Acta Polytechnica doi:10.14311/AP.2015.55.0059 Acta Polytechnica 55(1):59–63, 2015 © Czech Technical University in Prague, 2015 available online at http://ojs.cvut.cz/ojs/index.php/ap DIFFUSE DBD IN ATMOSPHERIC AIR AT DIFFERENT APPLIED PULSE WIDTHS Ekaterina Shershunova∗, Maxim Malashin, Sergei Moshkunov, Vladislav Khomich Institute for Electrophysics and Electric Power RAS, St. Petersburg, Russia, 191186, Dvortsovaya nab., 18 ∗ corresponding author: eshershunova@gmail.com Abstract. This paper presents the realization and a diagnosis of the volume diffuse dielectric barrier discharge in a 1-mm air gap when high voltage rectangular pulses are applied to the electrodes. A detailed study has been made of the effect of the applied pulse width on the discharge dissipated energy. It has been found experimentally that the energy remained constant when the pulse was elongated from 600 ns to 1 ms. Keywords: dielectric barrier discharg; pulsed power supply; atmospheric pressure; pulse width; pulse energy. 1. Introduction In recent years, much attention has been focused on realizing a diffuse atmospheric dielectric barrier dis- charge (DBD), and on investigating DBD, in associ- ated with its potential for use in plasma medicine, surface treatment, plasma chemistry, etc. Many re- searchers have shown that the diffuse mode of DBD with two discharge peaks per one voltage pulse can be ignited at low pressure, and even at atmospheric pressure, in gases such as neon, argon and helium by applying high voltage pulses with short durations to the electrodes [1, 2]. This increases the energy input into the discharge. There is no power consumption during the secondary discharge. At the same time, the energy stored at the barrier after the primary discharge is consumed. As a rule, diffuse high-current DBD in atmospheric air is realized by applying voltage pulses of submi- crosecond duration to the electrodes. There have been few studies on the influence of applying pulse width on DBD behavior in the microsecond range. In previous works, short bell-shaped pulses were used for initiating diffuse DBD in air [3, 4]. Only one primary discharge Figure 1. Experimental setup for realizing and diagnosing DBD. pulse was clearly observed when applying these pulses. In our work, we present an experimental study, us- ing a specially developed generator, of the influence of the applied pulse width on DBD development in atmospheric air. 2. Experimental Setup A special experimental setup was designed to generate a volume DBD in atmospheric air (Figure 1). Two special semiconductor switches S1 and S2 [5, 6] were used to supply DBD with rectangular voltage pulses with varying parameters: amplitude from 0 to 16 kV, pulse width from 600 ns to 1 ms, pulse repetition rates 1–3000 Hz. In addition, the rate of the rise of the applied voltage can easily be changed by varying the value of external resistor R1, thereby enabling the DBD mode to be controlled [7, 8]. DBD was initiated in a 1 mm atmospheric air gap (DG) under conditions of natural humidity of 40–60 % between two plane-parallel aluminum electrodes, one of which was covered by a 2 mm alumina ceramic plate at a pulse repetition rate of 30 Hz. The desired pulse width of the applied voltage was set by varying the 59 http://dx.doi.org/10.14311/AP.2015.55.0059 http://ojs.cvut.cz/ojs/index.php/ap E. Shershunova, M. Malashin, S. Moshkunov, V. Khomich Acta Polytechnica Figure 3. Experimental (Vin, It) and calculated (Vdg, Ids) voltage and current traces of the volume diffuse DBD in a 1 mm air gap. Figure 2. Equivalent circuit of DG. time delay between triggering switches S1 and S2. The voltage applied to the electrodes (Vin) was measured using a Tektronics P6015A high-voltage probe, and the total current in DG (It) was measured through the voltage drop at the 50 Ω series low-inductance resistor Rs. The voltage and current waveforms were displayed on a LeCroy WaveRunner oscilloscope (bandwidth 1 GHz, sampling rate 10 GS/s). The measured traces were the result of processing 1000 events. 3. Calculating the electrical and energy characteristics of volume diffuse DBD in atmospheric air The voltage drop for different elements of the dis- charge gap (DG), currents flowing through the circuit, discharge and supply power were evaluated according to the widely-used equivalent electrical circuit of the capacitive divider (Figure 2). The voltage applied to the electrodes Vin and the total current in DG It, corresponding to the sum of the displacement current Ia (in the absence of a dis- charge) and the conduction current Ids, are measured experimentally. From this data it is easy to calculate the voltage for the air gap Vdg and discharge current Ids. The voltage drop of the air gap is found by sub- tracting the voltage drop at the barrier Vb from the applied voltage Vin, using the formula Vdg = Vin − Vb, where Vb = 1Cb ∫ It dt is the voltage at the barrier, It is the total current, and Cb is the capacitance of the barrier. The discharge current is calculated from the dif- ference between the total current and the current through the air capacitor Ca in the absence of the discharge: Ids = It − Ia, where Ca is the capacitance of the air gap. The current through the air capacitor 60 vol. 55 no. 1/2015 Diffuse DBD in Atmospheric Air at Different Applied Pulse Widths Figure 4. Externally supplied power Psup and discharge dissipated power Pds versus time, tp = 600 ns. Figure 5. Temporal dependences of discharge energy Eds and the energy from the external source Esup (Vin = 16 kV, tp = 600 ns, h = 1 mm, air, alumina ceramic barrier). is obtained by multiplying the air capacitance and the time derivative of the voltage across the air gap, i.e., as Ia = Ca dVdg dt . Then, knowing the discharge cur- rent and the voltage at DG, the instantaneous power dissipated in the discharge Pds can be calculated as Pds = IdsVdg. Hence by integrating over time we find the discharge dissipated energy: Eds = ∫ Pds dt. The energy transferred from the external circuit can be estimated by the formula Esup = ∫ Psup dt, where Psup = ItVin. 4. Results Figure 3 presents typical voltage and current wave- forms of the volume diffuse DBD at Vin = 16 kV, f = 30 Hz, R1 = 85 Ω and pulse width tp = 600 ns. As voltage Vin applies to the electrodes of DG, cur- rent It starts to flow through the circuit. Initially, this current charges the equivalent capacitance of DBD, which corresponds to a small hump at current trace It. When the voltage at the air gap Vdg exceeds the breakdown value, the primary discharge ignites. This looks like a sharp peak in the waveform. The situation at the falling voltage edge is similar to the picture at the rising edge. First, the capacity of DBD is recharged, and then, when the breakdown voltage is exceeded, a discharge appears in DG, i.e. in the conduction current, corresponding the secondary discharge pulse. The time-dependences of the externally supplied power Psup and the power dissipated in the discharge Pds are shown in Figure 4. Power comes from the external circuit (Psup) to charge the equivalent capacitance of DBD and to the discharge process (Pds). The secondary discharge pulse appears without direct consumption of power from the external source. This occurs due to the charge stored at the surface of the barrier after the pri- mary discharge passes. The secondary discharge pulse leaves no charges on the barrier after it finishes. The calculated energy released in the primary discharge is about 1.8 mJ, and in the secondary discharge the calculated energy release is 1.5 mJ (Figure 5). Thus, the energy released per one pulse in the volume diffuse 1 mm DBD in air was ∼ 3.3 mJ at the pulse width of the applied voltage of 600 ns. We recorded the voltage and current traces for dif- ferent pulse widths in order to compare the discharges. Figure 6 shows that with the elongation of the applied voltage pulse from 600 ns to 1 ms the peak current of the primary discharge remained constant at ∼ 15 A, but the peak current of the secondary discharge in- creased slightly. According to our experimental data, the charge transferred during the secondary discharge is constant 61 E. Shershunova, M. Malashin, S. Moshkunov, V. Khomich Acta Polytechnica Figure 6. Dependences of primary and secondary discharge peaks versus pulse width. Figure 7. Current It and voltage Vdg traces of the secondary discharge at different pulse widths. with measured accuracy. We also consider the barrier capacitance to be constant. This allows the voltage at the barrier to be considered constant in the no- discharge period of the pulse. The voltage applied to DG Vin decreases due to the leakage current in the circuit, thus having an influence on the gap voltage. The growth of the secondary current pulse can there- fore be explained by an increase in the gap voltage amplitude with pulse elongation (Figure 7). The peak power of the primary discharge was about 150 ± 15 kW at any pulse width (Figure 8). The peak power of the secondary discharge changed twice as the pulse width increased from 600 ns to 1 ms. The total discharge energy in the pulse remained the same for any pulse width from the range. It was equal to 3.3 ± 0.1 mJ, where 1.8 mJ was dissipated in the primary discharge, and 1.5 mJ was dissipated in the secondary discharge. 62 vol. 55 no. 1/2015 Diffuse DBD in Atmospheric Air at Different Applied Pulse Widths Figure 8. Peak discharge power (P1 — primary discharge, P2 — secondary discharge) versus pulse width. 5. Summary The volume diffuse DBD was realized in a 1 mm air gap when supplying the DG with rectangular unipolar voltage pulses 16 kV in amplitude, with a pulse repeti- tion rate of 30 Hz at different pulse widths, from 600 ns to 1 ms. It was found experimentally that there was no correlation between the pulse width of the applied voltage and the energy dissipated in the discharge. The total dissipated discharge energy per pulse was about 3.3 mJ. It was also found that the slump in the applied voltage could cause an increase in the peak power of the secondary discharge. Acknowledgements The research work presented here was funded by the Rus- sian Foundation for Basic Research, grant No. 1308-01043. References [1] Shuhai Liu, Manfred Neiger. Excitation of dielectric barrier discharges by unipolar submicrosecond square pulses. Journal of Physics D: Applied Physics 34(11):1632, 2001. doi:10.1088/0022-3727/34/11/312 [2] XinPei Lu, Mounir Laroussi. Temporal and spatial emission behavior of homogeneous dielectric barrier discharge driven by unipolar sub-microsecond square pulses. Journal of Physics D: Applied Physics 39(6):1127, 2006. doi:10.1088/0022-3727/39/6/018 [3] T. Shao, D. Zhang, Y. Yu, C. Zhang, J. Wang, P. Yang, Y. Zhou. A compact repetitive unipolar nanosecond- pulse generator for dielectric barrier discharge application. IEEE Transactions on Plasma Scienc 38(7):1651-1655, 2010. doi:10.1109/TPS2010.2048724 [4] H. Ayan, G. Fridman, A. F. Gutsol, V. N. Vasilets, A. Fridman, G. Friedman. Nanosecond-pulsed uniform dielectric-barrier discharge. IEEE Transactions on Plasma Science 36(2):504-508, 2008. doi:10.1109/TPS.2008.917947 [5] V.Yu. Khomich, M.V. Malashin, S.I. Moshkunov, I.E. Rebrov, E.A. Shershunova. Solid-state system for Copper Vapor Laser Excitation. EPE Journal 23(4):51–54, 2013. [6] M. V. Malashin, S. I. Moshkunov, I.E. Rebrov, V. Yu. Khomich, E. A. Shershunova. High-voltage Solid-State Switches for Microsecond Pulse Power. Instruments and Experimental Techniques 57(2):140-143, 2014. doi:10.1134/S0020441214010242 [7] E. Shershunova, M. Malashin, S. Moshkunov, V. Khomich. Generation of Homogeneous Dielectric Barrier Discharge in Atmospheric Air without Preionization. Abstract Book of the 19th Int. Vacuum Congress. Paris, France. p. 1242, 2013. http://apps.key4events.com/key4register/images/ client/164/files/Abstracts_IVC19.pdf [2014-12-01]. [8] M. V. Malashin, S. I. Moshkunov, V. Yu. Khomich, E. A. Shershunova, V. A. Yamshchikov. On the possibility of generating volume dielectric barrier discharge in air at atmospheric pressure. Technical Physics Letters 39(3):252-254, 2013. doi:10.1134/S106378501303010 63 http://dx.doi.org/10.1088/0022-3727/34/11/312 http://dx.doi.org/10.1088/0022-3727/39/6/018 http://dx.doi.org/10.1109/TPS2010.2048724 http://dx.doi.org/10.1109/TPS.2008.917947 http://dx.doi.org/10.1134/S0020441214010242 http://apps.key4events.com/key4register/images/client/164/files/Abstracts_IVC19.pdf http://apps.key4events.com/key4register/images/client/164/files/Abstracts_IVC19.pdf http://dx.doi.org/10.1134/S106378501303010 Acta Polytechnica 55(1):59–63, 2015 1 Introduction 2 Experimental Setup 3 Calculating the electrical and energy characteristics of volume diffuse DBD in atmospheric air 4 Results 5 Summary Acknowledgements References