US1967537A - Electron tube for high voltages - Google Patents

Description

July 24, 1934. C. REINSCHLD 1,967,537

ELECTRON TUBE FOR HIGH VOLTAGES I I Filed Feb. 13. 1930 @uf MMM/f 57h den/or ye @MMM Hf/Orne y Patented July 24, 1934 1;UNITED-.Sme

ELECTRON -TUBE FOR HYIGH-V-OLTAGES f I f v l i K Carlvlteinschild, .Rahlstedt Vnear Hamburg, Gerf many, assignor to C. H. F. Muller Aktiengeselli schaft,` Hamburg, Germany', aA corporation of Germany Y f 1 f f Application February y1s, i930, serial No, 428,139 Y In Germany December 24, 1929 l My invention -relates'to' improvements in electronvtubes for high voltages.

In'order toreduc'e the voltage drop between the cathode and anode'in electron tubes for high -5voltages, particularly in valve tubes for X-ray systems, and-to prevent deformation of the filament of the glowing cathode by the action of the strong electric field of the anode and the breakdown ensuing therefrom, it has been proposed to dispose the cathode in the axis of the tube freely relatively to the anode, that is without providing means for protecting the anode in the field, such as screens or collecting devices, and the filament of the cathode has been made in the form of an jarc the apex of which is located close to the anode, the said filament being supported at both ends.

In order to provide a filament of the length necessary for high electron emission, a plurality of arc-shaped filaments have been disposed one beside the other, or in a cylindrical anode a glowing wire has been provided which was supported at suitable points.

In this construction it was not necessary to provide a glowing filament which is particularly stiff. But the number of the points located close to the anode in such a construction is comparatively small, particularly if the anode is made with a plane bottom, as is usual in View of the manu- 3@ Vfacture thereof. Therefore the voltage drop is always high.

The object of the present improvements is to reduce the voltage drop in tubes having long filaments, and with this object in view my invention consists in providing a tube in which the glowing cathode, which preferably is in the form of a glowing wire, and which is made stiff by being curved, is located in a plane parallel to the opposed surface of the anode, which surface is located perpendicularly to the axis of the tube. In this construction the filament of the glowing cathode is comparatively long, and many points of the lament are located close to the anode. Therefore the tube has a high emission and a lsmall voltage drop between anode and cathode. By providing a filament which is made stiff by being curved supporting means are necessary only at few points. Thus the tube is comparatively simple in construction, and yet there is no danger o of break-down by deformation of the glowing filament by the action of the field of the anode.

For the purpose of explaining the invention two examples embodying the same have been shown in the accompanying drawing in which the same {a-reference characters have been used in all the views to indicate corresponding parts. In said drawing,

Fig. 1 is a sectional elevation showing the tube,

Fig. 2 is a detail perspective'view showing a part'of the anode and the cathode of Fig. 1 to an 'B enlarged scale, andI Fig. 3 is a sectional elevation showing a modification.' i

In the construction shown in Figures 1 and 2 the X-ray tube comprises an envelope a of glass, a tubular anode b having a plane bottom k disposed perpendicularly to the axis of the tube, and a glowing cathode c. The cathode consists of a helically wound wire of tungsten or other suitable metal, bent into the form of a ring or annulus, the said ring being connected at both ends to the leading-in wires d and e of the heating current. The ring is supported by the said leading-in wires f and g and by three additional rods h connected to the wire at suitable points and fixed to a block i of glass supported on the tube in a manner known in the art.

The plane including the ring c is perpendicular to the axis of the tube and therefore parallel to the bottom or opposed surface k of the anode b. The individual coils of the helically wound wire are comparatively small, so that the wire c is comparatively stiff.

The distance between the bottom k of the anode b and the glowing cathode c depends on the potential difference for which the tube is designed, and many points of the wire c are located close to the bottom b of the anode, because the wire is bent into a ring having its plane parallel to the bottom of the anode. Therefore the voltage drop between anode and cathode is small. By providing a helically wound wire the cathode is long, so that the electron emission is high. For example, if the electron tube is used as a valve tube in an X-ray g5 system and with a potential of 100,000 volts, the voltage drop is on an average reduced by 15% as compared to a glowing wire consisting of an arc-shaped wire having its apex at the side of the bottom lc of the anode b. By reason of the stiffness of the helical wire c three additional supports h are sufficient for preventing deformation of the glowing wire between the leading-in wires f and g. Thus the cathode can be manufactured at low cost.

In the modification shown in Fig. 3 the construction of the cathode c is the same as that described with reference to Figs. 1 and 2, but the anode is in the form of a hollow body or inverted cup having a closed end m and a cylin- 110 drical side wall n. The anode is made from tungsten or molybdenum, and its Wall is so thick that it does not allow the passage of X-rays therethrough. Within the said cup the helically Wound glowing wire is located which is bent into the form of a ring, and which has its plane parallel to the closed end m of the anode.

The said valve tube is contructed in the form of a metal tube, the envelope consisting of upper and lower portions a of glass and a median portion o made from chrome-iron alloyv increasing the safety against break-down of the tube. Between the cathode c and the end of the tube, but Within the cup-shaped anode m, Y'n the support of the cathode carries an insulated plate p of tungsten preventing the passage of light and X-rays from the anode.

In this construction of the anode the helically wound wire c is not only parallel to the opposed surface m of the anode, but it is also surrounded at itsside by the anode cylinder n. Thus the number of the points of the wire located close to the anode is further increased, and the loss of voltage is reduced accordingly. Practically all the electrons must be transmitted from the glowing wire c to the anode m, n.

If desired the chrome iron cylinder o may be reinforced by lead or other means adapted to absorb X-rays. The length of the valve tube shown in Fig. 3 is reduced in view of the principle of the distribution of the voltage as compared to a valve tube comprising a glass envelope. Ordinarily Rntgen apparatus require much space, and they cannot easily be operated by reason of the extended insulation needed in the apparatus. Therefore the reduction of the length caused in my improved system Vis important.

In the valve tubes described above the glowing filament c may also be bent into zigzag form, consisting of a plurality of loops or rings which are located Within a plane parallel to the bottom of the anode. l

I claim:

A high-voltage electron-discharge tube comprising an envelope, a coiled concentrated lamentary cathode in said envelope adapted to emit electrons, an anode in said envelope having a substantially fiat surface lying in a plane perpendicular to the axis of the tube, said cathode being in the form of a loop lying in a plane closely spaced from and parallel with said surface of the anode, and means supporting the cathode intermediate the ends thereof.

CARL REINSCHILD,

Images