Evolution of atmospheric-pressure RF plasmas as the excitation frequency increases

Experimental results confirm the previously reported computational finding that increasing the excitation frequency of an atmospheric-pressure plasma leads to an extension of the glowlike operation mode. Furthermore, it is shown that more intense plasmas are attainable at higher frequencies due to the ability to couple more power into the plasma without inducing the transition into the γ mode. If the frequency is increased at a constant power, however, the plasmas become noticeably less intense even though more power is coupled into the electrons. This paradox is explained by the different evolution of the power coupled to electrons in the sheaths and in the bulk as frequency increases. A figure is presented.