GB1380719A - Apparatus for producing a plasma flow - Google Patents

Abstract

1380719 Plasma discharge devices AGENCE NATIONALE. DE VALORISATION DE LA RECHERCHE 21 Dec 1971 [23 Dec 1970] 59484/71 Addition to 1298680 Heading H5H Plasma generating apparatus comprises a plurality of convergent nozzles 34a, 34b in which no internal arc is struck supplied with plasma forming gas, and a pilot plasma generator 62 which directs a primary plasma jet 42 at the space between the nozzles to reduce the resistance between the nozzles 34a, 34b for a main arc 44 to be initiated between the conductive nozzles 34a, 34b, the pilot plasma generator 62 and the nozzles 34a, 34b, being connected in parallel across the terminals of a current source 40a, and the pilot plasma generator circuit including a resistance 66 of sufficiently high value for ensuring that the current flows preferentially through the gas flows of the nozzles once the main arc 44 between the nozzles has been established. The value of resistance 66 is preferably high enough to cause extinction of the pilot plasma blow pipe once the main arc 44 in established. The extinction of the main arc 44 may automatically restart the pilot plasma generator. The nozzles 34a, 34b may be slid away from one another once the main arc is established. A polyphase arrangement is disclosed (Fig. 2, not shown). The pilot plasma generator, Fig. 4, comprises a rod electrode 76 provided with a conductive tip 72 of copper. Cooling fluid is supplied to the hollow bore 74 in tip 72 by means of an inner tube 78. Nozzle electrode 68 has a cooling chamber 80. Electrodes 68, 76 are screwed into an insulating block 82. The electrode 76 is spaced from the walls of the block 82 so that plasma forming gas may be supplied to an ejection slot 92 between the electrodes. A grooved insulating shield 88 surrounds the electrode tip 72.