A tandem radio‐frequency plasma torch

The flow and temperature fields in a tandem radio‐frequency (rf) plasma torch were calculated. The method employed here is based on our previous rf plasma model. The flow and temperature fields of this tandem plasma show similar features to those of a dc‐rf hybrid plasma, and the carrier gas can be injected into the high‐temperature region (∼9000 °C) of the second plasma by regulating the linear velocity of the sheath gas. As might be expected, the derived results suggest that the tandem plasma has a possibility to give higher efficiencies for practical processing than conventional rf plasmas. A new type of tandem rf plasma torch was designed based on the results of the calculations. The stability of this plasma was examined under various conditions. Thus, a stable plasma could be maintained even when carrier gas of high flow rate (∼5 ℓ/min of H₂) was injected into the top of the second plasma. These theoretical and experimental investigations showed that the tandem plasma torch is an effective reactor for the preparation of refractory compounds by plasma chemical vapor deposition processes.