Measurement of electron temperature in an E x B Penning source by optical emission spectroscopy

E x B discharges are known to exhibit strong low frequency oscillations such as breathing oscillations and rotating spokes.[i] There is a strong interest and need for the characterization of these oscillations and their effect on the plasma using minimum-invasive and non-invasive diagnostics. In this work, we performed high resolution emission spectroscopy to obtain the spatially resolved electron temperature in the plasma generated in an E x B Penning source. We used the line ratio of the emission from the Ar (3p₅ --> 1s₄) and Ar (3p₉ --> 1s₅) lines at 419.83 nm and 420.07 nm respectively to obtain the electron temperature. This ratio depends on the electron temperature and the ratio of the Ar (1s₅) metastable density and the ground state Ar density.[ii] The Ar metastable density was obtained using absorption spectroscopy and the ground state Ar density was obtained from the pressure of the chamber.[iii] The obtained electron temperature was validated using Langmuir probe measurements. The obtained trends of the electron temperature measured with OES are consistent with that measured with the probes.

 

[i] E. Rodriguez, V. Skoutnev, Y. Raitses, A. Powis, I. Kaganovich, and A. Smolyakov, Phys. Plasmas 26, 053503 (2019)

[ii] J. B. Boffard, R. O. Jung, C. C. Lin, L. E. Aneskavich, and A. E. Wendt, J. Phys. D: Appl. Phys., 45(4), 045201 (2012).

[iii] J. B. Boffard, R. O. Jung, C. C. Lin, and A. E. Wendt, Plasma Sources Sci. and Technol., 18(3), 035017 (2009).