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A power frequency plasma torch is described specifically designed for application to industrial heating processes using a magnetically rotated radial arc for which efficiency and reliability were considered to be the main criteria. Operation at moderate supply voltage with a high overall circuit power factor is obtained by using a separate ignition supply for reigniting the arc at each half-cycle. The design is based on a wide range of preliminary investigations many of which may be applied to both ac and dc plasma torches or other arc operated devices. The operating characteristics of the plasma torch are given, and a thermal balance has been carried out enabling the efficiency to be accurately measured. An efficiency greater than 60 percent has been measured in this way.