GB1248227A - Crossed field discharge device - Google Patents

Abstract

1,248,227. Magnetrons. GENERAL ELECTRIC CO. 29 Oct., 1968 [14 Nov., 1967], No. 51292/68. Heading H1D. In a re-entrant stream crossed-field discharge tube in which axially propagating waves are generated, generally of the type disclosed in Specification 1,184,371, the cavity formed by the end spaces 55 and 57 with the interaction space 38 bounded by the inner surface 37 of the anode structure and the surface 45 of the cathode is arranged to have a resonant frequency equal to that of the folded transmission line formed by the anode members shown in Fig. 3, whereby efficiency is increased by the balancing of the R.F. voltage on the cathode with respect to that on the anode structure. In operation, axially propagating standing waves are generated which are reflected at the two ends 21, 29 of the outer annular cavity 35, pass through the radial passage 39, and are again reflected at the upper and lower open ends of the transmission line formed by the anode members of Fig. 3. The emissive coating on the cathode is provided with axially extending projections (Fig. 4, not shown) opposite the members 37 of the anode structure, and is radially stepped as shown in Fig. 2. At the upper end of the cathode, the cathode stud 43 is mounted within an insulator 62 which spaces it from a surrounding conductive tube 61 which is brazed to the pole plate 54 and hence is electrically connected to the anode structure to the outer conductive members 72 and 76, and hence to the T-shaped conductor 78. As shown in Fig. 1, the axially extending portion of the coaxial line coupled to conductor 78, and the shortcircuited arm 81, 91, are both arranged to be #/4 long at the operating frequency, while the remaining arm 87 couples the device to a load. The cathode and its heater 47 are also dimensioned to constitute a coaxial transmission line of effective length #/4, the line being closed at its upper end by an end plate 41 and the cathode stud 43, and coupled at its lower end to a further #/4 length of coaxial line formed by the heater connection 44a and a surrounding tube 94, which is insulated from the magnetic core by a plastics tube 95. This arrangement of the cathode and its heater, and of the external connections thereto, increases efficiency by minimizing losses due to circulating currents in the device. The casing 75a surrounding the device and connected to the polepieces is of magnetic material e.g. soft iron.