A Computationally Assisted Ar I Emission Line Ratio Technique to Infer Electron Energy Distribution and Determine Other Plasma Parameters in Pulsed Low-Temperature Plasma

Abstract

In the post-transient stage of a 1-Torr pulsed argon discharge, a computationally assisted diagnostic technique is demonstrated for either inferring the electron energy distribution function (EEDF) if the metastable-atom density is known (i.e., measured) or quantitatively determining the metastable-atom density if the EEDF is known. This technique, which can be extended to be applicable to the initial and transient stages of the discharge, is based on the sensitivity of both emission line ratio values to metastable-atom density, on the EEDF, and on correlating the measurements of metastable-atom density, electron density, reduced electric field, and the ratio of emission line pairs (420.1–419.8 nm or 420.1–425.9 nm) for a given expression of the EEDF, as evidenced by the quantitative agreement between the observed emission line ratio and the predicted emission line ratio. Temporal measurement of electron density, metastable-atom density, and reduced electric field are then used to infer the transient behavior of the excitation rates describing electron-atom collision-induced excitation in the pulsed positive column. The changing nature of the EEDF, as it starts off being Druyvesteyn and becomes more Maxwellian later with the increasing electron density, is key to interpreting the correlation and explaining the temporal behavior of the emission line ratio in all stages of the discharge. Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model.

Probing Collisional Plasmas with MCRS: Opportunities and Challenges

“…This means that the spatial profile of the collision frequency greatly influences the obtained νm . Even for low-pressure situations where the collision frequency does not exceed the applied microwave frequency [6], this discrepancy in the outcome for the two definitions might be extremely relevant. For this reason, users of MCRS should hedge concerning the obtained electron collision frequency, even more so concerning the electron temperature as it requires an additional assumption: the type of Electron-Energy Distribution Function (EEDF).…”

“…Since the introduction of Microwave Cavity Resonance Spectroscopy (MCRS) as a plasma diagnostic in the 1940s [1], the technique has been solidified by a series of publications [2][3][4][5]. Over the last eight decades, the measurement approach has been used to study various types of low-pressure plasmas: pristine radio-frequency (RF) driven low-pressure plasmas [6,7], powder-forming plasmas [8][9][10], etching plasmas [11], ultracold plasmas [12], and extreme ultraviolet photon-induced plasmas [13][14][15]. The measurement approach has also been used to determine properties of materials, i.e., dielectric constants [16] and molar polarizations [17].…”

Characterization of cyclic dust growth in a low-pressure, radio-frequency driven argon-hexamethyldisiloxane plasma

“…The free electron density of the plasma was monitored using MCRS. In the past, this method has been applied to various types of plasmas [27,60,[74][75][76][77][78][79]. With this technique, microwaves with a fixed power of P microwave = 40 mW were introduced into the cavity using a vector network analyzer (Keysight E5072A, frequency range 3-8 GHz, temporal resolution ∼100 ms).…”

Resonant microwaves probing acoustic waves from an RF plasma jet

“…Changes in the former relate to differences in the real part of the permittivity, while the latter is coupled to the imaginary part. In the past, MCRS was used to study various types of plasmas: pristine RF driven plasmas [16,17], etching plasmas [18], powder-forming plasmas [19][20][21], ultracold plasmas [14], EUV photon-induced plasmas [22,12], and high voltage pulsed [13] and radio-frequency driven [15] atmospheric-pressure plasma jets. Besides for studying plasmas, this technique has been used to determine properties of materials, i.e.…”