according to Griem's formular, w_s=2×[1+1.75×〖10〗^(-4) N_e^(1⁄4) α×(1-0.068N_e^(1⁄6) T_e^(-1/2) )]〖10〗^(-16) w_e N_e ,so could we use electron excitation temperature obtained by Boltzmann Plot to replace electron temperature in calculation of electron density?
It depends if the plasma is in equilibrium or not. You have many cases.
1) the electron energy distribution is a maxwellian. In this case the meaning of electron temperature is associated to the whole distribution,
2) the electron energy distribution is not a maxwellian. In this case the words "electron temperature" lose their meaning. Usually the low energy distribution is a maxwelian and the electron temperature entering in the Griem formula refers to the temperature describing this part of the distribution. On the other hand, the electronic excitation temperature refer to the distribution above the excitation energy, and therefore it is not correlated to the temperature of the low energy distribution. Therefore, in general, excitation temperature is not related to the stark broadening. By the way, the Griem formula is calculated assuming a maxwellian distribution for the electrons.
However this is only one aspect of the problem. Another aspect is related to electron density. The population of excited states is obtained by the contribution of different processes, electronic excitation/deexcitation, radiative decay/pumping, recombination/ionization. To have that the excitation temperature is related to electron temperature, the dominant process should be excitation/deexcitation by electron impact. On the other hand, radiative processes as well as recombination/ionization are important source of non-equilibrium, therefore, the correlation between electron temperature (also in case of a maxwellian distribution) and electronic temperature is loss.
Using excitation temperature in place of electron temperature is only valid under the assumption that the plasma is in equilibrium. In many cases Texc can still be used as an estimation of Te, knowing that it can be an approximation.
To evaluate the error made in this assumption, a collisional radiative model should be developed.
Dear,
If the conditions (LTE criterion of McWhirter : MCWHIRTER, R. W. P. 1965 Plasma Diagnostic Techniques (ed. R. H. Huddlestone & S. L. Leonard), Academic Press) of a LTE plasma are verified, then you can consider that all the plasma particles are at a same temperature.
First establish that the plasma in in LTE and also optically thin, then the excitation temperature will be the same as plasma temperature. To confirm LTE, there is a minimum electron number density required: ne= 1.6x10^12 (DE)^3. (T)^1.5
so that the collisional excitation dominates the rediative decay.
Aslam
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Electromagnetics