The plasma temperature is usually found to decrease with increasing the gas pressure. Did any one see the opposite behavior in any experiment specially the cold plasma like glow discharge for example? What might be the reasons?
What temperature do you mean? - The electron temperature, the ion temperature or the neutral gas temperature?
These temperatures are not necessarily the same for a given plasma.
Thank you Dr. Johannes for your interest,
I am talking about the electron temperature only, which is measured using single or double Langmuir probe in cold plasma experiment.
OK. Usually the electron temperature goes down with increasing pressure due to the higher collisionality where the electrons undergo inelastic collisions and loose kinetic energy in the process.
Hence I would say that decreasing Te at higher pressure is the normal behavior, but to give better a opinion, I would have to know more details of your experiment - also when you are dealing with langmuir probes you have to be aware that you may see two different electron species in your U-I traces - the slow bulk electron contribution and the fast tail electrons.
the mean electron energy can increase because of deviation from Maxwellian equilibrium (in the case of a depleted EEDF tail). Independently of that for high pressure plasmas, when molecular ions become important (20 mbar and above for argon), the electron temperature increases also to compensate for volume losses due to dissociative recombination. You might find the following paper interesting: https://www.researchgate.net/publication/236885114_Experimental_investigation_of_the_electron_energy_distribution_function_%28EEDF%29_by_Thomson_scattering_and_optical_emission_spectroscopy
Article Experimental investigation of the electron energy distributi...
Thank you so much Dr. Emile and Dr. Johannes.
I think you agree for the same reason which is the compensation of volume due to recombination in higher pressures, which can lead to the the fast electron tail (like a bi-Maxwellian case).
I think this typically my case. It is a pseudo discharge (up to 1 kV anf 50 mA) working in pressure of 1 torr to 15 torr. The calculations of the temperature using Langmuir probe shows a bi-Maxwellian behavior in few cases of the discharge specially when the probe is placed in the region of virtual cathode.
Dr. Abd Al-Halim , as in case of the electrothermal plasma , especially in case of capillary sources, it can happen , as the confined structure limits the volumetric expansion. But the extent of rise in peak ( or avg. ) temperature will depend on the amount of change in the peak ( or avg. ) bulk density . Which intuitively comes from the equation of state.
In order to allow heating the plasma you should shield it by sorrounfding it by a Holraum, as it is done in NIF
You can find Plasma energy losses by Bremsstralhung and Stefan Boltzman at following excel table, "Fisica" sheet equations 042 and 044. You should heat the plasma over calculated losses to heat it.
Data Useful formula and excel tables for plasma physics V05
Hello Gentlemen. Would any of you be able to do a small, easy experiment related to producing plasma and tell me how much energy is produced by the plasma gas?
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