Demonstration and characterization of a capacitively coupled plasma torch array

Summary form only given. Streams of air blowing through an electrical discharge between a pair of electrodes, made of tungsten, form a plasma torch. In order to be able to use a single power source to supply several torches simultaneously, capacitors are used as ballasting impedances coupling all the torches together. The size of each torch depends on the geometry of the electrode pair and the streaming speed of the air flow. It has been demonstrated that an array of up to six plasma torches can be lit up simultaneously by a single AC power source (60 Hz wall plug) and the array is only limited by the power handling capability of the source. A laser beam is used to measure the dimensions of the torch. The method is to move the torch across the laser beam which is detected by a photomultiplier tube through a pin hole and a collimator. Due to the high temperature of the torch plasma (<2000/spl deg/C), the dielectric constant of the background air (whose density is depleted to maintain pressure balance) is reduced by about 3/spl times/10/sup -5/. It is large enough to diffract the laser beam and cause up to 80% intensity reduction. Therefore, it is a very sensitive diagnostic for the dimension measurement. The results show that each torch, in the shape of a cylindrical column, has a 2 cm diameter and 6.5 cm height.