Ion sheath evolution and current characteristics for a trench immersed in a titanium cathodic arc discharge

Evolution of an ion sheath and the ion current generated by a pulse voltage application are discussed for a trench-shaped target immersed in a titanium cathodic arc discharge plasma with a current of 80 A DC at a nitrogen pressure of 8 Pa. The ion sheath evolution inside the trench with a width of 30 mm and a depth of 20 mm is experimentally observed. Considering a secondary electron emission coefficient, the observed fits the theoretical result by Lieberman. From an ion sheath evolution observed experimentally, the plasma density is estimated to be about 1010 cm−3 using Liebermanʹs theory. The obtained plasma density fits well with a measured value. The ion sheath has a sharp edge at the initial stage, but the sharp edge gradually disappears due to merging of the sheath edge evolving outside the trench, which is confirmed by the current through positively biased Langmuir probe.