Electron density measurements by Thomson scattering and Stark broadening in nanosecond pulsed CH₄/Ar plasma

Abstract Two independent approaches for electron density ( n e ) measurements, i.e. Thomson scattering and Stark broadening, are compared against each other in a nanosecond pulsed CH 4 /Ar plasma across a range of conditions (60–500 mbar and 0.5%–2.0% CH 4 ). Reasonable agreement is found between the two techniques up to 0.8 µ s after the plasma pulse, when coherent and incoherent scattering features start to simultaneously appear in the Thomson scattering spectrum. After 2.6 µ s, only incoherent scattering remains, resulting in a more accurate estimation of n e compared to Stark broadening, as the latter suffers from a low signal-to-noise ratio. The maximum n e is proportional to the total gas pressure and varies from 7 × 10 22 m −3 at 60 mbar to 1.4 × 10 23 m −3 at 500 mbar, whereas CH 4 admixing was found to lower the n e . The electron temperature ( T e ), estimated from Thomson scattering spectra, rises from ∼18 000 K to 29 600 K (1.55–2.55 eV) with increasing gas pressure, whilst being mostly independent of the CH 4 admixing ratio. This comparison of the two methods provides guidance to the application of Thomson scattering and Stark broadening in nanosecond pulsed plasmas, highlighting the ranges of experimental conditions and time windows where accurate estimations of n e and T e are feasible.