Patent GB-455967-A (GB)
Title: Improvements in or relating to electric discharge devices
IPC: H01J17/00
Filed: 1935-04-29
Abstract: 455,967. Discharge devices. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London, and GABOR, D., 30, Falk Miksa Ucca, Budapest. April 29, 1935, No. 12771. [Class 39 (i)] An electric discharge device comprises a vessel containing rarefied gases and enclosing an outer discharge space containing one or more anodes, and one or more inner discharge spaces which communicate with the outer discharge space only through openings of " plasma-filters," i.e. perforated bodies with fine openings which consist of insulating material or of a conducting frame coated at least on its outside and part of the walls of the openings with insulating material, each inner discharge space containing an indirectly-heated cathode spaced a distance of the order of several, preferably 3-15, mean free paths of molecules from the filter ; a " dark discharge" is produced in each inner space, in which the current is transported from the cathode to the openings of the filter at a voltage drop too low for ionization, the ions necessary for neutralizing the electron space charge in the inner space being supplied from the discharge in the outer space through the openings in the filter. Preferably the area of the cathodes is sufficiently large, and the cathodes are heated to such a temperature, as to enable the whole of the discharge current to be supplied by zero-field emission, in which case the characteristic of the discharge becomes independent of the cathode heating. In the form shown in Fig. 2, an indirectlyheated cathode 1 is enclosed by a cylindrical filter 2 of wire gauze coated partly with insulating material. End plates 7, 8 close off the inner discharge space, one plate being of transparent material such as mica to facilitate observation of the dark discharge which is set up in the inner space. A luminous glow occurs between the anode 3 and the filter, which is covered with a " cathode sheath." Dimensions of this form are given. In another form the cathode comprises two thin discs 12, 13, Fig. 5, joined together at the rims and enclosing a spiral heater 15. The cathode is supported within an insulating casing 20 closed by a filter 21 of moulded ceramic material or wire gauze. The sleeve 22 constitutes the anode. Two such beam sources may be mounted in a tubular envelope for use as a lamp working on A.C. supply. The light is produced both in the positive column and by transformation of the kinetic energy of the electron beams from the sources. The lamp may be designed so that the positive characteristic of the sources overcompensates the negative characteristic of the positive column, no stabilizing impedances being needed. The characteristics of the sources may be controlled by the provision within the dark discharge space of " ion-collectors" which intercept a large proportion of the ions on their way from filter to cathode. As the ratio of ionic to electronic current at the cathode must be constant, this results in an increased number of ions being dragged through the filter openings with a resultant increased voltage drop for the same current. Higher characterics are thus obtained. The ion-collectors may be of insulating material left floating, or of conductors maintained at cathode potential or less. In Fig. 5, the collector 32 is an insulating disc having a central aperture. Curves are given showing the dependance of the characteristic on the diameter d, other dimensions being given. In a modification, Fig. 7, the cathode 33 is of annular form and is completely screened from the filter by the apertured disc collector 36, of metal, or insulated. Diminishing the distance D in Fig. 7, has a similar effect to increasing the diameter d, Fig. 5. In other forms described the collector is a metallic grid . placed between the cathode and filter, in forms similar to those shown in Figs. 2 and 5. In these cases a variable bias may be applied to the collector for control purposes. The device may then act as a power amplifier with greatly improved amplification factor or as a lamp with variable light emission. Curves are given showing the characteristics for different values of collector bias, transconductances of 1-10 amps. per volt being attainable. By biassing the collector on a resistance in the cathode lead a more positive stable characteristic can be obtained. A formula is given for determining the diameter and depth of the filter holes so as to ensure stable working and to avoid sudden transition to an arc discharge such as is liable to occur with wide filter openings. By suitable dimensioning the characteristics can be rendered independent of the pressure and nature of the gas filling over certain ranges, which in an example are 0À3- 0À5 mms. in neon and 0À1-0À17 mms. in argon. Fillings of up to 1 mm. of neon, up to 0À2 mms. of argon, and sodium are also mentioned. Specifications 441,204, 442,307, and 455,009 are referred to.