PPPS-2013: Investigation of plasma microwave interaction during the start up of a plasma torch, by determine the time dependent complex reflection

Summary form only given. A method of investigating the interaction between plasma and microwave @ 2.45 GHz is presented, which is based on two new approaches. On the one hand a plasma torch was developed with a cavity free excess to the forwarded and reflected wave, which in this case only depends on the interaction between microwave field and plasma. Due to the ability of self igniting it was possible to investigate the time dependent start up behavior of the plasma. On the other hand forwarded and reflected wave were characterized by a vector based detection system with a time resolution of 0.5 μs, which can provide the time dependent complex reflection coefficient. This system was used besides the standard method based on detection diodes, which only can provide absolute values of forwarded and reflected wave with a restricted bandwidth. By optimizing the detection method it was possible to handle the ripple caused by the used fast microwave source, consisting of a 2 kW magnetron and a house made switching mode power supply. With these new approaches the time dependent complex reflection coefficient during the start up of the plasma source was measured in a pressure range from 5 mbar to 80 mbar, for the gases Ar and N₂ and absorbed powers between 25 W and 400 W.