Extension of surface-wave-excited high-density plasma column sustained along graphite rod target

In typical, surface-wave-excited plasma (SWP) is generated along dielectric antennas such as a quartz tube or an alumina disk to guide surface waves. However, recently, we introduced a new SWP sustained along the surface of a metal antenna at a negative voltage against a grounded chamber. In this work, Ar plasma was generated along a graphite rod (10 mm in diameter and 190 mm in length) at a background gas pressure of 5.7 Pa with an incident microwave power of 200 W and a negative voltage Vt   supplied to the rod. At Vt=0V, overdense SWP was sustained locally at around the one end of the graphite rod. The plasma was then confirmed to extend longer along the rod axis, with increasing Vt  . At Vt=–200V, the plasma showed a columnar structure with an electron density larger than 1011 cm−3. Note that the SWP column obtained strongly sputtered the graphite rod; thus, we considered that a new sputtering source can be developed employing this new technique, or SWPs sustained along metal targets.