Optical Emission Spectroscopy for Studying the Region of Interaction between a Plasma Flow and a Tungsten Sample

This work proposes methods for processing optical emission spectroscopy data obtained from the interaction region of helium plasma with the main gas concentration [He] ≈ 10¹²–10¹⁴ cm^–3 and electron density ne ≈ 10¹¹–10¹³ cm^–3 with a tungsten sample at the PLM installation created for studying materials under plasma impact. We proposed a method for determining the temperature of the electrons using the coronal approximation. The calculation is performed on spectral lines with intensity ratio most sensitive to electron temperature variation. For our case it is ion-to-atomic line intensity ratio. We have found that relation of experimental intensities of ion line He II 468.5 nm and a number of atom lines He I with well-known electron excitation constants to the calculated values of this relation for the average electron energy is a reliable method of spectroscopic determination of electron temperature of rarefied magnetized helium plasma. For these experiment conditions: helium concentration [He] ≈ 10¹⁴ cm^–3, discharge current 2–10 A, voltage drop 160– 180 V, discharge radius 16 mm and length 370 mm the value of electron temperature found from two singlet and two triplet He I lines was Te = 2.5 ± 0.3 eV. Taking into account nonlocality of electron energy distribution function (EEDF), complex nature of charge drift and diffusion in crossing and inhomogeneous electric and magnetic fields and other phenomena, the average electron energy = (3/2)kTe 3.6 eV matching this temperature can be considered a lower-bound estimate for the energy of the Maxwell region of EEDF of the plasma under study.

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