The non-luminous surroundings of atmospheric pressure plasma jets contain still substantial electron density which can be of practical importance, when e.g. reactant or precursor is introduced into this zone. Low signal-to-noise ratio makes the Stark broadening technique unsuitable there, and so we employed the microwave interferometry to determine the electron density during the plasma synthesis of graphene. The relatively long wavelength, tight geometry and the presence of overcritical plasma filament necessitated the use of a numerical solution of the Maxwell equations. Besides laying the groundwork of the method, the paper also discusses the importance of plasma density profile in the active filament and its surroundings. The results show that in radial distance ten times higher than a visually apparent plasma diameter, the plasma density was still around 10¹⁶–10¹⁷ m⁻³.

大气压等离子体射流的非发光环境仍然包含相当大的电子密度，当例如将反应物或前体引入该区域时，这可能具有实际重要性。低信噪比使Stark拓宽技术不适合在那里，因此我们采用微波干涉法来确定石墨烯的等离子体合成过程中的电子密度。相对较长的波长，紧密的几何形状以及超临界等离子体灯丝的存在，必须使用麦克斯韦方程的数值解。除了奠定该方法的基础之外，本文还讨论了活性灯丝及其周围环境中等离子体密度分布的重要性。结果表明，在径向距离上，其直径比可视的血浆直径高十倍，¹⁶ –10 ¹⁷ m ^-3。