Patent GB-708325-A (GB)
Title: Improvements in and relating to electric discharge devices
IPC: H01J17/12
Filed: 1952-04-21
Abstract: 708,325. Metal vapour discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., April 21, 1952 [April 19, 1951], No. 9961/52. Class 39(1) A grid-controlled electron discharge device having a metal vapour filling of caesium, rubidium, or alkali-metal alloys thereof, has means for circulating cooling fluid past the reservoir of liquid metal; an electrode, and a grid-supporting ceramic structure, in that order. The tube shown, which is intended to operate with the liquid caesium reservoir at about 150C, maintaining a vapour pressure of about 10 microns, is similar to that of Specification 671,700, modified by the addition of a grid. The cylindrical wall 1 forms the anode, and is closed by headers 2 and 26 at its ends. The cathode support cylinder 3 passes through and is supported from the lower header 2 by a system of metal sleeves 5, 6, 7 including a cylindrical ceramic insulator 4. The cathode comprises a number of vanes extending radially from cylinder 3 and covered with mesh 9, and is enclosed by a perforated heat shield 10. The interior of cylinder 3 is independently evacuated, and houses the heater 13, for which 20 and 22 are the terminals. The header 2 has an inner stiffening ring 23, with a flange 24 serving to enclose between itself and the outer wall a reservoir 25 of liquid caesium. The grid support cylinder 28 passes through and is supported from the upper header 26 by a system of metal sleeves 29, 30, 32 including a cylindrical ceramic insulator 31. Concentrically within it is exhaust tube 38. The grid structure, preferably of iron, comprises a pair of hollow ring headers 42, 35, joined by tubes 36, so that cooling fluid may circulate therein. A cooling jacket 46 surrounds the anode 1, with a spiral baffle 47 between. The jacket is closed at its ends by headers 48, 49, joined via a series of sleeves to support cylinders 3 and 28, bellows 50 and 51 allowing for expansion. Spiral baffles 61, 63 and 62, 64 are provided for circulation of cooling fluid. This enters through inlet 60, passes up round the lower end of the device, and through an opening 67 into the outer jacket 46. At the upper end of the jacket the fluid comes out through an opening 68, flows round the upper end of the device and through an opening 45 into the annular space between cylinders 28 and 38, which is divided into two longitudinal sections by baffles. The fluid flows down one of these sections, into the grid structure; this has a system of partitions, so that the fluid flows down through one half of the structure, and up through the other half, finally leaving the device through fitting 43. Since the fluid must be non-conducting, and unaffected by the high temperatures, water is not suitable; silicone oils are suggested. As the fluid passes the caesium reservoir at an early stage, this will be maintained at a lower temperature than the anode, grid, and upper insulator 31, so that there is reduced likelihood of caesium condensing on these members and causing leakage or secondary emission. Although lower insulator 4 is reached by the cooling fluid before the caesium reservoir 25, it is maintained at an effectively higher temperature because of additional heat from cathode cylinder 3. An external heater winding 65 may be provided for initially bringing the device to operating temperature.