a relatively low N

_{2}percentage (for example, 1%) the electron temperature in the afterglow plasma can be as high as 0.8 eV, which indicates that the degree of vibrational excitation of nitrogen is high.

_{v}. Calculations of the vibrational distribution function and the EEDF in the afterglow of a dc glow discharge in Ar + 1%N

_{2}were presented in conference paper [44]. In calculations the kinetic model [17] was used, and the procedure of simulation was as follows. Firstly, time–evolution of plasma parameters was calculated up to approaching steady-state discharge conditions which were characterized by the discharge current value. Then, the applied voltage (the electric field in plasma) was switched off, and the time-variation of plasma parameters in the post-discharge was calculated. The following conditions were considered: discharge tube radius R = 1.5 cm, gas pressure P = 5 Torr, gas temperature T

_{gas}= 350 K, discharge current I = 20 mA.

_{e}= 2.0 × 10

^{10}cm

^{–3}. Vibrational distribution functions in discharge and afterglow plasma are shown in Figure 5. The shape of the distribution function (and the degree of the vibrational excitation) can be characterized by ‘local’ vibrational temperatures, T

_{v}

^{i,i+1}, calculated using the populations of two successive vibrational levels, i and i + 1. In the discharge plasma the vibrational temperature T

_{v}

^{0,1}is as high as 10,580 K and in the afterglow, it decreases down to 3300 K during 50 ms (see Table 1). Note also that T

_{v}

^{i,i+1}values (i = 1, 2, 3, 4, see Table 1) are noticeably higher than T

_{v}

^{0,1}values.

_{e}≈ 8520 K, and the further decrease in T

_{e}value is explained by the decrease in the degree of vibrational excitation of nitrogen molecules, which is illustrated in Figure 5 by growth of N

_{2}(X, v = 0) population. At that, even at t = 30 ms the electron temperature is rather high T

_{e}≈ 6590 eV. It is worth noting that the calculated T

_{e}values agree with those measured in the afterglow of a pulsed microwave discharge in the Ar + 1%N

_{2}mixture [3].

_{2}mixture was numerically studied. As in work [44], the kinetic model [17] was used in simulations. The following conditions were considered: discharge tube radius R = 1.4 cm, gas pressures P = 1, 2, and 5 Torr, discharge currents I = 20 mA and 56 mA. Time variation of the effective electron temperature in Ar + 1%N

_{2}afterglow calculated at fixed discharge current I = 20 mA and various gas pressures is shown in Figure 6. As follows from the calculations, the lower the gas pressure, the faster the electron temperature decreases in the discharge afterglow. In the afterglow of a discharge in pure argon, electrons are heated in superelastic collisions with electronically excited atoms. In addition, fast electrons appear in chemoionization processes Ar* + Ar* = Ar + Ar

^{+}+ e (≈7.6 eV). In [26], the electron temperature in the pure argon afterglow was not calculated because of the problem of accounting for the letter process in the Boltzmann equation. On the other hand, it was observed in [3,45] that the electron temperature in the argon afterglow plasma dropped rapidly (during ~100 μs at pressures of 6–30 Torr) to T

_{e}~1200 K. Therefore, in calculations [26], the electron energy distribution function in pure argon afterglow was assumed to be Maxwellian with the temperature T

_{e}= 1000 K or T

_{e}= T

_{gas}(for comparison).

_{2}mixture at a discharge current of I = 20 mA are shown in Figure 7a–c. From Figure 7 it follows that in some cases an increase in the electron concentration is observed at the very beginning of the afterglow. According to calculations, in steady state Ar + 1%N

_{2}discharge plasma under considered conditions, production of electrons is mainly due to associative ionization (3) and (4) and chemoionization (Ar* + Ar* → Ar

^{+}+ Ar + e) processes and losses of electrons are due to ambipolar diffusion process. After turning off the electric field, the mean electron energy instantaneously (within the model used) decreases. The decrease in the mean electron energy leads to the decrease in the rate of electron losses due to ambipolar diffusion process while the rate of electron production remains near the same, since the rates of the ionization processes mentioned above do not depend on the electron temperature. As a result, this leads to an increase in the electron concentration at the very beginning of the afterglow.

_{2}mixture decays noticeably faster than that of a discharge in pure Ar. In this case, the decay of plasma (both in pure argon and in a gas mixture) is governed by the ambipolar diffusion process, the rate of which in Ar + 1%N

_{2}afterglow plasma is high due to the high electron temperature (see Figure 6).

_{2}mixture decreases much slower than in pure argon, although the rate of ambipolar diffusion in argon is significantly lower. As a result, even at t = 13 ms after the end of the discharge, the electron density in Ar + 1%N

_{2}mixture remains slightly higher than that in pure Ar. In contrast, at t > 15 ms, the electron density in pure argon is significantly higher with respect to that in Ar + 1%N

_{2}mixture. This result is explained by two main effects [26]. The first effect consists in the following: at the beginning of the afterglow in pure argon, the Ar

^{+}ions (dominant ions in the discharge plasma) are quickly (~0.3 ms) converted in molecular ions Ar

_{2}

^{+}(see comments in [26]). At the beginning of the afterglow, the rate of plasma decay due to recombination of electrons with molecular ions is higher than that due to the ambipolar diffusion process. The rate of the recombination process decreases with the electron (and ion) concentration decrease, so that, at t > 15 ms, the plasma decay is governed by the ambipolar diffusion only.

_{2}afterglow the high rate of plasma decay due to ambipolar diffusion process is balanced (to a large extent) by the high rate of electron production via associative ionization of excited nitrogen atoms and molecules (3) and (4). As a result, the plasma decay rate during 1 ms after the end of the discharge is appreciably lower than in the Ar afterglow plasma.

## 4. Effect of Nitrogen Addition to Argon on Discharge Constriction Conditions

_{C}, the discharge positive column sharply constricts to a narrow cord. Simultaneously the sharp bend of the discharge volt-amp characteristic (VAC) occurs (Figure 8). Current values for the transition from the diffuse form to the constricted one and, vice versa, from the constricted form to the diffuse differ, so that hysteresis occurs.

_{C}value depends strongly on the gas pressure and discharge tube diameter. In the context of this paper, it is important that even a small nitrogen admixture to argon also affects essentially the I

_{C}and the whole VAC. This effect is illustrated by Figure 9, where the set of data for pure argon and argon with various nitrogen admixtures is depicted. The discharge tube inner diameter is 2.8 cm, the distance between electrodes is 75 cm. One can see that as low as 0.02 and 0.075 percentage of nitrogen admixtures shifts the critical current from 17 mA to 45 mA and to even 100 mA, respectively. Increasing N

_{2}concentration up to 1 percent makes it impossible to reach constricting for the given electrical scheme. The qualitative explanation of this effect is as follows. As it was mentioned above, it is e–e collisions that provide the conditions necessary for the stepwise discharge constriction. The degree of the influence of e–e collisions on electron energy spectrum depends, in particular, on the ratio of the e–e collision frequency and the frequency of electron energy losses in elastic and inelastic collisions with atoms and molecules. The higher the percentage of nitrogen admixture, the higher the rate (frequency) of electron energy losses due to excitation of vibrational and electronic levels of nitrogen molecules and, consequently, the higher electron concentration (discharge current) is needed to provide the conditions for the discharge constriction.

_{2}addition also diminishes drastically the discharge voltage in the diffuse region. This issue was discussed in Section 2. At the same time, VACs in the constricted region go approximately along the same curve. As is shown in [16], it can be explained by the fact that, due to a very high electron density in a constricted discharge, N

_{2}addition has very little influence on ionization mechanism which in Ar and Ar-N

_{2}cases is mainly stepwise ionization of Ar metastables.

## 5. Effect of Nitrogen Addition to Argon on the Characteristics of Constriction Process

_{C}value only slightly, then the constriction begins near one of the electrodes and then its front propagates toward the other electrode with a finite speed. It seems that this speed can correlate with a group velocity of moving strata whose appearance accompanies the discharge constriction [46]. Experiments with Ar-N

_{2}mixtures showed that a small nitrogen addition affected the constriction front speed.

## 6. Formation of Partially Constricted Discharge in Ar:N_{2} Mixtures at Intermediate Gas Pressures

## 7. Conclusions

_{2}discharge, which provides a high electron temperature in the afterglow due to superelastic collisions of electrons with vibrationally excited molecules. This, in turn, leads to an increase in the rate of plasma decay due to ambipolar diffusion process.

_{2}mixture, the transition time is considerably longer than in pure argon. By proper variation of power supply voltage during the transition, in the case of the Ar:N

_{2}mixture, there can be formed a steady-state partially constricted discharge in which the constricted and diffuse forms of the positive column simultaneously exist in the discharge tube.

## Author Contributions

## Funding

## Conflicts of Interest

## References

- Sá, P.A.; Loureiro, J. A time-dependent analysis of the nitrogen afterglow in N
_{2}and N_{2}–Ar microwave discharges. J. Phys. D Appl. Phys.**1997**, 30, 2320–2330. [Google Scholar] [CrossRef] - Henriques, J.; Tatarova, E.; Dias, F.M.; Ferreira, C.M. Spatial structure of a slot-antenna excited microwave N
_{2}–Ar plasma source. J. Phys. D Appl. Phys.**2008**, 103, 103304. [Google Scholar] [CrossRef] - Hübner, S.; Carbone, E.; Palomares, J.M.; van der Mullen, J. Afterglow of argon plasmas with H
_{2}, O_{2}, N_{2}, and CO_{2}admixtures observed by Thomson scattering. Plasma Process. Polym.**2014**, 11, 482–488. [Google Scholar] [CrossRef] - Tochikubo, F.; Petrović, Z.L.; Nakano, N.; Makabe, T. Influence of Ar Metastable on the Discharge Structure in Ar and N
_{2}Mixture in RF Discharges at 13.56 MHz. Jpn. J. Appl. Phys.**1994**, 33, 4271–4275. [Google Scholar] [CrossRef] - Fiebrandt, M.; Hillebrand, B.; Spiekermeier, S.; Bibinov, N.; Boke, M.; Awakowicz, P. Measurement of Ar resonance and metastable level number densities in argon containing plasmas. J. Phys. D Appl. Phys.
**2017**, 50, 355202. [Google Scholar] [CrossRef] - Britun, N.; Gaillard, M.; Ricard, A.; Kim, Y.M.; Kim, K.S.; Han, J.G. Determination of the vibrational, rotational and electron temperatures in N
_{2}and Ar–N_{2}rf discharge. J. Phys. D Appl. Phys.**2007**, 40, 1022–1029. [Google Scholar] [CrossRef] - Moravej, M.; Yang, X.; Barankin, M.; Penelon, J.; Babayan, S.E.; Hicks, R.F. Properties of an atmospheric pressure radio-frequency argon and nitrogen plasma. Plasma Sources Sci. Technol.
**2006**, 15, 204–210. [Google Scholar] [CrossRef] - Fritsche, B.; Chevolleau, T.; Kourtev, J.; Kolitsch, A.; Möller, W. Plasma diagnostic of an RF magnetron Ar/N
_{2}discharge. Vacuum**2003**, 69, 139–145. [Google Scholar] [CrossRef] - Kim, Y.-C.; Lee, H.-C.; Kim, Y.-S.; Chung, C.-W. Correlation between vibrational temperature of N
_{2}and plasma parameters in inductively coupled Ar/N_{2}plasmas. Phys. Plasmas**2015**, 22, 083512. [Google Scholar] [CrossRef] - Bravo, J.A.; Rincón, R.; Muñoz, J.; Sánchez, A.; Calzada, M.D. Spectroscopic characterization of argon–nitrogen surface-wave discharges in dielectric tubes at atmospheric pressure. Plasma Chem. Plasma Process.
**2015**, 35, 993–1014. [Google Scholar] [CrossRef] - Becker, K.H.; Masoud, N.M.; Martus, K.E.; Schoenbach, K.H. Electron-driven processes in high-pressure plasmas. Eur. Phys. J. D
**2005**, 35, 279–297. [Google Scholar] [CrossRef] - Barkhordari, A.; Ganjovi, A.; Mirzaei, I.; Falahat, A.; Rostami Ravari, M.N. A pulsed plasma jet with the various Ar/N
_{2}mixtures. J. Theor. Appl. Phys.**2017**, 11, 301–312. [Google Scholar] [CrossRef] - Masoud, N.; Martus, K.; Becker, K. VUV emission from a cylindrical dielectric barrier discharge in Ar and in Ar/N
_{2}and Ar/air mixtures. J. Phys. D Appl. Phys.**2005**, 38, 1674–1683. [Google Scholar] [CrossRef] - Kimura, T.; Akatsuka, K.; Ohe, K. Experimental and theoretical investigations of DC glow discharges in argon-nitrogen mixtures. J. Phys. D Appl. Phys.
**1994**, 27, 1664–1671. [Google Scholar] [CrossRef] - Ionikh, Y.Z.; Meshchanov, A.V.; Petrov, F.B.; Dyatko, N.A.; Napartovich, A.P. Partially constricted glow discharge in an argon–nitrogen mixture. Plasma Phys. Rep.
**2008**, 34, 867–878. [Google Scholar] [CrossRef] - Ionikh, Y.Z.; Dyatko, N.A.; Meshchanov, A.V.; Napartovich, A.P.; Petrov, F.B. Partial constriction in a glow discharge in argon with nitrogen admixture. Plasma Sources Sci. Technol.
**2012**, 21, 055008. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Meshchanov, A.V.; Napartovich, A.P.; Barzilovich, K.A. Specific features of the current–voltage characteristics of diffuse glow discharges in Ar:N
_{2}mixtures. Plasma Phys. Rep.**2010**, 36, 1040–1064. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Meshchanov, A.V.; Napartovich, A.P. Theoretical and experimental study of the influence of nitrogen admixture on characteristics of dc diffuse glow discharge in rare gases at intermediate pressures. J. Phys. D Appl. Phys.
**2013**, 46, 355202. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Meshchanov, A.V.; Napartovich, A.P. Steady-state partially constricted glow discharge. IEEE Trans. Plasma Sci.
**2011**, 39, 2532–2533. [Google Scholar] [CrossRef] - Dyatko, N.; Napartovich, A. Ionization mechanisms in Ar:N
_{2}glow discharge at elevated pressures. In Proceedings of the 41st Plasmadynamics and Lasers Conference, Chicago, IL, USA, 28 June–1 July 2010. Paper AIAA 2010-4884. [Google Scholar] - Isola, L.M.; López, M.; Cruceño, J.M.; Gómez, B.J. Measurement of the Ar(1sy) state densities by two OES methods in Ar–N
_{2}discharges. Plasma Sources Sci. Technol.**2014**, 23, 015014. [Google Scholar] [CrossRef] - Reyes, P.G.; Torres, C.; Martinez, H. Electron temperature and ion density measurements in a glow discharge of an Ar–N
_{2}mixture. Radiat. Eff. Defects Solids**2014**, 169, 285–292. [Google Scholar] [CrossRef] - Zhovtyansky, V.A.; Anisimova, O.V. Kinetis of plasma chemical reactions producing nitrogen atoms in the glow discharge in a nitrogen-argon gas mixturte. J. Phys.
**2014**, 59, 1155–1163. [Google Scholar] - Bogaerts, A. Hybrid Monte Carlo-Fluid model for studying the effects of nitrogen addition to argon glow discharges. Spectrochim. Acta Part B
**2009**, 64, 126–140. [Google Scholar] [CrossRef] - Jackson, G.P.; King, F.L. Probing excitation/ionization processes in millisecond-pulsed glow discharges in argon through the addition of nitrogen. Spectrochim. Acta Part B
**2003**, 58, 185–209. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Meshchanov, A.V.; Napartovich, A.P. Influence of a nitrogen admixture on the anomalous memory effect in the breakdown of low-pressure argon in a long discharge tube. Plasma Phys. Rep.
**2018**, 44, 334–344. [Google Scholar] [CrossRef] - Qayyum, A.; Zeb, S.; Naveed, M.A.; Rehman, N.U.; Ghauri, S.A.; Zakaullah, M.J. Optical emission spectroscopy of Ar–N
_{2}mixture plasma. J. Quant. Spectrosc. Radiat. Transf.**2007**, 107, 361–371. [Google Scholar] [CrossRef] - Martens, T.; Bogaerts, A.; Brok, W.J.M.; Dijk, J.V. The dominant role of impurities in the composition of high pressure noble gas plasmas. Appl. Phys. Lett.
**2008**, 92, 041504. [Google Scholar] [CrossRef] [Green Version] - Wang, Y.; Wang, D. Influence of impurities on the uniform atmospheric-pressure discharge in helium. Phys. Plasmas
**2005**, 12, 023503. [Google Scholar] [CrossRef] - Sasaki, N.; Shoji, M.; Uchida, Y. Capacitively Coupled RF Discharge Breakdown in Gas Mixtures. IEEJ Trans. Fundam. Mater.
**2007**, 127, 714–718. [Google Scholar] [CrossRef] [Green Version] - Zhiglinskii, A.G. (Ed.) Handbook of Constants for Elementary Atomic, Ionic, Electronic, and Photonic Processes; PGU: St. Petersburg, Russia, 1994. (In Russian) [Google Scholar]
- Raizer, Y.P. Gas Discharge Physics; Nauka: Moscow, Russia, 1987; Springer: Berlin, Germany, 1991. [Google Scholar]
- Ionikh, Y.Z.; Chernysheva, N.V. Radiation of gas-discharge plasma in mixtures of inert and molecular gases. In Encyclopedia of Low Temperature Plasma; Fortov, V.E., Ed.; Fizmatlit: Moscow, Russia, 2008; Series B; Volume III 2, pp. 427–443. (In Russian) [Google Scholar]
- Dyatko, N.A.; Ionikh, Y.Z.; Meshchanov, A.V.; Napartovich, A.P.; Petrov, F.B. Volt-ampere characteristics of the partially constricted glow discharge in Ar:N
_{2}mixtures. In Proceedings of the XIX European Sectional Conference on Atomic and Molecular Physics of Ionized Gases, Granada, Spain, 15–19 July 2008; Poster 2.36. Available online: http://www.escampig2008.csic.es/PosterSessions/135.pdf (accessed on 19 January 2019). - Yalin, A.P.; Ionikh, Y.Z.; Miles, R.B. Gas temperature measurements in weakly ionized glow discharges with filtered Rayleigh scattering. Appl. Opt.
**2002**, 41, 3753–3762. [Google Scholar] [CrossRef] - Mnatskanyan, A.K.; Naidis, G.V. Processes of production and loss of charged particles in a nitrogen-oxygen plasma. In Plasma Chemistry; Smirnov, B.M., Ed.; Energoatomizdat: Moscow, Russia, 1987; Volume 14, pp. 227–255. (In Russian) [Google Scholar]
- Berdichevskii, M.G.; Marusin, V.V. Nonequilibrium and ionization mechanism of the nitrogen plasma of an electrodeless RF capacitive discharge at medium pressures. Proc. Sib. Branch USSR Acad. Sci.
**1979**, 8, 72–79. (In Russian) [Google Scholar] - Popov, N.A. Associative ionization reactions involving excited atoms in nitrogen plasma. Plasma Phys. Rep.
**2009**, 35, 436–449. [Google Scholar] [CrossRef] - Guerra, V.; Loureiro, J. Electron and heavy particle kinetics in a low-pressure nitrogen glow discharge. Plasma Sources Sci. Technol.
**1997**, 6, 361–372. [Google Scholar] [CrossRef] - Capitelli, M.; Colonna, G.; De Pascale, O.; Gorse, C.; Hassouni, K.; Longo, S. Electron energy distribution functions and second kind collisions. Plasma Sources Sci. Technol.
**2009**, 18, 014014. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Kolokolov, N.B.; Meshchanov, A.V.; Napartovich, A.P. Experimental and theoretical studies of the electron temperature in nitrogen afterglow. IEEE Trans. Plasma Sci.
**2003**, 31, 553–563. [Google Scholar] [CrossRef] - Dilecce, G.; Benedictis, S.D. Relaxation of the electron energy in the post-discharge of an He-N
_{2}mixture. Plasma Sources Sci. Technol.**1993**, 2, 119–122. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Kolokolov, N.B.; Meshchanov, A.V.; Napartovich, A.P. Jumps and bi-stabilities in electron energy distribution in Ar–N
_{2}post discharge plasma. J. Phys. D Appl. Phys.**2000**, 33, 2010–2018. [Google Scholar] [CrossRef] - Dyatko, N.A.; Napartovich, A.P. Theoretical Study of Plasma Parameters in a dc Glow Discharge and Postdischarge in Argon-nitrogen Mixtures. In Proceedings of the 23rd Europhysics Conference on Atomic and Molecular Physics of Ionized Gases, Bratislava, Slovakia, 12–16 July 2016; EPS ECA (Europhysics Conference Abstracts). European Physical Society: Bratislava, Slovakia, 2016; p. 109. [Google Scholar]
- Hübner, S.; Palomares, J.M.; Carbone, E.A.D.; van der Mullen, J.J.A.M. A power pulsed low-pressure argon microwave plasma investigated by Thomson scattering: Evidence for molecular assisted recombination. J. Phys. D Appl. Phys.
**2012**, 45, 055203. [Google Scholar] [CrossRef] - Golubovskii, Y.B.; Nekuchaev, V.; Gorchakov, S.; Uhrlandt, D. Contraction of the positive column of discharges in noble gases. Plasma Sources Sci. Technol.
**2011**, 20, 053002. [Google Scholar] [CrossRef] - Dyatko, N.A.; Ionikh, Y.Z.; Kochetov, I.V.; Marinov, D.L.; Meschanov, A.V.; Napartovich, A.P.; Petrov, F.B.; Starostin, S.A. Experimental and theoretical study of the transition between diffuse and contracted forms of the glow discharge in argon. J. Phys. D Appl. Phys.
**2008**, 41, 055204. [Google Scholar] [CrossRef]

**Figure 1.**Current–voltage characteristic of discharges in pure argon and the Ar/N

_{2}mixtures at gas pressure P = 2 Torr [33].

**Figure 3.**Calculated (curves) and measured (symbols) dependences of the electric field in the positive columns of discharges in pure argon and the Ar + 1%N

_{2}mixture on the discharge current for P = 2 Torr and 40 Torr [17].

**Figure 4.**Gas temperature at the axis of the discharge tube calculated in pure argon and the Ar + 1%N

_{2}mixture for P = 2 Torr and 40 Torr [17].

**Figure 5.**Ar + 1%N

_{2}. Calculated vibrational distribution functions in discharge (t = 0) and afterglow (t > 0) plasma [44]. R = 1.5 cm, P = 5 Torr, T

_{gas}= 350 K, I = 20 mA.

**Figure 6.**Calculated effective electron temperature in a dc discharge in the Ar + 1%N

_{2}mixture (t < 0) and its time evolution in the discharge afterglow (t > 0). R = 1.4 cm, I = 20 mA. P = 1 Torr (1), 2 Torr (2), and 5 Torr (3) [26].

**Figure 7.**Calculated electron densities in the discharge (t ≤ 0) and in the afterglow (t > 0) at a discharge current of I = 20 mA and gas pressures of P = 1 (

**a**), 2 (

**b**), and 5 Torr (

**c**), respectively [26].

**Figure 8.**Volt-amp characteristic of the discharge under constriction [47]. (© IOP Publishing. Reproduced with permission. All rights reserved.)

**Figure 9.**Volt–amp characteristics of a glow discharge in pure argon and in argon with nitrogen admixture. Percentages of admixture are indicated [16]. (© IOP Publishing. Reproduced with permission. All rights reserved.)

**Figure 10.**Volt–amp characteristics for Ar and Ar-N

_{2}mixture in a region of constricting [16]. (© IOP Publishing. Reproduced with permission. All rights reserved.)

**Figure 11.**Volt–amp characteristic recorded at lowering (from point A) and increasing (from B) of power supply voltage [16]. (© IOP Publishing. Reproduced with permission. All rights reserved.)

**Figure 12.**Steady-state partially constricted glow discharge in the Ar + 0.075%N

_{2}mixture, P = 40 Torr [19] (© 2011 IEEE).

**Figure 13.**Two upper panels are the photos of the transition region between diffuse and constricted parts of discharge. The lower panel is a 120 μs exposure CMOS camera image. In all cases, the cathode is on the left. Ar + 0.075%, P = 80 Torr [19] (© 2011 IEEE).

**Figure 14.**Manifold of PCD points (open squares) for the discharge in the Ar + 0.02%N

_{2}mixture at P = 50 Torr [16]. (© IOP Publishing. Reproduced with permission. All rights reserved.)

**Table 1.**Ar + 1%N

_{2}. Calculated ‘local’ vibrational temperatures (T

_{v}

^{i,i+1}, see comments in the text) and effective electron temperatures (T

_{e}), in discharge (t = 0) and afterglow (t > 0) plasma [44]. R = 1.5 cm, P = 5 Torr, T

_{gas}= 350 K, I = 20 mA.

Discharge | Afterglow | |||
---|---|---|---|---|

t = 0 | 10 ms | 30 ms | 50 ms | |

T_{v}^{0,1}, K | 10,580 | 6300 | 4110 | 3300 |

T_{v}^{1,2}, K | 17,260 | 9150 | 6350 | 5100 |

T_{v}^{2,3}, K | 16,560 | 9990 | 7900 | 6760 |

T_{v}^{3,4}, K | 14,980 | 10,530 | 9410 | 8610 |

T_{v}^{4,5}, K | 9560 | 10,190 | 10,070 | 9870 |

T_{e}, K | 28,900 | 8520 | 6590 | 6050 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Dyatko, N.A.; Ionikh, Y.Z.; Napartovich, A.P.
Influence of Nitrogen Admixture on Plasma Characteristics in a dc Argon Glow Discharge and in Afterglow. *Atoms* **2019**, *7*, 13.
https://doi.org/10.3390/atoms7010013

**AMA Style**

Dyatko NA, Ionikh YZ, Napartovich AP.
Influence of Nitrogen Admixture on Plasma Characteristics in a dc Argon Glow Discharge and in Afterglow. *Atoms*. 2019; 7(1):13.
https://doi.org/10.3390/atoms7010013

**Chicago/Turabian Style**

Dyatko, Nikolay A., Yury Z. Ionikh, and Anatoly P. Napartovich.
2019. "Influence of Nitrogen Admixture on Plasma Characteristics in a dc Argon Glow Discharge and in Afterglow" *Atoms* 7, no. 1: 13.
https://doi.org/10.3390/atoms7010013