Spontaneous emission probabilities for ion ХеII and distribution of excited states in low-temperature plasma of Hall-effect Thruster

Аuthors

Krivoruchko D. D.^*, Kuli-zade M. E.^**, Skorokhod E. P.^***, Skrylev A. V.

Moscow Institute of Physics and Technology (National Research University), 9, Institutskiy per., Dolgoprudny, Moscow region, 141701, Russia

*e-mail: daria.krivoruchko@phystech.edu
**e-mail: kuli_marina@mail.ru
***e-mail: e.p.skorohod@mail.ru

Abstract

Nonequilibrium low-temperature xenon plasma of Hall-effect Thruster (HT) was investigated by spectroscopic measurements in the 250 - 1100 nm range. e Facility and investigation methodology description is discussed in detail in [1]. The problem researched is to find coefficients for all xenon lines using various models and experimental values ​​of the lines intensities, to determine concentrations of excited states (population), to construct distribution of excited states (DES).

Within the framework of the six models the probability calculations including radiative transitions related to the lowest levels are considered. The examined probabilities are tabulated. A comparison is made with the experimentally obtained results of papers [20-21]. Based on the spectrum data, a DES was constructed for each position of the recording equipment: 1) the lens was mounted coaxially with the HET stream and "look" at the center of the channel; 2) the radiation was sel ected by an external lens system perpendicular to the axis of the engine at a distance of 1 cm from the cut; 3) the radiation was taken at an angle of 14 ° to the axis of the HET, starting from the channel cut; 4) - in a different plane, from the position 1 to 12 down.

The distributions for different parts of the plasma jet 1-4 are of the same nature.

For position 2, the distributions were analyzed using the Einstein coefficients calculated with different models. The structure of the DES is sensitive to the choice of the model for calculating the probabilities of radiative transitions. The intermediate type of coupling for the angular dependences of the matrix elements did not lead to the expected result. The DES based on these data had pronounced energy oscillations, what could have been caused by the erroneous determination of the percentage of different states.

The use of the LS- coupling in combination with all three models of calculating radial integrals does not give a wide spread of populations. The DES using experimentally determined Einstein coefficients [20-21]agrees well with the results when the probabilities were calculated in the Hartree-Fock-Slater approximation with the LS- type of coupling.

The concept of a state vector is introduced, as a combination of the distributions of the excited states of an atom with analogous ion distributions. Just as in atomic physics, for each atom, there is a different level scheme (Grotrian) corresponding to the wavelengths of the ruled spectrum, so any plasma has its own "bar code" in the form of individual distributions of excited states of atoms and ions obtained fr om spectra.

Keywords:

Xe plasma, Hall-effect thruster, the probability of photo-transitions of XeII, the distribution of excited states of XeII, optical diagnostics

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