Improvements in or relating to apparatus for producing a high velocity gaseous stream

920,079. Arc plasma generators. BRISTOL SIDDELEY ENGINES Ltd. Sept. 29, 1961 [Oct. 14, 1960], No. 35218/60. Class 39 (3). [Also in Group XXXIII] A pair of concentric electrodes together form an annular convergent-divergent nozzle through the throat of which a working fluid axially flows, and across which a radial arc can be maintained, the arc heated working fluid being discharged from the nozzle into a chamber, which chamber is itself provided with an outlet nozzle for the discharge of the high velocity hot gas, which may be supplied to a hypersonic wind tunnel. Hollow cathode 4 and anode 3 define an arc chamber 1, into which a liquid oxygen/nitrogen mixture is introduced tangentially via spaced peripheral holes 6, to be evaporated by the arc maintained across the throat 12, the resultant gas being ejected into chamber 8 and thence from nozzle 9. The liquid is pumped, to act as coolant, via inlet pipe 13 and the hollow wall of nozzle 9 and chamber 8, through the helical passage formed by the partition 10 in the hollow wall of the anode 5 to the gallery 7, and thence to holes 6 and, via pipe 14, down the interior of the cathode 4; the pump 14 may have a bleed to the pump inlet for the control of the liquid supply. Further cooling of the cathode 4 and the throat of nozzle 9 is provided by the continuous evaporation of films of the liquid produced on their surface by the fine holes 15 and 17 respectively. Alternatively, by the use for these parts of the apparatus of porous walls, or of inserts formed of porous material or of fine metal tubes, sweat cooling may be employed; or those ports may be interchangeable with similar ports to permit either film or sweat cooling. A coil 20 may be connected in series with the electrodes; and several arc chambers may feed a single chamber 8, permitting a greater gas blow, and control of the gas temperature by the supply of cold air from one of the chambers the arc of which has been extinguished. In a modified method of use, compressed air may be fed directly to the arc chamber to constitute the source of gas. A modified cathode construction (Fig. 2, not shown) permits the use of a liquid metal, instead of the working fluid, as coolant, and enhances the Peltier cooling of the cathode. Specification 897,577 is referred to.