Pressure dependence of surface wave-excited plasma column sustained along metal rod antenna

A novel method was proposed to generate high-density microwave-excited plasma along metal surfaces. In our previous work, 2.45 GHz microwaves were confirmed to propagate as surface waves along the interface between overdense (>1011 cm–3) plasma and a graphite rod biased at a negative voltage against a grounded chamber. The generated plasma showed columnar structure surrounding the rod surface, and thus it was called metal-antenna surface wave-excited plasma (MASWP) column. In this work, the effect of gas pressure on the spatial distribution of MASWP column was investigated. It was confirmed that the length of MASWP column became longer along a graphite rod (25 cm in length and 1 cm in diameter) with increasing gas pressure. In particular, at an Ar gas pressure of 33 Pa, we obtained a long plasma column covering the entire surface of the rod with a negative voltage of −150 V and an input microwave power of 100 W. The same tendency, or the extension of MASWP column with increasing gas pressure was also confirmed by using a copper rod and a stainless-steel rod instead of the graphite rod. This indicates that the extension of MASWP column with increasing gas pressure occurs independently of antenna materials.