# Determination of electron temperature in an ion source

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• HeavyIon
In summary, the Saha equation cannot be used to determine the temperature of electrons in an ion source based on ECR due to the low electron density in these sources. A direct measurement using a Langmuir probe is a better method for determining the electron temperature.
HeavyIon
How to correctly determine the temperature of electrons in an ion source based on ECR?
Is it possible to use the Saha equation?
##\frac{n_en_i}{n_a}=\frac{g_eg_i}{g_a}*3*10^{21} T^{3/2} e^{-J/T}##
Using the search, I found the McWhirter criterion for the applicability of the formula above:
##n_e >>1.6*10^{12}T^{1/2}*\Delta E^3##
Here ##n_e## is the electron density in ##cm^{-3}##, T is the electron temperature in ##eV##, and ##\Delta E## is the largest energy gap between upper and lower energy states that corresponds to one of the spectral lines used. I don't quite understand what \Delta E value should be considered in my case? I'm getting singly charged helium.

Unfortunately, the Saha equation is not applicable to determine the temperature of electrons in an ion source based on ECR. The McWhirter criterion mentioned above indicates that this equation can only be used for electron densities larger than 1.6x10^12 cm^-3. This is usually not the case in ECR ion sources where the electron density is much lower than this threshold. A more appropriate method for determining the temperature of electrons in an ion source based on ECR is to measure the electron energy distribution directly using a Langmuir probe or other similar device. This allows for a more accurate measurement of the electron temperature, rather than relying on the theoretical model of the Saha equation.

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