US2115927A - High voltage electron discharge device - Google Patents

Description

ay 3,1938. 5. HIRSCH 2,115 9 7 HIGH VOLTAGE ELECTRON DISCHARGE DEVICE Filed Feb. 21, 1934 2 Sheets-Sheet 1 10* 15 4 2p V 9 1'5 W I 19 11 I 1 I A2.

I 1 1 I I 1 I I I I I r I I 1 1 I I I I I I I I I I I I I I 1 n I I I I 1 I I r 1 1 I I! SAMUEL HI RSCH IN VEN TOR.

BY w

TORNEYS.

y 1938. s. HIRSCH HIGH VOLTAGE ELECTRON DISCHARGE DEVICE Filed Feb. 21, 1934 2 Sheets-Sheet 2 Samuel Hirsch INVENTOR.

Patented May 3, 1938 i UNITED STATES PATENT OFFICE HIGH VOLTAGE ELEoTRoN DISCHARGE DEVICE Samuel Hirsch, New York, Y.

Application February 21, 1934, Serial No. 712,441

Claims. (01. 250--35) This is a continuation in part of my pending mains essentially of the same length as the application Serial No. 651,316 filed January 12, straight line path that the applied voltage would 1933. otherwise jump.

V More definitely stated, my invention consists The form or shape of discharge tubes of the 5 in a novel design of evacuated discharge tubes prior art is lengthwise or tubular with the used for the purpose of producing various kinds direction of the greatest field intensity and of of electronic discharges such as X-rays, cathode the discharge along the greatest dimension of or Lenard rays or the various ionic discharges the tube; the form or shape of discharge tubes through which charged nuclei, neutrons, deutons, of my invention is flat, pancakeor in crossetc., are produced. My new design ofiers special section dumbbell-like with the direction of the 10 advantages in all those cases when either it is discharge or of the. greatest field intensity along desirable that the discharge tube should be exthe smaller dimension. The bulb or the laterally ceptionally small or short in length or when it extending portion of the tube therefore serves is necessary to produce extremely high accelerathen as a voltage barrier or as a means for intion of electrons or ions through the application creasing the creepage and sparking path length 1 of correspondingly high voltages to the electrodes between the voltage carrying points in air, beof the discharge tube. tween which in the absence of the barrier or Tubes of this kind, as constructed according to bulb of the tube, there would be sparking over the designs of the prior art, were developed with by the applied voltages. 6 their greatest dimension lengthwise in the direc- 'Yet there are fur her advanta s embod d in tion of the discharge. Thus the length of an the construction of my invention. Thus the cool X-ray tube, a cathode ray tube, a valve tube or ing of the electrodes, especially of the anode, was other similar tube was governed by the voltage hitherto effected through th application of a to be applied to it. The crosswise or lateral dicooling uid w ich is ca s d to be c rculat d mension then being always considerably less through or arou the a e p Which t than the lengthwise dimension resulted in that discharge is directed, or through the conduction almost entirely the insulating strength of the of heat along the stem of the target. But in the air in a straight line was depended upon to pretube of the longit design of the Prior vent sparking over; the path over which a disthe anode stem is necessarily quite long and charge can thus take place is then nearly 9. hence the cooling function is definitely limited. go straight line path and the bulb of the laterally With the design of my invention it is possible to extending portion of the tube did not enter apmake the anode stem much shorter to the extent preciably as a factor for increasing the length that the target upon which the heat is generated of the discharge path over that in a practically and the heat absorbing mechanism, radiator, etc., straight line from one electrode to the other. In may be brought very much closer together and this sense, therefore, the length of the insulative hence the distance of travel for the heat is or glass part of the discharge tube was governed markedly reduced and the efficiency and rapidity by the voltage which it had to stand without of the cooling is thereby increased in proportion. sparking over taking place through the air. A further advantage of my invention resides 40 In a tube of my invention the free ends of the in the fact that instead of a glass connecting tube '40 electrodes may be brought closer together than between the pump and the tube which issealed the straight linear sparking distance between the into the body of the tube for the purpose of evacelectrodes in air. This is due to the fact that uation, it is feasible to make a metallic tubular the lateral dimension of the bulb is increased to vacuum tight connection usually between the such an extent, that the discharge from the noncathode and the pump. Thus a copper or other 45 insulated portions of the electrodes either suitable metal tube is soldered or Welded into through air or through a cooling and insulating the metal of the cathode or the anode. From medium is not in a straight line but around the there on it leads to the pump. Thus there are laterally extending portions, such as the enlarged avoided the difiiculties of sealing a glass connecbulb, fins or the body, of the tube. This expedition between the tube and the pump and also 50 ent, therefore, allows the bringing closer togeththere is avoided any'danger of strain on the glass er of the exposed or non-insulated terminals of connection tube as used in the prior art which the tube, at the rate at which the diameter of under the circumstances can usually not be very the bulb of the tube is increased or so long as well annealed. A metallic tube is elastic and flexthe path of a possible discharge through air reible and the sealing-off process, after evacuation, 55

is simply carried out by pinching the tube flat and then fusing the flattened portion with a hot flame. When thus sealed off, the protruding end can then be bent out of the way and if desired an electrical connection can be made to and through it to the electrode.

With regard to the form or shape of the discharge vessel I have discovered that from increasing the lateral dimension, i. e. that at right angle to the direction of the greatest field intensity over that in the direction of the field, there results an increased peripheral space which performs a very advantageous function during the time of the discharge. At the moment when an electrical field is produced between the discharge electrodes there exists between these electrodes a smaller gas pressure than in other parts of the discharge vessel. lihis is so in particular when the degree of evacuation is not quite as high as it normally should be. Then the gas particles present in the discharge vessel are repelled from the discharge space and they crowd together either in the electrode stems or in the peripheral space at right angle to the greatest field intensity. Therefore, this enlarged peripheral space resulting from the larger diameter of the glass vessel in a plane at right angle to the greatest field intensity will increase the chance of thus crowding more gas particles into a space where they do not interfere with the normal pure electronic discharge. The form and shape of the discharge vessel conforming to my invention, therefore, either allows the operation of a discharge tube at a higher voltage and load or the presence of a larger amount of gas without causing any disturbances as in comparison with tubes of the prior art.

The discharge tubes of the prior art are usually made with glass walls of a thickness sufficient to withstand the external pressure and the thickness of the wall is then not utilized to any marked glass.

extent for supporting the tube. Thus the discharge tubes are then supported by the ends in insulating clamps or mountings which do not set up any electrical or mechanical strain on the In tubes of my invention the glass walls are normally made considerably thicker whereby, I found, the danger of puncturing and of accidental breaking are considerably lessened. In many instances I found it advantageous to support my tubes not as is usual at the ends but to place the supporting member around the largest portion of the bulb in the zone of greatest extension.

In Fig. 1 is shown, in cross section, an X-ray tube 1 supported in the reentrant portion of a housing containing a high tension transformer, a filament heating transformer and conductors to the terminals of the tube.

Fig. 2 shows more specifically a square or rectangular form of an X-ray tube of the type housed in the said transformer housing shown in Fig. l. The anode 3| is provided with a tubular cooling extension which affords good cooling to the seal-in joint with the glass while one of the conventional cooling mechanisms can be placed into the extension.

In Fig. 3 is shown, in cross section, a bilaterally reentrant glass vessel 46, sealed to it the anode 4] through the feathered edge 41 and the cooling and heat absorbing body 45 is shown screwed into the body of the said anode. The cathode 44 is shown with a straight coil filament, a metal tube 43 soldered into the body of the said cathode but open into the space to be evacuated and an insulated conductor 42 to the said filament. This filament is therefore heated by the current applied to the insulated conductor 42 and the tubing 43. The shape of the cathode shown is flat and it is sealed on to the glass vessel through a feathered flange 48 being part of the body of the cathode.

The X-ray generating potential is applied to the cathode such as to tube 43 and the anode part 45. The sparking path is then around the glass vessel 48 and the maximum voltage that can be applied to this tube is approximately that which can be applied toan ordinary tube equal in length to the distance from the metal part 45 around the bulb 46 to the cathode parts. The body of the tube therefore serves as a barrier for a voltage the sparking distance of which is greater than the straight line distance between the anode part 45 and the cathode. Also the path for creepage is around the body of the vessel and hence much longer than in the straight line type of tube. The effectiveness of this barrier depends on the insulative strength of the glass of the vessel and the evacuated space within it.

A valve tube is shown, also in cross section, in Fig. 4 consisting of a filamentary cathode 52 and a cylindrical anode 51 surrounding it; these are supported on stems 54 and 59 respectively which may be insulated and which are sealed into the glass vessel 55 in the aforedescribed manner. The glass vessel 55 is provided with extension rings or fins which are for the purpose of still further increasing the electrical barrier function of my invention. These fins may be solid as shown in Fig. 4, or they may be hollow and part of the evacuated space within the vessel as is shown in Fig. 5. Here 63 is an X-ray cathode and 64 is an X-ray anode in the sense illustrated in Fig. 3.

Still another method of carrying out my invention is shown, also in cross section in Fig. 6. Here 16 is an X-ray cathode, 15 an X-ray anode, T2 is the body of a glass vessel into which the electrodes are sealed as described. H and 18 are two electrical barrier discs made of glass or other high dielectric material. These discs are in contact with the glass vessel 12 and are either united with the glass vessel by fusion or through a cement of good dielectric strength so that an electrical discharge from the anode 15 to the cathode 16 can not take place except from the anode 75 around the barrier disc 18, the body of the vessel I2 and the disc H to the cathode 16, or in the reversed direction.

This method of construction is therefore suitable to construct discharge tubes of more or less spherical shape and with short terminals. Then the principle of my invention is applied by placing the two discs 18 and II over the terminal ends of the tube and uniting them with the body of it with a good non conducting cement and thus the possibility of applying higher voltages according to my invention are realized.

Having thus described several ways in which the principle of my invention can be carried out, I do not confine myself only to the exact details shown thereof but to the scope of the claims.

I claim:

1. A pan-cake-type highly evacuated X-ray tube to be operated at high voltage comprising an envelope of dielectric substance having substantially parallel fiat end walls and a cylindrical middle portion of a diameter greater than the distance between said walls, said flat walls and said cylindrical portions joining in rounded portions,

X-ray discharge electrodes mounted centrally in opposite end walls, whereby the said flat end portions constitute dielectric barriers to lines of force.

2. A pan-cal e-type highly evacuated discharge tube to be operated at high voltage comprising an envelope of dielectric substance, having substantially parallel fiat end walls and a cylindrical middle portion of a diameter greater than the dis tance between said walls, said flat walls and said cylindrical portions joining in rounded portions, electron discharging and receiving electrodes mounted centrally in opposite end walls, whereby the said flat end portions constitute dielectric barriers to lines of force,

3. An X-ray tube comprising a highly evacuated envelope of high dielectric substance having flattened substantially parallel end walls and a cylindrical middle portion joining said end walls in rounded portions, an X-ray cathode and an X-ray anode mounted centrally and oppositely in said flat end portions, the distance between said end portions being less than the diameter or" said middle portion and the active portion of one of said electrodes being located substantially in the center of said envelope, whereby the said flattened end walls and the evacuated space in said envelope constitute dielectric barriers to lines of force when said tube is energized with high voltage current.

4. An X-ray tube comprising a highly evacuated envelope of high dielectric substance having flattened substantially parallel end walls and a connecting middle portion joining said end walls as an integral part of said envelope, the flattened end walls having a diameter greater than the distance between said end walls and having an anode and a cathode oppositely and centrally mounted in said end walls, the said anode having a target face and a part for transmitting heat to a cooling medium outside said envelope and a solid mass of heat conducting metal connecting between said target and said heat transmitting part and said connecting metal being less in length than the distance between said flattened end portions of said tube, whereby the heat generated on said target is readily transmitted to a cooling medium.

5. An electron discharge type X-ray tube comprising an evacuated envelope having a tubular middle portion of material having high dielectric properties and substantially flattened, end portions joining said middle portion in a rounded continuous portion of said envelope and having in the center thereof cone-shaped inwardly pointing portions in each of which one of a pair of X-ray electrodes is mounted, the distance between opposite walls of said tubular middle portion being greater than the distance between said end portions whereby the wall of said envelope constitutes a barrier to voltages applied to said X- ray tube.

SAMUEL HIRSCH.

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