US 1211091 A
Description (OCR text may contain errors)
W. D. COOLIDGE.
CATHODE RAY DEVICE.
APPLICATION FILED SEPT. 8. 1913. RENEWED SEPT.26' 1916.
1 21 ,09 1 o a) Patented 'Jan. 2, 1917 v Inventor: William D.Coolidc$e,
Hisfltto WILLIAM J). COOLIDGE, OF SGHENECTADY, NEW YORK, ASSIG -NOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION .OF NEW YORK. I
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Application filed. September 8, 1913, Serial No. 788,566. Renewed September 26, 1918. Serial Flo. 123,815.
To all whom it may concern Be it known that 1, WILLIAM D. GooLmon, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements" in Cathode-Ray Devices, of which the following is a specification.
The present invention relatesto the construction of X-ray or vacuum discharge tubes operating with a pure electron discharge independent of gas ionization, and it comprises certain novel structural details in tubes of the type such as described in my prior application, Serial No. 766,549, filed May 9, 1913.
in accordance with one feature .of my present invention the current-carrying capacity of the tube with a given cathode temperature and voltage has been materially increased by arranging the heated, electronemitting part of the cathode in one plane, for example, by coiling it in the form of a fiat spiral.
My invention will be best understood by reference to the following description taken in connection with the accompanying drawings, in which- 7 Figure 1 is an outline drawing of the tube as a whole showing the relation of the various parts, and Fig. 2 is an enlarged view of the electrodes. V
The inclosing envelop 1 of the X-ray tube consists of a materialpervious to X-rays, for example, of a lime glass known on the mar ket as German glass, and is provided with an anode 2 and a cathode 3. The cathode may be said to consist of two parts, a heated portion 25, and an unheated part21, as will be hereinafter more fully described. The heated part of the cathode consists preferably of ductile tungsten although other highly refractory material, for example, tantalum may likewise be used. The tube 21 may consist of either molybdenum or tungsten. The stem 4 of the anode is attached by means of a tungsten or molybdenum wire 5-to a rod fi'which may consist of molybdenum and which passes through a molybdenum, which serve to both supfport tubular extension 7 of the tube. The end of the rod 6 is attached by means of a wire 8, consisting convenientlyfof molybdenum, to a platinum leading-in wire 9. The tubular extension 7 of the anode end of the bulb and a similar tubular extension 10 of the cathode end serve to increase the distance between the terminals. The rod 6 is welded or riveted to a number of split cylindrical tubes 11 of refractory metal, preferably the anode rod and conduct heat away om it to the glass so as to protect the seal. These cylindrical supports, most conveniently are made of resilient metal so as to grip: the inner surface of the glass even'though it is somewhat uneven.
The cathode end of the tube is provided with an inwardly projecting stem 12, the tip of which consists of somesuitable heatresisting insulating material,l for example,
.efiicient. Such intermediate glasses may be made by mixing the two materials to be joined. The conductors 14, 15, which supply heating current to the cathode are err.- bedded in the stem 12 and are attached respectively by copper wires 16, 17, to platinum leading-in conductors 18 and 19, joined thereto by welding. A glass tube 20 surrounding the wire 19 serves to insulate the wires 18 and 19 from each other. The cathode may be heated by attaching the conductors 18, 19, to a suitable insulated source of energy, such as a storage battery, (not shown in the drawing).
The tube 21 surrounding the heated part of the cathode is attached toand supported Patented Jan. 2,1Q13.
23, also embedded in the tip of by wires 22 lhe tube 21 serves to focus the the stem.
cathode rays upon the anode and for this purpose is preferably brought to the same potential'as the cathodeby' electrically connecting it to the cathode by means of a small tungsten or molybdenum wire 24. It also prevents a discharge of electricity fromthe heated part of the cathode in a directlon away from the anode.
As fully set forth in my copending application, a tube of the general character above described operates independently of gas gas, by both subjecting them to a high temperature and also to the. gas-freeing influence .of the cathode discharge itself during exhaust. As already mentioned the cathode discharge is focused upon the target by theconductive ring or cylinder 21, which so modifies the static field in the tube as to direct the electrons upon a spot of limited area. I have found that when the cathode is given a linear extension in a direction parallel with the axis of the focusing member that only the tip of the cathode is effective to furnish electrons to carry the current. When the filament, for example, is given the shape of a helix or loop, the static field of the filament near its tip appears to repel the electrons from the other parts of the filament back of the tip which are further removed from the anode than the tip. Hence the electrons carrying-the current are furnished largely by the tip. This has the effect of greatly limiting the amount of current which can be transmitted through the tube with a given filament temperature and at a given voltage.
I have found that by disposing the oathode in a plane substantially normal to the axis passing through the focusing device and the anode, the discharge current may be very materially increased. Such a shape may be conveniently given to the cathode'by coiling the cathode conductor 25 in the form of a fiat spiral although it is obvious that other shapes, for example, a zig-zag grid may be used with the same effect.
In the X-ray tube above described all exposed metal parts consist of either tungsten or molybdenum which I have found may be very completely freed from gas.
Another feature of novelty of the present I form of X-ray tube is the-location of the cathode 3', substantially near the center of the bulb, outof direct proximity to the Walls. I- have found this location of the cathode to be advantageous due to the fact that when the cathode projects beyond the neck of the bulb, the discharge is less influenced by static charges on. the glass, which act to reduce the current. The diameter of the spiral as indicated in the drawing is less than the diameter of the working face of the anode. b What I claim as new and desire to secure 1. An electrical discharge tube comprising an envelop, an anode, a cathode adapted to be independently heated disposed substantially in a plane normal to a line passing throu h anode and cathode, and means for focusing the cathode discharge, said envelop and electrodes being freed from ionizable gas to such extent as to render said tube operable with an electron 'discharge independent of gas ionization.
Letters Patent of the United States,
2. A cathode ray tube operable with an electron discharge independent of. gas ionization, provided with a cathode having a .heated portion disposed substantiallyin one plane perpendicular to the axis of the tube and a static focusing ring surrounding said cathode. I
3. In a Roentgen ray tube, operable with an electron discharge independent of gas ionization, an anode, an electron-emitting cathode arranged in the shape of a flat spiral located perpendicular to the axis of the tube and having a diameter smaller than the working face of the anode.
4. In an electron-discharge tube operable with a discharge independent of ionization, an anode, a cathode conductor consisting of a wire disposed substantially in a plane perpendicular to an axis passing through the electrodes, means for heating .said wire, and means for focusing the cathode rays upon said anode.
5. In an X-ray tube operable with an electron discharge independent of gas ionization, an evacuated envelop pervious to X-rays, a stem havinga tip of heat-resisting, insulating material projecting into said envelop, refractory supports joined to said tip, an anode and an electron-emitting cathode comp-rim'ng a heated conductor and j a surrounding ring of refractory conducting material carried by said supports.
6. An X-ray tube comprising an envelop evacuated to such low pressure that positive ionization is substantially absent, an anode, an electron-emitting cathode projecting out of immediate proximity to the walls of said envelop, and means for focusing the cathode discharge. p
7. An X-ray device comprising an evac- 5 uated envelop, an anode, a cathode comprising a closely Wound spiral of wirefsaid spiral having a diameter smaller than the Working face of said anode and located in a plane substantially perpendicular to a line passing through the anode and cathode 169 and means for conducting a heating current to said cathode.
In Witness whereof, I have hereunto set my hand this 5thday of September 1913.
LLIAM D. COOLIDGE: Witnesses:
BENJAMIN B. HULL, HELEN ORFORD.