Modified Boltzmann plot is one of the widely accepted method for electron temperature estimation in atmospheric pressure plasma jets. Since, this is based on the relative emission intensities existing in the optical emission spectrum of a particular plasma, I wanted to estimate electron temperature for Argon plasma jet. Using 14 emission lines, I obtained the value of electron temperature around 0.35 eV.
I used the same spectrums to calculate electron temperature using collisional radiative model. The electron temperature is observed to be much higher than obtained using Modified boltzmann plot.
The plots of both methods have been attached here.
Can somebody help me why there is so much variation between the electron temperatures of modified boltzmann plot and collision radiative model although I use same spectrums for calculation ??
Even if you call both quantities electron temperature, you are talking about two different things. It is not clear what you call collisional radiative model approach. I thing that you assume in both cases a Boltzmann distribution for levels and Maxwell distribution for electrons. This assumption is often valid in atmospheric plasmas. In flowing plasma this assumption should be taken carefully, especially for noble gases. The presence of high energy metastable (in argon is about 10 eV) not observable in the emission spectra, is a source of non-equilibrium. Both electron and internal distribution are not Maxwell/Boltzmann and therefore the concept of temperature is misleading.
Look at
Kinetic processes for laser induced plasma diagnostic: A collisional-radiative model approach by LD Pietanza, G Colonna, A De Giacomo, M Capitelli - Spectrochimica Acta Part B: Atomic Spectroscopy, 2010 http://www.sciencedirect.com/science/article/pii/S0584854710000625
and
Boltzmann and master equations for magnetohydrodynamics in weakly ionized gases by G Colonna, M Capitelli - Journal of Thermophysics and Heat Transfer, 2008 http://arc.aiaa.org/doi/abs/10.2514/1.33479
to see examples of non equilibrium distributions.
Typical eedf in post discharge in Ar present a long plateaux up to 10 eV due to the cooperative effect of superelastic (de-excitation of ar by electron impact)
e(E) +Ar* > e(E+E*) +Ar
and elastic collisions.
The Boltzmann plot technique therefore gives you the level temperature, the second one (still and excitation temperature) gives you the temperature of a Boltzmann connecting the zero energy and the emitting level. The difference in temperature shows that you have a plasma in recombination regimes, where the population of the level is not determined only by the excitation from the ground state, but also from recombination e+Ar+, which produces a plateaux also in the level distribution
see for example
Coupled solution of a time-dependent collisional-radiative model and Boltzmann equation for atomic hydrogen plasmas: possible implications with LIBS plasmas
G Colonna, LD Pietanza, M Capitelli - Spectrochimica Acta Part B: Atomic Spectroscopy, 2001 http://www.sciencedirect.com/science/article/pii/S0584854701002233
and the book
M. Capitelli et al. Fundamental Aspects of Plasma Chemical physics: Kinetics
Hope it helps
What do you mean by a modified Boltzmann plot method? What did you include in your collisional radiative model?
In an argon plasma at atmospheric pressure, 2p states densities are strongly redistributed by neutral collisions and their ratios are then only weakly sensitive to the electron temperature and they can then hardly give any information on the electron energy distribution function..
Dear Gianpiero Colonna ,
Thank you so much for your explanation. The collision radiative model assumes that the ground state argon atoms are excited to various 2p states by collisions and emission occurs when they fall to 1si(i=1,3) metastables states. You can find detailed explanation in the article: http://aip.scitation.org/doi/full/10.1063/1.2409318
Still, I could not understand "the level temperature". Does it mean the temperature of 2px excited state ?
Dear Emile A. D. Carbone ,
Thank you too.
You can find the details of modified boltzmann plot here : http://www.trappa.es/sites/trappa.iaa.es/files/vazquez/journal_publications/art31.pdf
I have read many of your papers and I believe you already know this.
In the CR model plot that I showed in the graph, I follow the assumptions of Dr. Mariotti in the article, http://aip.scitation.org/doi/full/10.1063/1.2409318 that the population of the 4p excited argon levels (2p1 – 2p10 in Paschen notation)
mainly occurs by electron collision with argon atoms in the
ground level and with atoms in the metastable levels (1s3 and
1s5 in Paschen notation). I have chosen 2p4, 2p5, 2p7 and 2p8 in order to obtain the values of metastable state densities n1s3 and n1s5. Finally, population density of 2p4 and 2p5 have been plotted and their point of intersection have been taken as the value of electron temperature.
Could you please suggest me the better method for estimating electron temperature in plasma other than this ?
I give a look to the papers. What I call level temperature is what is called excitation temperature in the paper http://aip.scitation.org/doi/full/10.1063/1.2409318.
The main problem is that the distribution is not a Boltzmann, influencing the excitation rate, especially those from the ground state. This mean a wrong estimation of Te and Ne.
Mr. Bhagirath Ghimire
You can find the details of modified boltzmann plot here : http://www.trappa.es/sites/trappa.iaa.es/files/vazquez/journal_publications/art31.pdf
You mentioned the above link in your answer which lead to something wrong by clicking on it.
I need the paper about the detail of modified Boltzmann plot method. If you have this paper please sent me at the following email.
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