Broadband microwave absorption effects in 2D nitrogen capacitively coupled plasma under different operating conditions

Abstract

In recent years, the interaction of electromagnetic waves (EM) with plasma sources under argon and helium discharges has been extensively studied due to its potential applications in plasma stealth. However, nitrogen, as a more economical discharge gas, has been ignored in terms of its absorption of EM waves and stealth effect. In this work, a numerical calculation model combining two-dimensional capacitively coupled plasma (CCP) fluid model and EM wave model was developed to investigate the plasma uniformity degree and broadband microwave absorption effects in helium and nitrogen CCP. It is concluded that the two-dimensional model in this paper has more accurate and reasonable through comparison with the one-dimensional and experimental results in helium CCP. Nitrogen CCP shows better broadband absorption effects than that of helium, and helium plasma has better uniformity than nitrogen under the same discharge parameters. But the uniformity degree of nitrogen plasma is not much different from that of helium under the same electron density, which means that nitrogen can significantly improve its broadband wave absorption properties to some extent without loss of uniformity degree. Based on the above conclusions, the absorption characteristics of nitrogen CCP under different radio frequency (RF) power and pressure are analyzed. The attenuation effect of nitrogen CCP increases with the increasing RF power, and it is interesting that the influence of pressure on the attenuation of EM waves is not monotonically increasing, and the related mechanism is discussed. Finally, discussion of skin depth under different RF power and pressure validates the above conclusions. The absorption band of nitrogen CCP under the best parameters in this work can reach the X-band, which shows great application potential in plasma stealth.