Effect of secondary emission on the argon plasma afterglow with large dust density

Abstract

A zero-dimensional, space-averaged model for argon plasma afterglow with large dust density is developed. In the model, three groups of electrons in the plasma afterglow are assumed: (i) thermal electrons with Maxwellian distribution, (ii) energetic electrons generated by metastable-metastable collisions (metastable pooling), and (iii) secondary electrons generated at collisions of ions with the electrodes, which have sufficiently large negative voltages in the afterglow. The model calculates the time-dependencies for electron densities in plasma afterglow based on experimental decay times for metastable density and electrode bias. The effect of secondary emission on electron density in the afterglow is estimated by varying secondary emission yields. It is found that this effect is less important than metastable pooling. The case of dust-free plasma afterglow is considered also, and it is found that in the afterglow the effect of secondary emission may be more important than metastable pooling. The secondary emission may increase thermal electron density ne in dust-free and dusty plasma afterglows on a few ten percentages. The calculated time dependencies for ne in dust-free and dusty plasma afterglows describe well the experimental results.

Temporal dusty plasma afterglow: A review

“…In addition, the thermal electron density increase due to secondary electron emission is about a few percent in both dusty and dust-free plasma afterglows. However, while the simulation results of Denysenko et al [70] are in good qualitative agreement with experimental measurements, there is a quantitative discrepancy, especially in the late afterglow. It was suggested that this discrepancy might be due to a deviation of the EEDF from a Maxwellian distribution.…”

“…They showed that the negative self-bias voltage that remains on the powered electrode during the afterglow (the self-bias voltage decays exponentially as in an RC circuit) is sufficiently large to induce secondary electrons by collisions between the positive ions and the electrode. Using a time-dependant zerodimensional, space-averaged global model taking into account thermal electrons with Maxwellian EEDF, energetic electrons generated by metastable-metastable collisions (metastable pooling), and secondary electrons generated by ion collisions with the bias electrodes, Denysenko et al [70] were able to estimate the effect of the secondary electron emission on the afterglow electron density as a function of the secondary emission yield. They reported that the effect of secondary electrons is not as large as metastable pooling in the dusty plasma afterglow, while in the dust-free afterglow, their effect might surpass metastable pooling.…”

“…where ε 0 is the vacuum permittivity. To obtain a good picture of the evolution of a plasma afterglow, it is generally sufficient to consider specially averaged global model [Lieberman and Ashida [105] and Liu et al [40] for dust-free discharges and Denysenko et al [65,[70][71][72][73]99] and Couëdel et al [61,82] for dusty plasma].…”

“…The different time scales in the afterglow are summarized in Table 1. As can be seen, the electron cooling time τ T is always of the order of a few tens of μs and, thus, in some studies, the electron cooling stage is sometimes simplified to a simple decay of the T e with a time constant τ T set to a few tens of μs [70].…”

Argon/dust and pure argon pulsed plasmas explored using a spatially-averaged model

“…Firstly, the increase of the electron density in the early afterglow was attributed to the release of electrons from the dust particles by secondary electron emission in ion-dust collisions [25]. The other sources of electrons in the early afterglow were identified and compared, such as electron generation in metastablemetastable and metastable-dust collisions [22] or secondary electron emission from electrodes [26]. In a presence of impurities, such as acetylene, the metastable -acetylene collisions make a significant contribution to the described phenomenon [27].…”