DC normal glow discharges in atmospheric pressure atomic and molecular gases

Abstract

DC glow discharges were experimentally investigated in atmospheric pressure helium, argon, hydrogen, nitrogen and air. The discharges were characterized by visualization of the discharges and voltage and current measurements for current of up to several milliamperes. Significant differences are seen in the gas temperature; however all the discharges appear to operate as temperature and pressure scaled versions of low pressure discharges. In the normal glow discharges, features such as negative glow, Faraday dark space and positive column regions are clearly observable. In hydrogen and to a lesser degree in helium and argon standing striations of the positive column were visible in the normal glow regime. Normal glow characteristics such as normal current density at the cathode and constant electric field in the positive column are observed although there are some unexplained effects. The emission spectra for each of the discharges were studied. Also the rotational and vibrational temperature of the discharges were measured by adding trace amounts of N 2 to the discharge gas and comparing modeled optical emission spectra of the N 2 2nd positive system with spectroscopic measurements from the discharge. The gas temperatures for a 3.5 mA normal glow discharge were around 420 K, 680 K, 750 K, 890 K and 1320 K in helium, argon, hydrogen, nitrogen and air, respectively. Measured vibrational and excitation temperatures indicate non-thermal discharge operation. Mixtures of gases achieved intermediate temperatures.

Study of the Influence of Variation in Distances Between Electrodes in Spectral DBD Plasma Excitation

“…Therefore, a parameter that provides an indication of active species density per energy consumed can be very important in evaluating the performance efficiency of a DBD device. Since the major species for air atmospheric discharge are in the range of 300 nm to 420 nm, corresponding to N 2 spectra lines (C 3 Π u -B 3 Π g ) 14 , the integral spectra intensity can be provided by the value in equation 1 15,16 , obtained from the area under the curve shown in Figure 3 (d-e). As such, the I s /E el ratio provides the DBD reactor efficiency in active plasma species production.…”

LIF spectroscopy of OH radicals in a micro-flow DC discharge in Ar and He with a liquid electrode

“…The micro-flow discharge above water surface is one of the examples of plasma in contact with liquid where composition of gas phase can be controlled by external flow of feed gas. Several groups performed a study of the micro-flow atmospheric pressure glow discharge with liquid electrodes in various gases [2,3]. However, the study is mainly focused on electric characteristics and optical emission spectra, while the density of OH, as the most important active species, has not been measured.…”

Comparison of the characteristics of atmospheric pressure plasma jets using different working gases and applications to plasma-cancer cell interactions

“…[33][34][35] The excitation temperatures of He or Ar lines were measured by using the Boltzmann plot -method. [36][37][38] The atomic emission intensity (I pq ) of the transition from level p to level q depends on the transition probability (A pq ) and absolute population of the atomic level (n p ), as shown in the following equation; I pq = n p A pq hν(where h is the Planck constant and ν is the photon frequency corresponding to the p→q transition). Assuming a Boltzmann distribution of the population of the atomic level, the emission intensity is expressed as I pq ∝ A pq g p hν exp − E p k B T exc (where Ep and gp are the energy and degeneracy, respectively, of excited level p, kB is the Boltzmann constant, and Texc is the excitation temperature in Kelvin).…”