Abstract: A dc power supply (1) for a dc arc torch (6) comprising: an input port (4, 8) for connection to a source of direct current and an output port for connection to the electrodes (5, 7) of an arc torch; a controlled switch (2) and an inductance (3) connected in series between the input port and the output port; a free-wheeling diode (9) connected such that, in use, it is reverse biased when the switch (2) is ON, and forward biased when the switch (2) is OFF to maintain direct current flow through the arc and the inductance (3); and a feedback circuit (10) having a current sensor (11) to sense the instantaneous value of current flowing through the arc, and a control terminal (26) connected to the switch (2), the feedback circuit, in use, operating to provide a control signal at the control terminal (26) to turn the switch (2) ON when the instantaneous value reaches a first level and OFF when the instantaneous value reaches a second level.

Abstract: A gas cooled cathode for a direct current plasma torch. The cathode has a tip connected to a body. A gas passage for working gas passes through the body of the cathode, passes proximate the tip and exits the body adjacent the tip. The cathode is spaced apart from and insulated from the anode by means of a collar of insulation material.