DC microdischarges in atmospheric pressure helium, argon, nitrogen and air in
the current range from microamps up to amperes
V.I. Arkhipenko, A.A.Kirillov, Ya.A. Safronau and L.V. Simonchik
Stepanov Institute of Physics of the NAS of Belarus, ave. Nezavisimostsi 68, 220072 Minsk, Belarus
Among the Atmospheric Pressure Glow Discharges (APGD), microdischarges (MD) have demonstrated
the possibility of generating stable diffuse, non-thermal plasmas with characteristic dimensions in the 0.01–1
mm range. The unique properties and several selected applications of microplasmas are discussed in review
article [1]. A number of configurations and microplasma devices including coaxial cathode and anode
microcavities, spirals or slits in the cathode and/or anode, etc. have been developed in the past decade. We
will focus on DC MDs at atmospheric pressure. As an example of the cathode boundary layer
microdischarge, Stark and Schoenbach [2] used a micro hollow cathode with dimensions of several hundred
microns. Another example of DC MD is the glow microdischarge investigated in [3] between a planar
cathode and a wire end, separated by a distance on the order of 0.4 mm in free space in different atmospheric
pressure gases like helium, argon, hydrogen, nitrogen and air. The third kind of DC MD, dissimilar to these
two in its geometry was presented in [4]. It is the MD between two parallel planar electrodes separated from
each other by a distance of about 0.2 mm. In all these DC MD investigations, the discharge current did not
exceed several milliamps and was larger than 10 mA in isolated experiments. This is quite clear, because the
cathode fall is characterized by high volumetric power densities in the range of tens to hundreds of kWcm−3.
Due to the elevated temperature, the regimes of stable operation for microplasma are often limited to low
currents and simple gas mixtures. The elevated gas temperature can thus pose problems for the application of
such discharges to processes. The small dimensions of the MDs often limit their applications as well.
In [5-6] we presented the results of DC self-sustained normal APGD investigations in helium, argon and
nitrogen over a wide current range and interelectrode gaps up to 10 mm. In this paper, we focus our attention
mostly on the APGD at small interelectrode gaps, comparable with the dimensions of near cathode layers
(cathode fall, negative glow, Faraday dark space), in the current range corresponding to the transition from
normal glow discharge to subnormal (or Townsend) one and ten milliamps. We can characterize this
discharge as microdischarge. Comprehensive electrical and spectroscopic investigations of the DC glow
microdischarges (interelectrode gaps less than 1 mm) in atmospheric pressure helium, argon, nitrogen and air
in the large current range from microamps up to ten amps were performed. Since the electrodes are located a
short distance apart they influence the normal glow discharge structure and its electrical and optical
parameters. It was shown that the positive columns in all gases used in this investigation are constricted.
Two oscillation (pulsing) discharge regimes were revealed in the discharge current range comparable or
less than low-current limit of normal glow discharge. One regime is defined by oscillation between two
normal glow discharges with currents differing by a large factor. The oscillation frequency depends on the
capacitance of the power supply leads, interelectrode gap, discharge current, ballast resistor, etc. In the
second regime the fluctuations at extremely low current are caused by periodical breakdown of the
interelectrode gap when the power supply voltage exceeds the breakdown voltage of an actual gap.
The heat flux from the positive column into the cathode region takes place even at a discharge current of
a few milliamps. Additional heat flux in the cathode region leads to changes in both the gas temperature in
the cathode region and the interelectrode voltage. One should take into account an additional heat flux in the
cathode region in simulation of microdischarges at atmospheric pressure at a discharge current of a few
milliamps when the discharge gap exceeds the cathode fall layer thickness a few times over.
This work was partially supported by the BRFFR under grants F09F-006 and F09-076.
1.
2.
3.
4.
5.
6.
K.H. Becker, K.H. Schoenbach, J.G. Eden, J. Phys. D 39, R55 (2006)
R.H. Stark, K.H. Schoenbach, J. Appl. Phys. 85, 2075 (1999)
D. Staack, B. Farouk, A.F. Gutsol, A.A. Fridman, Plasma Sources Sci. Technol. 17, 025013 (2008)
Q. Wang, I. Koleva, V.M. Donnelly, D.J. Economou, J. Phys. D 38, 1690 (2005)
V.I. Arkhipenko, A.A. Kirillov, Ya.A. Safronau et al, Plasma Sources Sci. Technol. 17 (2008) 045017
V.I. Arkhipenko, A.A. Kirillov, Ya.A. Safronau et al, Plasma Sources Sci. Technol. 18 (2009) 045013