Hi everybody,
I would like your opinion in the fact that we can consider a weakly ionized gas as a non-thermal plasma in a temperature range 1000 K -1500 K under pressured gas (like SF6 or other)?
Cold plasmas (non-thermal plasma) are those with Te >> Tgas where the discharge is partially ionized Or weakly ionized plasma. It is obtained in low pressure discharges or in short pulse discharges as Dielectric Barrier Discharges or ns discharges.
Hot plasmas, or thermal plasmas, are those with Te~Tgas where the discharge is approximately totally ionized. It is produced in plasma torches or in high pressure discharges. The time of the discharge must be quite long, in order to have equilibrium between the electron gas and heavy particles.
Salam alikum Kamal.
Thank you for your answer.
But I think that there is a difference between cold plasma and non-thermal plasma. the difference between them is the electronic temperature.
Anywhere, my problem is if I have a cylinder not fully ionised or ionised, is the temperature of the plasma in the range 1000 K - 1500 K? Especially with pressured gas.
Wa Alaikom elsalam my Prof.
Which temperature do you mean?
If you mean the electron temperature, it is cold plasma. Te can be up to 10 eV (1eV=11604 K).
All the problem is here. If I can consider that the ionised channel is a cylinder, than the current is the result of the electron flow. So, 1000 K (for example) is Tgas or Te. Let consider for example short streamer discharges. At the front, photo-ionisation is main producer of electrons that flow through the channel and heating the gas. In the literature, this kind of discharge is considered as cold plasma with T
Hi everyone,
Can you please provide more information about how you measure the temperature ?. The electrons temperature is in the order of magnitude of some ~eV (1eV=11605 K). If you are measuring 1000 K of temperarture, that is probably the gas temperature which is
Dear Ayyoub,
I ask the question because I performed a model for surface discharge in pressured gases. In my model, I make an assumption that between the discharge head and the ground electrode, the gap is ionised and can be considered as a non-thermal plasma with a temperature less than 1500 K. I want to be sure that my assumption is acceptable.
i will be happy if you have any comment or suggestion.
Amine
Dear Amine,
Honnestly, I am not able to give a precise answer to your question based on these information. It depends on the configuration, pression, voltage, current, type of discharge (glow, streamer, arc...) ?, is your model a multi-species model or electrostatic model ?
The plasma is an ionized gas that is globally neutral which means that n(-) = n(+), do you think that the neutrality is realized in this region ?
When you say "discharge head", do you mean "streamer's head" ?. If it is the case, the streamer is non-thermal plasma filament characterized by a region of enhanced electric field at its head, if the streamer is propagating from your HV electrode toward the ground electrode, the plasma region is between the HV electode and the streamer's head, not between the streamer's head and the ground electrode.
I think Saha equation may help us.
Given that the temperature is about 1000-1500 K, ionization energy of SF6 is about 13.6 eV on average (of course it may not easily to consider a unique value due to dissociation) and neutral Number density of 10^25 to 10^27 m-3, then the ion number density will be in range between 10^-9 to 10^4 m-3.
This value is very low and I think that the electron number density would be so higher than that in which most the energy may be exhausted by electrons not ions so that Te>>Ti.
How we can resolve this, It may depends on the range at which we define the "cold plasma" or the "thermal plasma". In the present case, simply, the input energy is high enough to ionize the gas to reach a 'plasma' but NOT to push it into thermal case. While for a relatively higher input energy or lower pressure, it will be different. So, we need first to know in which range of pressures we may 'increase or decrease' and how much input energy is applied.
Regards
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Dear Mohamed,
Thank you for your answer. I appreciate it a lot.
The experiments I have done is about flashover of a solid insulator in SF6 media. The range of the applied voltage (lightning impulse 1.2/50 µs) is about 90 - 150 kV. The main observation is that the flashover voltage is not depending on the SF6 pressure as contrary to free volume (without solid insulator). This because maybe the electron emission from the insulator when the discharge burns. Other observations show that during the discharge propagation, two zones are visible; the first one is a streamer/leader discharge starting from the needle and the second one is a low light column between the head of the discharge (in contact with the insulator) and the ground electrode. I deduce that this zone can be considered as plasma with a temperature of less than 1500 K. This the main assumption and I want to be sure that it is acceptable from the physics point of view.
Regards,
Amine