Development of Ionization waves in an Atmospheric‐Pressure Micro‐Plasma Jet

Abstract

Present study investigated the development of ionization waves in an atmospheric-pressure plasma jet. Plasma was ignited by 6 kHz sinusoidal voltage applied to a cylindrical electrode surrounding the 500 μm inner diameter quartz tube and positioned 10 mm upstream from the tube orifice. The plasma current was observed using a plane electrode placed 20 mm downstream from the tube orifice. The spatial development of ionization waves was monitored by registering the optical emission along the axis of the tube. At voltages in range of 5.5 -7.5 kV only one pulse occurred during positive half-period while at higher voltages the number of pulses increased up to 6 -7 per half-period. The development of the first and subsequent pulses during one half-period was essentially different. For the first pulse the sharp rise of optical emission characterizing the front of the ionization wave occurred initially near the high-voltage electrode and moved towards the tube orifice and further in the He jet. The propagation of ionization wave coincided with the rise of the displacement current measured at the plane electrode. For subsequent ionization waves of the same half-period, the emission occurred initially at the tube orifice and the ionization wave developed simultaneously in two directions: towards the high-voltage electrode and towards the end of the jet. The velocity of ionization wave inside the tube was in range of (2. 5 -5.0)·10 4 m/s for first wave and as high as 1.2·10 5 m/s for subsequent waves.

Time Behaviour of Helium Atmospheric Pressure Plasma Jet Electrical and Optical Parameters

“…We were able to point in this way that, for constant flow rate conditions and fixed electrode arrangement, the length of the outside jet depends on the frequency and amplitude of the driving high voltage pulses ( Figure 6). Supplementary, it has been demonstrated in a number of recent studies, that this characteristic dimension of the outside plasma jets in helium is also influenced by the electrodes dimensions and constructive details [40,41], gas flow rate [38,[42][43][44], dielectric tube diameter [45][46][47].…”

Comparison of two cold atmospheric pressure plasma jet configurations in argon

“…It is important to note that, according to visual inspection, the plasma jet did not come into contact with the grounded disc electrode. Furthermore, earlier investigations have shown that the grounded disc had only a minor influence on the jet parameters at the used distances …”

“…The CAPJ II was composed of a high‐voltage cylinder electrode wrapped around the quartz tube (ID = 0.5 mm and OD = 0.54 mm) 10 mm upstream from the tube orifice. A second grounded electrode used for the determination of current pulses was similarly placed 2 cm below the tube orifice as described in previous papers . It is important to note that, according to visual inspection, the plasma jet did not come into contact with the grounded disc electrode.…”

“…The time resolution of the current measurement system was limited by oscilloscope, and it was 112 ns. Electrical characteristics of CAPJ II were recorded with the Tektronix TDS‐540B oscilloscope as described in detail in our previous work . The voltage applied on the electrode was measured by a capacitive voltage divider (1:1270) with a 1:10 Tektronix P6139A probe, while the current was measured by using a low inductance resistor R ≈ 1.3 kΩ (TBO1K3J88).…”

“…However, there is a lack of systematic studies, which would explain the occurrence of repeated ionization waves in CAPJs and connect the number of ionization waves with the configuration of CAPJ and its working parameters. Our earlier studies with a CAPJ ignited in a submillimetre diameter quartz tube with He gas showed that the number of ionization waves increased with the amplitude of applied sinusoidal voltage . The subsequent ionization waves occurred after fixed time delays, and it was proposed that their initiation is controlled by the decay of the volume charge of previous ionization wave.…”