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Патент USA US3046454

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July 24, 1962
E_ T_ DQwNlNG ET AL
3,046,444
MAGNETRONS
Filed April 28, 1959
33
F/G. I
26
EÜWÁRÜ
GEORGE
gy
Y
Í/VVE/VTÜRS
r [70W/VIN@
E SMITH
A rroR/VEY
United States PatentO MICC
3,046,444
Patented July 24, 1962
2
used which have a greater temperature coefficient of ex
3,046,444
pansion than ceramic, there is a pronounced tendency for
Edward T. Downing, Winchester, and George F. Smith,
binding to occur between the ceramic washer of the prior
art and the cathode 'sleeve which is inserted within the
MAGNETRONS
Newtonville, Mass., assignors to Raytheon Company,
a corporation of Delaware
Filed Apr. 28, 1959, Ser. No. 809,409
10 Claims. (Cl. S15-39.51)
ceramic Washer. Such binding is undesirable, since it is
necessary, in order to prevent bending or other distortion
of the cathode assembly, that the cathode be free to slide
in the ceramic support during thermal expansion and
This invention relates to a magnetron-type electron dis
charge device, and, more particularly, to means for sup
porting a cathode assembly in a magnetron-type electron
discharge device.
contraction.
Because of the relatively short path presented by the
ceramic washer of the prior art between the cathode and
the pole pieces (and the anode block), the thermal losses
Magnetron electron discharge devices vare well known
by conduction are relatively high, thus increasing the
which comprise a cathode structure, an anode ystructure
heater power requirements correspondingly.
spaced from and surrounding said cathode structure and
In accordance with this invention, an elongated ceramic
incorporating several cavity resonators, and -also means
member of relatively small outer dimension and cross
for establishing a magnetic field transverse to the elec
sectional area is inserted in the tail end of either the
tron path between the cathode and anode structures.
cathode sleeve or an extension thereof. A metal or
When a proper voltage is applied between the cathode and
ceramic washer is attached to the other end of the ceramic
anode structures of such a device, and when the magnetic 20 member and this washer is bonded to the magnetic pole
field is adjusted to an appropriate value relative to the
pieces or anode. This cathode support has several ad
electric field created by 4the yaforesaid voltage, oscillatory
vantages over the cathode support of the prior art, pre
energy is generated whose frequency is determined pri
viously referred to. 'Ihe ceramic rod has a small radial
marily by the geometry of the physical elements compris
dimension, being less than that of the cathode sleeve, or
ing the cavity resonators.
at least smaller than that of the cathode end shields, if
-In some applications, magnetrons are subjected to
any. Consequently, little or no electron-emissive mate
severe vibration and shock during operation. ln mag
rial evaporating from the active surface of the cathode
netrons of the prior art, wherein the cathode is supported
will be deposited upon lthe ceramic. Inasmuch as the
at a single point, the cathode assembly may be con
‘ceramic rod can be made of considerable length with
sidered mechanically to be a cantilever beam. When 30 out unduly complicating tube design, the voltage gradi
such a device is subjected to shock and vibration, move
ent in the ceramic rod may be relatively small and the
ment of the cathode invariably occurs, whereupon un
leakage path `along the ceramic rod may be compara
desirable amplitude and frequency modulation of the
magnetron output takes place. If the free end of the
cathode assembly is supported in some manner, move
ment of the cathode assembly is reduced, together with
the accompanying undesirable modulation.
tively long. Since the ceramic rod is positioned inside
the cathode sleeve, binding between the rod and the
35 cathode sleeve-owing to thermal expansion and con
traction of the rod and sleeve-will be minimized and
the necessary capability for relative motion of the cathode
One type of cathode support previously resorted to
Vand cathode support is maintained. A material, such as
consists of a ceramic washer placed around the free end
molybdenum, which has substantially the lsame thermal
of the cathode assembly and attached to one of the mag 40 >coefficient of expansion as the ceramic rod, will not bind
netron pole pieces. This cathode mounting arrange
ment, although an improvement over the cantilever-type
cathode mounting arrangement, has certain disadvan
tages. There is a considerable voltage gradient along
the ceramic washer of the prior art, particularly in the
case of high voltage tubes, because of the relatively short
leakage path along the insulating washer interposed be
tween the anode and cathode; instability resulting from
with the rod; furthermore, any tendency for the rod to
fit too loosely in the cathode »sleeve will be prevented.
`Since the ceramic rod is of considerable length and of
relatively small cross-sectional area, thermal losses from
' the cathode by way of conduction are reduced; more
over, any variation in the degre of contact resistance
between the cathode and the ceramic rod will constitute
a correspondingly smaller portion of the total thermal
excessive current leakage over the insulating washer, or
resistive path, whereby the effect of contact variation is
even tube breakdown owing to arcing, often occurs. Al 50 reduced. It has been found that considerable reduction
though this trouble may be reduced somewhat by in
in heater power required for starting the magnetron can
creasing the diameter of the insulating washer, this can
be achieved with the cathode support Aaccording to the in
be yachieved only be reducing the lsize of the poleV piece
vention.
'
in the region of the washer or by increasing the diameter
of the pole piece assembly. If the pole piece is cut
away, the reluctance of the pole pieces is increased, with
`a subsequent reduction in magnetic field strength. If,
on the other hand, the ydiameter of the pole piece yis in
incorporating Ia cathode support according to the inven
creased, the bulk of the magnetic assembly is unduly
tion; and
Other objects and advantages of this invention will be
come apparent -as the description thereof progresses, ref
erence being had to the accompanying drawing wherein:
FIG. 1 is a central cross-sectional View of a magnetron
,
increased and, in fact, the entire tube may have to be 60 FIG. 2 is a detail View illustrating «a manner of modi
made larger to accommodate such an enlarged magnet
fying the cathode support shown in FIG. 1.
assembly.
Moreover, the ceramic washer of the prior art is eX
posed to electron-emissive material evaporated from the
Referring to the drawing, refernce numeral 10 desig
nates an electron discharge device of the magnetron type
having an anode structure 12 of well known construction
cathode during tube operation. This electrically-conduc 65 4which includes a cylindrical envelope member 13 of an
tive material, which gets past the cathode end shields, is
electrically-conductive material and a plurality of radially
deposited upon the ceramic washer and forms an `elec
disposed, inwardly extending anode mem-bers 14 in the
trically-conductive film on the washer. This film eventu
ally causes an electrical short circuit between the cathode
and the anode (which is electrically connected to the mag
netic pole pieces).
When certain cathode materials, such as nickel, are
form of electrically-conductive vanes attached to mem
ber 13. Each pair of adjacent anode members, together
70 with ¿tha-t portion of the cylindrical member included
therebetween, at least partially define a cavity resonator;
these resonators are electrically intercoupled in the nor
3,046,444
3
4
of construction, materials and processes described, as
many equivalents will suggest themselves to those skilled
together -adjacent their innermost ends by straps 16 in
in the art. It is accordingly desired that the appended
order to prevent spurious oscillation of the magnetron in
claims be given a broad interpretation commensurate
undesired modes. The upper and lower ends of the tube
are shielded hermetically by means of respective pole Ul with the scope of the invention within the art.
What is claimed is:
shoes 18 and 19 of magnetic material attached to anode
mal manner. Alternate anode members 14 are connected
cylinder 13. The pole shoes 18 and 19 are connected
to pole pieces 21 and 22, respectively. A U-shaped mag
net 24, partially shown in -FIG. l, is held a-gainst the pole
pieces 21 and 22 for providing the necessary magnetic
ñeld. Output energy may be coupled from the magnetron
to a wave guide 26 by means of a slot, not shown, cut in
the anode cylinder 13 between any two adjacent anode
members 14. The anode cylinder l13 may include a
ilanged portion 13’ to which the wave guide 26 may be
attached. An exhaust tip-olf 27 is connected toa disoidal
member 28 which, in turn, is connected to lower pole
piece 22; this tip-olf provides a means for exhausting
1. In a magnetron having an anode structure and hav
ing a cathode whose longitudinal axis is coincident with
the longitudinal axis of said magnetron, an elongated
electrically insulating member arranged parallel to said
longitudinal axis and slidably supporting said cathode
at one end thereof, said member having substantially
smaller cross wise dimensions than said one end of said
cathode and an element attached to said member, said
element extending substantially perpendicular to said
longitudinal axis and being supported by said anode
structure.
2. In a magnetron having an anode structure and a
cathode, «an elongated electrically insulating member
pole piece 22 serves to protect the exhaust tip-olf 27 20 slidably supporting said cathode at one end thereof, said
member having substantially smaller cross wise dimen
from damage.
sions than said one end of said cathode, and a discoidal
A cathode structure 30 is positioned concentric with
element attached to said member and supported by said
anode structure 12 and includes a cathode sleeve 31 which
the magnetron tube 10. A member 29 attached to lower
may, for example, be made of nickel and which is pro
vided with integral end shields 31a and 31b. The por
tion of sleeve 31 facing the extremities of the anode
members 14 is coated with an electron-emissive material,
in the well known manner.
The cathode structure 30
anode structure.
3. In a magnetron having an anode structure and a
cathode, means for supporting said cathode at both ends
thereof with respect to said anode structure, said means
for supporting including an elongated electrically insulat
ing member movably joined to said cathode adjacent one
further includes a heater element 32 positioned within
the cathode sleeve 31 and connected at one end thereto. 30 end of said member, said member having substantially
smaller cross wise dimensions than said cathode and an
The other end of heater element 32 is attached, as by
element attached to said member adjacent the other end
welding, to a heater lead-in wire 33 which passes out of
of said member supported by said anode Structure.
the tube envelope through a tubular member 34 fastened
4. In a magnetron having an anode structure and a
at one end to the upper end of cathode sleeve 31. The
cathode, means for supporting said cathode at both ends
heater lead-in wire 33 may be supported within the tubu
thereof with respect to said anode structure, said means
lar member 34 by electrically insulating beads 35. A
for supporting including an elongated electrically insulat
short metal tube 36 is attached to upper pole piece 21
at one end, while a glass or ceramic seal 37 is attached
ing member slidably engaging said cathode adjacent one
end of said member, and an element attached to said
to the other end of tube 36. A metal thimble 38, which
is brazed to a metal disk 39, is sealed to glass seal 37 40 member adjacent the other end of said member.
5. In an electron discharge device having a magnetic
and »to the outer periphery of tubular member 34. A
field-producing structure, an anode structure and a cathode
glass bead 40 `at the upper end of tubular member 34
for directing electrons in the region between said cathode
completes the hermetic seal »for the cathode structure.
and said anode structure, an elongated electrically insulat
The cathode-heater supply voltage may be furnished by
way of circuit leads, not shown, which may be connected 45 ing member slidably engaging said cathode adjacent one
end of said member, and an element attached to a portion
to the heater lead-in wire 33 and the disk 39, respectively.
of said magnetic field-producing structure and to said
A cathode sleeve extension in the form of a short tube
member adjacent the other end of said member.
42 and made, for example, of molybdenum, is brazed to
6. In an electron discharge device having a magnetic
the lower end of cathode sleeve 31. Slots 43 may be
provided in the periphery of tube 42 to prevent possible 50 field-producing structure, an anode structure and a
cathode for directing electrons in the region between said
deformation of the tube during brazing owing -to difter
cathode and said anode structure, an elongated electrically
ences in thermal coefficients of expansion of the nickel
insulating member slidably engaging said cathode adja
cathode sleeve and the molybdenum tube. The cathode
cent one end of said member, said member having an
44 securely attached at one end to metal washer 45 and 55 outer dimension less than that of said cathode, and an
element attached to a portion of said magnetic field-pro
slidably mounted at the other end to the tubular exten
ducing structure and to said member adjacent the other
sion 42 of the cathode sleeve so as to support the cathode
and prevent radial movement thereof. 'I‘he metal washer
end of said member.
7. In an electron discharge device having an assembly
45 is sealed to lower pole piece 22 and is provided with
apertures 46 to permit evacuation of the tube. The 60 including an anode structure and at least a portion of a
support structure 30 includes an elongated ceramic rod
washer 45, instead of being made of metal, such as kovar,
may be made of ceramic, particularly where a slightly
larger leakage path between anode and cathode is desir
able. A metal washer is somewhat more convenient,
magnetic ñeld-producing structure, and a cathode for di
recting electrons in the region between said cathode and
said anode structure, said cathode including end shields
extending outwardly therefrom, an elongated electrically
however, since a metal washer may be sealed more readily 65 insulating member slidably engaging said cathode adja
cent one end of said member, said member having an
to the metal pole piece 22 than a ceramic washer.
outer dimension less than that of said cathode end shields,
As indicated in FIG. 2, it is possible to insert the
and an element attached to a portion of said assembly
ceramic rod 44 of the cathode support structure 30 di
and to said member adjacent the other end of said mem
rectly into the cathode sleeve 31, provided that the
cathode sleeve is made of a substance, such as molybde 70 ber.
8. In an electron discharge device having an assembly
num, which (l) has approximately the same thermal
including an anode structure and at least a portion of a
coefficient of expansion as the ceramic Irod and which
magnetic field-producing structure, and a cathode for di
(2) will not cause binding to occur between the cathode
recting electrons in the region between said cathode and
sleeve and the elongated ceramic rod 44.
This invention is not limited to the particular details 75 said anode structure, an elongated electrically insulating
5
3,046,444
member slidably engaging said cathode adjacent one end
of said member, said member having an outer dimension
less than that of said cathode, and an element extending
substantially perpendicular to said member and attached
to a portion of said assembly and to said member adja
6
structure including a tubular extension, `an elongated elec
trically insulating member disposed along the longitudinal
axis of said magnetron and having one end slidably in
serted Within said tubular extension, and an element dis
posed substantially perpendicular to said member »and
cent the other end of said member.
9. In a magnetron having an anode structure and a
cathode structure and means for producing a magnetic
ñeld transverse to `said region, said anode structure and
at least a portion of said magnetic field-producing means
ber adjacent the other end thereof, the lateral extremities
of said member being disposed nearer said longitudinal
forming an integrally mounted assembly, said cathode
pansion substantially equal to that of said member.
structure including a tubular portion, an elongated elec
trically insulating member disposed along the longitudinal
axis of said magnetron and having one end slidably in
serted within said tubular portion, and an element dis
posed substantially perpendicular to said member `and at
tached -to `a portion of said assembly and to said member
adjacent the other end thereof, the lateral extremities of
said member being disposed nearer said longitudinal axis
than the lateral extremities of said cathode structure.
20
10. In a magnetron having an anode structure and a
cathode structure and means for producing a magnetic
ñeld transverse to said region, said anode structure and
at least a portion of said magnetic field-producing means
attached -to a portion of said assembly and to said mem
axis «than the lateral extremities of said cathode structure,
said tubular extension having a thermal coefficient of ex
References Cited in the ñle of this patent
UNITED STATES PATENTS
1,666,010
2,199,956
2,412,824
2,414,605
2,424,805
2,444,418
2,698,913
Hawadier ____________ __ Apr. 10, 1928
Marden ______________ __ May 7, 1940
MacArthur ___________ __ Dec. 17, 1946
Okress _______________ __ Ian. 2l, 1947
De Walt _____________ __ July 29, 1947
Bondley ______________ __ July 6, 1948
Espersen ______________ __ Jan. 4, 1955
OTHER REFERENCES
Microwave Magnetrons, Collins, page 792 relied upon,
forming an integrally mounted assembly, said cathode 25 McGraw-Hill, 1948,
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