US2434517A

US2434517A - Method of activating cathodes

Info

Publication number: US2434517A
Application number: US535052A
Authority: US
Inventors: Horst A Poehler; Lester F Keene
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1944-05-11
Filing date: 1944-05-11
Publication date: 1948-01-13
Anticipated expiration: 1965-01-13

Description

Jan. 13, 1948. H. A. POEHLER ETAL 2,434,517

' METHOD OF ACTIVATING CATHODES Filed lay 11, 1944 a r 1.9 F Mann-FM 1 1 INVENTORS I V #fl-PGEI/(EE L Ff BEA/E. B

Y MM 1 ATTORNEY Pmnas Jan. 13, 1948 METHOD OF AQTIVATING CATHODES Horst A. Poehler, Long Island City,.N. Y., and Lester F. Keene, Montclair, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 11, 1944, Serial No. 535,052

.6 Claims. (Cl. 316-4) This invention relates to a method of activat-- cathodes, thermal activation of the cathode is al-' most exclusively used. However, sometimes due to such causes as lack of reducing materials in the core of the cathode, or conversely, to presence of a large percentage of such elements as manganese, iron and the like being excessive, or, as

in the case of nickelate cathodes, to an oxidation of the reducing agent, thermal activation does not suflice. In such instances resort has been made to activation by electrolysis of the' coating as one solution of the problem, and to positive ion bombardment asanother solution. 'However, the electrolytic method is excessively time consuming, often requiring ten hours for accomplishment, and the positive-ion bombardment method which has required introduction of an inert gas, has the disadvantage of combating evil with evil and of being impractical in many instances.

Manufacture of cathodes of the character indicated is generally accomplished by first coating a base member, secondly, converting the applied coating and third, activating the converted coating. The base member may be of such material as nickel, tungsten and the like. Coating applied thereto may be the carbonate of barium, strontium and the like. For brevity in description reference will be made to the base member as nickel and to the coating as applied as one containing barium. The barium carbonate is mixed with a binder and applied to the nickel. Conversion of the coating is performed with the oathode mounted in the electronic device where it is to beused and is accomplished while the device is on the pumps for evacuation. By heating the cathode to sufilciently high temperature, the binder is driven off and the carbonate converted to an oxide, which in the instance of the selected example, is barium oxide. The gases evolved, including the volatilized binder, are carried off on the exhaust. Thereafter, the oxide is activated, usually after the device is sealed ofif. Activation is the step of manufacture to condition the cathode surface to make it capable of copious emission. The more or less accepted theory of activation is that the oxide at the surface is separated into its constituents which in the selected instance results, in a film of barium on the cathode surface and evolution of a small amount of oxygen, which of course, is a gas. In due time the oxygen combines with some metal part in the device and being so .small in amount has never been considered or found deleterious. In the present invention, the temporary presence of the oxygen is beneficial in that it promotes or supports ionization during the activating operation, but disappears before the device is put into service.

In its general aspects, the present invention has the objective of improving, simplifying and speeding cathode activation.

Another object-is to employ a novel method of ionization activation of the cathode.

Yet another object is to avoid need for specific introduction of gas for purposes of ionization.

A further object is to provide an improved method of cathode activation which is performed while the electronic device is on the pump.

Other objects will appear to those skilled in the art to which the invention appertains as the description progresses, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views:

Figure 1 is a longitudinal sectional view of an exemplary electron discharge device and associated instrumentalities for carrying out the invention; and

Figure 2 is a cross-section of said device with indication of the electron paths and magnetic field obtained by utilization of the present inven tion.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral l0 designates a cathode which is shown as of the indirectly heated type and accordingly hollow and having a heater ll therein. The specific device wherein the invention is illustrated is a magnetron having a cylindrical shell or body I2 within which and directed toward the cathode are a plurality of anode segments i3 separated by longitudinal splits or cavities I l.

Beyond the ends of the segments and within said body l2 are end spaces I5. The ends of the body I2 are sealed by plates or end caps l6. Leads i! enter through the. side of body l2, ap-

propriately connecting with the heater and one connecting with the cathode, and both functioning to position and support the cathode within the center cavity l8 within the anode. The lead supporting and sealing means I! are of appropriate construction, one being shown as having an exhaust tubulation 2|, which is sealed, as usual, after the device is exhausted.

The cathode is one known in the trade as oxide coated, and which generally comprises a nickel or other metal base having an external coating f a composition including such materials as barium, strontium and the like, utilized, at least in part, in oxide form and reduced, at least in part, by thermal or other activation. It is particularly with respect to those cathodes which fail to produce adequate emission after thermal activation that the present invention has its principal utility. The method accordingly includes, by preference, first applying thermal activation in accordance with prior art practice, and thereafter applying heating current to the heater and potential difference to the cathode and anode for obtaining electron emission from the cathode and electron fiow toward the anode.

The invention in its specific embodiment is conducted by means of positive-ion bombardment, without introducing an inert gas. In its broadest aspect, the invention contemplates, for activation purposes, increasing the distance of travel of electrons to move in paths very considerably greater than, and at least double the distance between the straight-line distance between the cathode and anode. In consequence of this increased length of path during activation, the electrons have each a greatly increased probability of collision with a gas atom, producing ions by collision. In ionization by collision an electron impacting with a gas atom imparts to it sufiicient energy to remove one of the electrons of the atom, leaving a positive ion, which in this case is attracted to the cathode and impinges upon it. The -ion has greater mass, and bombards the cathode more severely than an electron returning to the cathode. Due to action of the bombardment on the cathode, a beneficial activation of the cathode results.

For carrying out the invention, we introduce a magnetic field transverse to, or specifically at right angles to the normal electron path and electric field, so as to make the electrons follow a curved, spiral, or cycloidal path from the cathode. By proper adjustment of the magnetic field, such path of the electron can be made quite long compared to its normal path without infiuence of a magnetic field. All electrons are not precisely affected. Almost all reach the anode, although some do not, a few returning to the cathode, but all will travel in the region between the cathode and anode with a marked increase of time and path interval, with correspondingly increased probability of ionization.

The magnetic field is appropriately established for the purpose, as by provision of opposite permanent or electromagnetic poles 2|, 2| adjacent and immediately outside of the end plates of the magnetron shown. The magnetic poles are accordingly coaxial with the cathode and set up the magnetic field longitudinally of the cathode or transverse to the direction of normal electron fiow.

It is furthermore preferable to provide a magnetic field of materially greater strength next the anode than next the cathode, with the magnetic field next the cathode as near to zero as possible.

In realization of this desideratum, the magnetic field is preferably established by a hollow core magnet which has the eflect of reducing the strength of the magnetic field adjacent the oathode. The efiect of the reduced magnetic field adjacent the cathode is to prevent as much as possible the return of electrons to the cathode. Upon entering the comparatively magnetic fieldfree-space, an electron returning or inclining to return toward the cathode becomes subject to only one force, that of the electric field urging it back toward the anode.

In Figure 2, indication is given of the magnetic flux lines in cross section by the dots in the outer portion of the central cavity, whereas at the inner portion of the central cavity, such flux lines do not appear in such great number due to the shape of the pole pieces. Likewise in said Figure 2, indication has been given by dotted lines 23 of the gyrating path of several electrons indicative of the influence on the electrons of the magnetic field and the resultant increase in length of such path over the normal straight-line radial path from cathode to anode. It is by virtue of this material increase of path of the electrons which affords greater opportunity for collision of electrons with gas atoms and releasing ions therefrom, charging the ions and causing the ions to bombard the cathode.

We claim: I

1. The hereindescribed method of cathode activation, which comprises emitting electrons from the cathode and simultaneously subjecting region around the cathode to a magnetic field and with said field having greatest intensity remote from the cathode for increasing the electron path.

2. The hereindescribed method of cathode activation comprising emitting electrons from said cathode, producing ions therewith in a magnetic field having greatest intensity remote from the cathode, and bombarding the cathode by said ions.

3. The hereindescribed method of cathode activation comprising thermally activating the cathode, emitting electrons from the thermally activated cathode, spiraling said electrons through a plurality of convolutions remote from the cathode, producing ions therewith, and further activating said cathode by bombardment from said ions.

4. The hereindescribed method of cathode activation of a cathode mounted in an anode cavity, comprising emitting electrons from said cathode toward the anode, applying a magnetic field in the region between said cathode and anode and increasing the electron path substantially more than electron path of normal operation, producing ionsin said magnetic field with said electrons, and bombardingthe cathode by said ions.

5. The hereindescribed method of cathode activation of a cathode mounted in an anode cavity, comprising emitting electrons from said cathode toward the anode, applying a magnetic field in the region between said cathode and anode, of greater intensity next the anode and lesser intensity next the cathode, producing ions in said magnetic field with said electrons, and bombardingthe cathode by said ions. 1

6. The hereindescribed method of cathode activation of a cathode mounted in a cavity of an anode, comprising thermally activating the oathode, emitting electrons from the thermally activated cathode toward the anode, applying a mag netic field to said cavity transverse to the normal direction of fiow or said electrons from cathode to anode and with greater intensity next the anode than next the cathode, thereby causing the electrons to follow a curved path in a region remote from the cathode and promoting ionization, and bombarding the cathode with tons of said ionization.

HOB-E51 A. POE. LESTER, F.

. REFERENCES CITED The following references are of. record in the file of this patent:

' a a lsTATEB RAE Number Name Date 2,115,52E mm et al. New. Am. 26. 1938 Number Nmmbet" ammo