Development of asymmetric double probe formula and its application for collisional plasmas

Abstract

The ratio of the electron and ion saturation currents in single probe I-V characteristics for microwave-sustained plasma jets at atmospheric pressure are found to be much smaller than the value expected from the standard high-pressure single probe theory providing an over estimation of electron temperatures. By assuming that the single probe characteristic behaves as an asymmetric double probe when the electron to ion saturation current ratio is reduced, the whole characteristics may be fitted and significantly lower electron temperatures may be derived. In this study, asymmetric double probe theory for collisional plasmas is developed and employed to microwave-sustained helium plasma jets in order to estimate the plasma parameters (electron temperature and plasma density) at atmospheric pressure avoiding the overestimation of electron temperature.

Estimation of Plasma Parameters for Microwave‐Sustained Ar/He Plasma Jets at Atmospheric Pressure

“…From these figures it is observed that the temperature estimated by ADP theory [16,17] decreases with increasing the probe position from the nozzle head for both the gas species as expected, which is the opposite pattern getting from the HSP theory [15] ensuring the reliable plasma parameters estimated by ADP theory [16,17]. The electron temperature estimated by the ADP theory [16,17] is found to be in the range of 1.2∼1.5 eV in the case of Ar plasmas while 0.9∼3 eV in the case of He plasmas indicating that ADP theory provides more reasonable values of plasma parameters. Figure 7 shows the comparison of electron density, N e of He plasma jet estimated by HSP theory [15] and ADP theory [16,17] under the quasi-neutrality condition N e = N i , where N i is the ion density.…”

“…Finally, in order to overcome the limitations of HSP theory [15], we analyze the measured probe characteristics using the recently developed asymmetric double probe (ADP) theory [16,17], and compare the plasma parameters with those estimated by single probe theory [15]. The axial profile of electron temperature, T e of Ar and He plasmas estimated by HSP [15] and ADP theory [16,17] are compared in Fig.…”

“…The axial profile of electron temperature, T e of Ar and He plasmas estimated by HSP [15] and ADP theory [16,17] are compared in Fig. 6(a) and 6(b), respectively.…”

“…An electrostatic probe characteristic using single probe in a dense, partially ionized plasma is studied by Su et al [13] and Cohen [14], and some formulae are introduced by Talukder et al [15], which can easily be applied to single probe diagnosis in order to obtain the plasma parameters by fitting the equation to measured probe data. Recently, an asymmetric double probe (ADP) theory is proposed by our group (Saito et al [16,17]) by extending the Cohen's theory to obtain the plasma parameters at atmospheric pressure. In this work, first, we have analyzed the measured probe characteristics of microwave plasma jets at atmospheric pressure using the high-pressure single probe (HSP) theory [15] in order to determine the generated plasma parameters (electron temperature, T e and electron density, N e ), and then the measured probe characteristics are analyzed by using the recently developed ADP theory [16,17] in order to compare the plasma parameters with those estimated by HSP theory [15].…”

“…Recently, an asymmetric double probe (ADP) theory is proposed by our group (Saito et al [16,17]) by extending the Cohen's theory to obtain the plasma parameters at atmospheric pressure. In this work, first, we have analyzed the measured probe characteristics of microwave plasma jets at atmospheric pressure using the high-pressure single probe (HSP) theory [15] in order to determine the generated plasma parameters (electron temperature, T e and electron density, N e ), and then the measured probe characteristics are analyzed by using the recently developed ADP theory [16,17] in order to compare the plasma parameters with those estimated by HSP theory [15].…”