Determination of the neutral gas temperature of nitrogen-containing low-pressure plasmas using a two-temperature model

425

431

The gas temperature in non-equilibrium plasmas is often obtained from the plasma-induced emission by measuring the rotational temperature of a diatomic molecule in its excited state. This is motivated by both tradition and the availability of low budget spectrometers. However, non-thermal plasmas do not automatically guarantee that the rotational distribution in the monitored vibrational level of the diatomic molecule is in equilibrium with the translational (gas) temperature. Often non-Boltzmann rotational molecular spectra are found in non-equilibrium plasmas. The deduction of a gas temperature from these non-thermal distributions must be done with care as clearly the equilibrium between translational and rotational degrees of freedom cannot be achieved. In this contribution different methods and approaches to determine the gas temperature are evaluated and discussed. A detailed analysis of the gas temperature determination from rotational spectra is performed. The physical and chemical background of non-equilibrium rotational population distributions in molecular spectra is discussed and a large range of conditions for which non-equilibrium occurs are identified. Fitting procedures which are used to fit (non-equilibrium) rotational distributions are analyzed in detail. Lastly, recommendations concerning the conditions for which the gas temperatures can be obtained from diatomic spectra are formulated.

Section: Reactionmentioning

confidence: 99%

Gas temperature determination from rotational lines in non-equilibrium plasmas: a review

Bruggeman

Sadeghi

Schram

et al. 2014

425

431

“…In [27,37], a function with a two-temperature Boltzmann rotational distribution was proposed to fit the FNS bands. However, the function with only one temperature Boltzmann rotational distribution produces a suitable fit on our FNS band spectra.…”

Section: Gas Temperature Measurementioning

confidence: 99%

Measurement of the Ar(1s_y) state densities by two OES methods in Ar–N₂discharges

Isola¹,

López²,

Cruceño³

2014

In this work, results from two methods for the determination of the Ar(1s y ) densities are compared in an Ar-N 2 discharge. These methods involve measurements of optical emission spectroscopy (OES). The first method (band method) uses the bands belonging to the N 2 (C → B) second positive system, while the second method (branching fraction method) uses the line intensities corresponding to the Ar(2p x → 1s y ) transitions. These techniques were tested in the negative glow of dc discharge and the results show remarkable agreement.

“…Gas temperature is one of the most important parameters for plasma applications. For discharges with molecular emission bands, such as OH(A-X) and N 2 (C-B), rotational temperatures of these molecules are often applied to estimate the plasma gas temperature by spectra-fitting the experimental emission bands [48,49]. The emission bands of the second positive system of nitrogen N 2 (C 3 u − B 3 g ) at rovibrational transitions at (0-2), (1-3) and (2-4) from 368 to 383 nm are used and simulated by the software Specair to determine the rotational (T rot ) and vibrational (T vib ) temperatures of nitrogen.…”

Section: Global Emission Spectra and Ro-vibrational Temperaturementioning

confidence: 99%

Characterization of an atmospheric helium plasma jet by relative and absolute optical emission spectroscopy

Xiong

Nikiforov

González

et al. 2012

116

The characteristics of plasma temperatures (gas temperature and electron excitation temperature) and electron density in a pulsed-dc excited atmospheric helium plasma jet are studied by relative and absolute optical emission spectroscopy (OES). High-resolution OES is performed for the helium and hydrogen lines for the determination of electron density through the Stark broadening mechanism. A superposition fitting method composed of two component profiles corresponding to two different electron densities is developed to fit the investigated lines. Electron densities of the orders of magnitude of 10 21 and 10 20 m −3 are characterized for the center and edge regions in the jet discharge when the applied voltage is higher than 13.0 kV. The atomic state distribution function (ASDF) of helium demonstrates that the discharge deviates from the Boltzmann-Saha equilibrium state, especially for the helium lower levels, which are significantly overpopulated. Local electron excitation temperatures T 13 and T spec corresponding to the lower and upper parts of the helium ASDF are defined and found to range from 1.2 eV to 1.4 eV and 0.2 eV to 0.3 eV, respectively. A comparative analysis shows that the Saha balance is valid in the discharge for helium atoms at high excited states.