I have a plasma jet with He as a working gas. I would like measure the electron temperature and electron density by optical emission spectroscopy without using H in plasma jet. I know that I can do this by measuring Stark broadening of the Balmer H line. How can do it?
Dear,
Below is a very interesting article on the subject :
''Diagnosis of gas temperature, electron temperature, and electron density in helium atmospheric pressure plasma jet'', Phys. Plasmas 19, 073513 (2012), Zheng-Shi Chang, Guan-Jun Zhang, Xian-Jun Shao and Zeng-Hui Zhang.
Even if you are not adding hydrogen to your plasma gas, it is still present as an impurity in and may be visible in your emission spectra. Hydrogen is also generated from water that is present both as an impurity in the gas and in the atmosphere (if this is an ambient plasma jet). That would allow you to do the Stark broadening calculations without adding anything to your gas.
Hi,
the Stark broadening will give you the electron density, not Te. Obtaining the temperature correctly will depend mostly on the nature of your jet - if it is a non-thermal plasma source the usually used Boltzmann plot method may give you erroneous results as the species are most likely not in thermodynamical equilibrium. If you have a thermal jet, your can nicely draw your Boltzmann plots.
In case of a non-thermal plasma you can approximate the neutral gas temperature by the rotational temperature of residual OH radicals in your plasma. The electron temperature can then be estimated as pointed out in the paper mentioned by Hssaïne Amamou.
You can use the visible emission of pashen-alpha line of the first ionized Helium to compute the density and the temperature of the electrons.
You can use the visible emission of pashen-alpha line of the first ionized Helium to compute the density and the temperature of the electrons.
@Mohammed Tayeb Meftah
First of all there is no visible emission when it comes to Pashen lines as they are all located in the infrared, secondly, as I said the determination of the electron temperature is very tricky when you are dealing with a non-equilibrium plasma jet (which is very often the case in atmospheric pressure sources).
Depending on the type of plasma the electron temperature is calculated> while the electron density calculated from stark broadening method
I share the opinion of my cooleagues. Anyway, Te and ne can measured by electrostatic probes and/or optical emission spectroscopy and/or Interferometry (e.g. Mach Zender Interferometry). However, there the approaches as outlined above and fast tracks by doping the plasma with small amounts of hydrogen in order to use the H-alpha or H-beta lines to directly derive such paramters (see Griem's book).
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