Abstract: An electric arc reactor having a substantially straight feed material passage extending through both the anode and the cathode. Gas is fed into the gap between the two electrodes so as to swirl about the axis of the feed passage and thereby confine the lateral extend of the arc and also confine the location at which the upstream arc root attaches to the upstream electrode. An enlargement of the passage in the gap end of the upstream electrode provides an internal sloping root attachment surface. A similar enlargement may be provided in the downstream electrode, but spaced from the gap, if the downstream electrode forms the cathode. Gas flow in a direction towards the upstream end of the feed passage is used to control the location at which an arc root attaches to the sloping surface of a passage enlargement. Magnetic means is provided to induce rotation of the arc such as to form a hollow arc column which is coaxial with the feed passage and through which feed material can pass.

Abstract: A circuit for pulsing the output of a dc power supply (2) connected across a load such as a welding arc. The circuit has a first SCR (12) connected in parallel with a resistor (14). The SCR (12) controls the pulse current and the resistor (14) controls the background current. Each pulse is terminated by the action of a second SCR (18) and a capacitor (16) connected across the first SCR (12) by applying a control pulse to the gate of a second SCR (18). The capacitor (16) is charged by a power supply (20) and is connected by the second SCR (18) so that the first SCR (12) is reverse biased and hence is turned off to terminate the pulse. Immediately the first SCR (12) turns off, the capacitor (16) is charged in the opposite sense to the charge derived from the power supply (20) and this in turn causes the second SCR (18) to be reversed biased by conduction through the resistor ( 14) and turned off a short time after the first SCR (12) is turned off.