GB1274876A - Plasma arc heating apparatus - Google Patents

Abstract

1,274,876. Induction plasma apparatus; pulse generating circuits. CANADIAN TITANIUM PIGMENTS Ltd. 19 June, 1969 [2 Aug., 1968], No. 31004/69. Headings H3P and H5H. Induction plasma gas heating apparatus 10 has electrodes 38, 40, for ionizing the gas which is passed through and over the helical induction coil 11 mounted in a tubular chamber. The spacing between adjacent turns of the coil 11 is less at each end than in the middle portion of the coil, such that the plasma 55 is established in the middle of the coil. The conically tipped anode 38 has passageways 39 through which gas is injected into the space between the electrodes 38, 40, the cathode 40 being annular. A perforated metal neutralizer screen electrode 41, the electrodes 40, 41, being earthed at 42. Gas is also injected into the tubular chamber via nozzles 32, 33, between the electrodes and the coil. Unidirectional voltage pulses across electrodes 38, 40, are produced by capacitance discharge through a thyratron 65 from a series resonant circuit, 68-71, Fig. 2a, the thyratron 65 being triggered periodically by conventional means 185, 186, and the electrodes 38, 40, being transformer coupled to said discharge circuit. The correction 43 to the anode 38 is described in detail, Fig. 3, (not shown). When rectifier 73 is switched on, condensers 68, 69, charge up to a maximum at which a pulse driver unit 185 actuates a pulse control unit 186 to supply a short positive pulse to the thyratron grid 87a, condensers 68, 69, then discharge, and the process is repeated. The condenser discharge current pulses, in flowing through the primary winding P of the saturatable core transformer M, produce unidirectional voltage and current pulses in the secondary transformer winding S. This is because, as the pulse increases in P, it produces a voltage in S which rises almost instantaneously to a maximum, at which further voltage rise is cut off by saturation of the transformer core. When the current in P reaches its maximum value and then decreases to zero, no appreciable negative voltage is generated in S, since the transformer core has insufficient time to recover from its saturated state in this time interval. Hence there is impressed between the electrodes 38, 40, of the heater unit the series of unidirectional voltage pulses which produce bursts of ionized particles in the gas flow between these electrodes.