Hello.
As the title said, I really want to know the specific reason why ICP simulation (espcially using COMSOL) typically consider only 1st excited state in Argon plasma?
As listed in the attached image, there are a lot of excited states in Ar and each has its only cross section. Considering only single excited state can give underestimated number of excited neutrals, so electron density also has lower value than what it really is.
I firstly thought that maybe higher excited states have very fast decay time or much smaller cross section so they can be ignored. However, NIST data shows that energy differences between 1st and higher excited states are small so maybe they all have similar decay time and cross section. If it is true, then...taking only 1st excited state is big mistake.
I have to answer this question in order to say whether or not my simulation result is right.
Could you please clearify this?
First excited state of Ar is a metastable state, therefore it lives for long time. The other states decay radiativell, therefore their contribution is less important.
To estimate exactly the contribution of all the excited states you need an accurate collisional radiative model.
I usually consider the first excited state.
Perhaps the temperature considered is important. See fig 4 of following.
http://james-keck-memorial-collection.unibs.it/JCKeck-papers/EisazadehFarMetghalchiKeck-JEnergyResTechnol-133-2011.pdf
Cheers
First excited state of Ar is a metastable state, therefore it lives for long time. The other states decay radiativell, therefore their contribution is less important.
To estimate exactly the contribution of all the excited states you need an accurate collisional radiative model.
I usually consider the first excited state.
Thanks to reply this, Gianpiero. You have always answered with good comments:
My concern is this: Although other excited states are radiatively decayed, their lifetime may not be very fast compared with ICP powe frequency of 13.56 MHz as I'm using. And there are very large amount of excited states which all has potential for two step-ionization. So..I really want to know how much contribution to ionization is made by these things. I'm assuming electron temperature of few eV. Could you tell me any comment about this?
At least I agree that another simulation such as collisional radiative model is required to answer this completely and this may be my future work.
you can lump other states (with their cross-sections) into an efficient level to take into account the energy loss of the fast electrons. This energy loss is ultimately responsible for the plasma radiation. See, for example,
https://www.researchgate.net/publication/238020064_Comparison_of_spatially-resolved_experimental_and_calculated_electron_disctribution_functions_and_other_plasma_parameters_in_inductively_coupled_argon_plasma
Article Comparison of spatially-resolved experimental and calculated...
@Donggyu Jang: The 4p states have indeed relatively large cross sections for excitation from the ground state. They can therefore contribute to stepwise ionization processes and increase the total ionization rate. You need however sufficiently high electron densities so that the 4p states are ionized by collisions before they decay radiatively. Nevertheless, if they decay radiatively (i.e. towards 4s states), they will also increase the population densities of the 4s states. If excitation from ground state to 4p states is comparable to excitation from ground state to 4s states (that depends of the EEDF shape), then 4p states cannot be indeed neglected to obtain a correct total ionization rate.
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