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Патент USA US2412842

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Dec“ KY, 1946..
P_ L, SPENCER
2,412,842
ELECTRON I C DI S CHARGE CATHODE
Original Fil‘ed Sept. 30, 1941
2 Sheets-Sheet 1
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Dec. 17, 1946.
2,412,842
P. L. SPENCER '
ELECTRONIC DISCHARGE I GATHODE
Original Filed Sept; 30, 1941
2 Sheets~Sheet 2
F7615
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Patented Dec. '17, 1946
2,412,842
UNITED srA'r as PATENT omcai
'
2,412,842~
*
ELECTRONIC DISCHARGE carnonn
Percy L. Spencer, West Newton, Mara, assignor to
Raytheon Manufacturing Company, Newton,
Mass., a corporation of Delaware
Original application September 30, 1941, Serial
No. 412,993. Divided and this application May
" 23, 1944, Serial No. 538,998
1
2 Claims. (Cl. 250-275)
This is a division of my copending application,
Serial No. 412,993, ?led September 30, 1941, for an
improvement in electronic discharge devices.
2
being had to the accompanying drawings, ‘where
in:
Figs. 1 and 2 are diagrammatic representations
This invention relates to an electronic dis
of a magnetron illustrating certain principles of
charge device, particularly of the magnetron type.
operation of my invention;
and to a cathode for such a device capable of sup
Fig. 3 is a cross-sectional view of one embodi
plying large peak values of current.
ment of my novel cathode;
In electronic discharge devices, particularly of
Fig. 4 is a fragmentary view. partly in section
the magnetron type which are called upon to sup
of another embodiment of my nove1 cathode;
ply relatively large peak values of current, various 10 Fig. 5 is an illustration of one type of mag
difiiculties have heretofore existed. The cathodes
netron incorporating my invention, the view in
of such devices have been heated to relatively
Fig. 5 being taken along line 5-5 in Fig. 6; and
high temperatures in an attempt to supply suin
Fig. 6 is a cross-section of the magnetron in
cient thermionic emission to carry such peak
Fig. 5 taken along line 6-6 of Fig. 5, together
values of current. Such cathodes have had an 15 with a. diagrammatic representation of ,a circuit
unusually short life due to the fact that the emis
with which said magnetron may be used.
sive coating with which the cathodes are normal
In Fig. 1 A1 and A: represent two anodes of a
ly coated was rapidly driven oil! from the cathode.
split anode magnetron. C is the centrally lo
This effect was increased by the fact that the load
cated cathode thereof. As is usual in this type
current through the tube tended to overheat and 20 of device, a longitudinal magnetic field is im
burn out the cathode. The arthas resorted to
pressed thereon in a direction at right angles
the use of complicated regulating and protective
to the plane of illustration in Fig. 1. The cath
devices in order to protect the cathodesor such
ode C is connected to a negative potential while
magnetrons from being burned out. However,
the anodes A1 and A: are connected together to
such protective and regulating devices did‘ not 25 a positive potential. Devices of this kind are
substantially affect the loss of coating due to
evacuated to high vacuum conditions in which
high operating temperatures of the cathode which
the gaseous atmosphere plays substantially no
resulted in short life for such cathodes.
part in the discharge. This type of magnetron
An object of this invention is to produce an
when energized sets up high frequency oscilla
electron discharge device of the type which sup 30 tions, creating an oscillating electrostatic ?eld be
plies high peak values of current with its cathode
tween the anode A1 and A2. At one instant of
normally operating at a temperature substantial
time the anode A1 may be more positive than the
ly below that necessary to cause such peak values
anode A2. Under these conditions an electron
of current to be emitted thermionically.
e emitted from the cathode C is accelerated to
Another object is to accomplish the above in 35 ward the anode A1 by the potential thereof. How
a magnetron type ofgcharge device.
ever,‘ the magnetic ?eld causes the electron e to
Another object is to cause such peak values of
travel in a curved path which de?ects the elec—
current to be supplied largely by secondary emis
tron to such an extent that it misses the anode
sion.
A1 and falls upon the anode A2. This imparts
A further object is to devise a cathode in such 40 a negative characteristic to the device, and causes
it to operate as an oscillator.
I
.
a device which will emit large numbers of sec~Under the conditions of operation which I con
ondary electrons without substantial time delay,
template in my invention, in addition to the ac
and which will have a long life.
tion described in connection with Fig. 1, another
A further object is to devise a magnetron which
does not need special regulating and protecting 45 action, as exempli?ed byFig. 2, also takes place.
The electron emission from C causes a swarm S
devices'to prevent the cathode from being burned
of electrons in the space surrounding C. An elec
out.
tron e'. which otherwise might follow the path
A still further object is to devise such a mag
described in Fig. 1, however, encounters inter
netron which is capable of supplying much larger 50 as
ference from the other electrons in the swarm S.
amounts of power than have heretofore been pos
and thus never reaches the anodes A1 or A2, but
sible.
The foregoing and other objects of this inven
tion will be best understood from the following
falls back onto the cathode. The interaction be
tween the electrons in the swarm S may impart
considerable energy to the electron e’ by collision
description oiexempli?cations thereof, reference}555 or otherwise by the time it reaches the cathode
8,419,842
4
C. Assuming the tube to be oscillating, the elec
.
a temperature or thermionic emission. The ends
of the sleeve I are closed by insulating plugs
trons s’ also may receive a considerable amount
of energy directly from the oscillating field be
tween the two’anodes Ar and A2. The magnetic
'I-'|, preferably of alumina. The ends of the
heater coil 8 extend through said plugs so that
heating current may bev supplied thereto. An
?eld tends to give to the electron e' a de?nite .
orbital period in its travel around C, which pe
' electrical connecter tab 8 has one end thereof
riod is substantially equal to the period of oscil
welded to the sleeve I and the other end welded
lation of the voltage appearing between the anodes
to one of the heater ends 8, so that electrical
A1 and A2. This condition permits said oscil
connection may be established to the emitting
lating ?eld to arert its accelerating force upon 10 surface of the cathode.
‘
the electron e’ in the proper phase and at the
Instead of making the cathode as illustrated in
proper time to successively impart energy to said
Fig. 3, it can take a variety of other forms‘, one
of which is illustrated in Fig. 4. In this ?gure,
Due to the above e?ects, electrons of the a’
instead of using round wire, the sleeve I is wound
. electron.
-
type can be'made to fail upon the cathode C with 15 with a ?at ribbon 3’, also preferably of tantalum.
considerable speed and energy, which may be
This ribbon, for example, may be .0005 inch thick
substantially above 100 volts. If the cathode C
and .050 to .100 inch wide. Such a ribbon may be
is made so as to be a good secondary electron
initially coated with emitting materials, as de
emitter, then such impinging electron may give
scribed above, and wound upon the sleeve I with
rise to the emission of several additional electrons. 20 about half of each turn of the ribbon overlapping
The current due to secondary emission may be
the preceding turn. Here again the coating may
.made several times the current due to simple
be baked in air as described above, and the coat
thermionic emission at the operating temperature
ing scraped from the outside of the cathode struc
of the cathode. In addition, when the tube is
ture, leaving the top surfaces 4’ of the ribbon
called upon to supply greatly increased peaks of 25
current, then the secondary electron emission
material 3' bare.
'
The cathode structures as described above pos
can be made to increase enormously to carry such
peak currents without substantial time delay. In
other words, such a device can be made to oper
sess the property of being excellent secondary
electron emitters, particularly from the scraped
tantalum surfaces, as well as good thermionic
ate as an electron multiplying arrangement in 30 emitters from the exposed oxide surfaces. The
which the normal thermionically-emitted elec
tantalum has a tendency to reduce the barium
trons are multiplied to give an increased supply
oxide, liberating small amounts of barium on the
of electrons which in turn are again multiplied
by a similar-process.
'
surface of the coating which tends to give excel
lent electron emission. Also the barium so lib
‘
In accordancewith my invention I utilize such 35 erated tends to coat the bare surfaces of the tan
secondary emission to supply a- large part of the
talum, making it an excellent secondary electron
peak currents which such a device may be called
emitter. Even without any barium coating, tan
upon to supply. For this purpose I prefer to
talum in itself is a good secondary emitter.
construct the cathode of the discharge device in
Cathodes of'the type as illustrated in Figs. 3
a special form, as shown for example in Fig. 3. 40 and 4 may be incorporated, for example, in a
The cathode illustrated consists of a sleeve I
magnetron of the type as illustrated in Figs. 5
and 6. The magnetron therein illustrated com
made of some suitable material, such as tantalum
or nickel. In one example of this cathode the
prises an envelope I I which is preferably made of
cylinder was about six millimeters in diameter,
a block of conducting material, such as copper.
and about fifteen millimeters long. Thesleeve 45 This block forms the anode structure of the mag
is coated, except for the end portions thereof,
netron. Said block has hollow end sections
with a layer 2 of a mixture of barium and stron
which are covered by end caps I2 and I3, likewise
tium carbonates in a nitrocellulose-amylacetate
of conducting material, such as copper; Between
binder. ‘In some instances I prefer to add from
the hollow end sections of the block I I is a central
one to one and one-half per cent. of borax in‘ 50 bridging portion I4. The portion I4 is provided
with a central bore I5 within which is supported
order to decrease the'evaporation rate of the
substantially at the center thereof a cathode I0
coating material during operation. The sleeve so
which, as pointed out above, is preferably of the
coated is baked in air at a temperature of about
type as illustrated in Figs. 3 and 4. The cathode
400° F. Thereupon a winding 3, preferably of
tantalum wire, is wound over said coating. In 55 I0 is supported by a pair of lead-in conductors
I6 and ‘I1 fastened respectively to the ends 0 of
the embodiment mentioned above, this wire has
th cathode structure, and sealed through glass
consisted of tantalum .004 inch in diameter,
seals I8 and I9 mounted at the outer ends of pipes
spaced .003 inch between adjacent turns. In
20 and 2| hermetically fastened within the walls
orderto retain the winding upon the cathode and
of the block I I adjacent the upper and lower hol
to insure good electrical contact with the under
60 low end sections.
lying sleeve, the ends 5 of the wire 3 may be
welded directly to the sleeve I. After the wire
3 has been wound upon the cathode, the cathode
is again coated with the coating material de
scribed above and again baked in air at a tem
perature of about 400° F. Thereupon the coat
ing is scraped off the outside of the cathode
structure. leaving the top surfaces 4 of the wire .
3 bare. The baking of the carbonate coatings
in air not only drives 01! the binder material, but 70
also- largely converts the carbonates into the
A plurality of slots 22 extend
radially from the central bore I5 to within a short
distance of the outer wall of the block I I.
when such a magnetron is placed between suit
able magnetic poles 23 and 24 to create a longi
tudinal magnetic?eld and the device is energized,
oscillations are set up whose frequency and conse
quently whose wave length are determined pri
marily by the dimensions of each of the slots 22.
It is also desirable that the value of the magnetic
?eld is such as to impartto the electrons travel
ling around the cathode an orbital frequency sub
stantially equal to the frequency of said oscilla
the turns of which are coated with insulating
tions. Moreover the voltage applied to the anode
material, is inserted within the sleeve I for the
purpose of enabling the cathode to be raised to 75 structure should be of the proper- value to cause
oxides. ‘A heater coil 6, preferably of tungsten,
2,412,842
5
such oscillations to occur and for the desired peak
value of current to ?ow between the cathode and
anode structure. The oscillations produced in
cathode to a temperature at which some therm
ionic emission occurs. This thermionic emission
may emanate largely from the oxide coating
which is exposed to the discharge area, through
the spaces between the coiled winding on the out
side of the cathode. Some of this‘ thermionic
‘emission may occur from the surface of the coiled
the'slots 22 reinforce each other and may be led
out from the tube by means of a coupling con
ductor 25 fastened to the cen ral bridge portion
I4 in the central bore 15 betwe 11 two of the slots
22. The coupling conductor 25 leads out from
winding itself, particularly if the metal thereof
the magnetron through a glass seal 21 at the
has a thin film of barium coated upon it. How
outer end of a pipe 25 likewise hermetically fas 10 ever, during operation the electrons which fall
tened through the wall of the envelope II adja
upon the cathode largely impinge upon the bare
cent the' upper hollow portion thereof.
metal surface of the coiled external winding, and
The magnetron may be connected in any suit
liberate the secondary electrons therefrom. The
able circuit, one of which is shown diagrammati
oxide coating between the turns of this winding
cally in Fig. 6. In this circuit the cathode is sup 15 is largely shielded from such electron bombard
plied with heating current from the secondary
winding 28 of a heating transformer 29 whose pri
mary winding 30 is adapted to be connected to a
ment, and thus forms very little, if any, tendency
for such bombardment to drive any of the oxide
coating from the cathode. However, such coat
ing is always available to supply barium for the
suitable source of alternating current. Inter
posed in the circuit of a. secondary winding 28 is 20 initial electron emission as well as barium which
a switch 3| and a current-regulating resistance
tends to increase the secondary electron-emitting
32. A source of potential 33, which in a, practical
qualities of the metal surface of the external
embodiment may be of the order of 12,500 volts,
winding. An additional advantage of the con
is connected between the envelope ll, constitut
struction which I have illustrated is that the sur
ing the anode, and the lead-in wire I 6 for the 25 faces from which the secondary electrons are
cathode l0. Interposed in the circuit for the
emitted are directly electrically connected to the
source 33 is an interrupter or “chopper” 34 which
sleeve I by having the ends 5 welded thereto. In
interrupts the circuit so that the magnetron gen
this way the current can flow through a direct
erates short pulses of high intensity high fre
low resistance metallic path to the very surface
quency oscillations. The frequency of interrup 30 at which the electrons are being liberated. This
tion may be of the order of two thousand times
is in contrast to the usual oxide-coated cathode
a second. The duration of each energization of
in which the current must ?ow through the rela
the tube may be of the order of a half a micro
tively high resistance oxide coating before it
second.
reaches the emitting surface. In this way the
I have constructed a. considerable number of 35 present cathode structure is much more effective
devices substantially as shown in Figs. 5 and 6
and e?icient.
and embodying a cathode as illustrated in Fig. 3,
By my present invention I have been enabled to
as well as the various parameters recited herein.
construct practical magnetron devices which have
Tubes of this kind were designed to produce oscil
generated enormous peak quantities of micro
lations of a wave length of about three centi 40 wave length power entirely outside of the range
meters. In such a tube I have found that during
of anything which has heretofore been practicable
each half micro-second during which the device
with such devices.
was energized, the anode current rose substan
Of course it is to be understood that this in
tially instantaneously to a value of about twelve
vention is not limited to the particular details as
amperes and continued throughout at this value 45 described above as many equivalents will sug
for substantially each period of energization.
gest themselves to those skilled in the art. For
The average anode current throughout the entire
example, it may be possible to incorporate oer
time was of the order of about fourteen milliam
tain fundamental features of this invention in‘
peres.
_
other devices which are called upon to supply
In starting the operation of such a device, the 50 high peak values of current, particularly in con
cathode was raised to a temperature at which
nection with micro-Wave generators, It is ac
enough thermionic emission occurred to initiate
cordingly desired that the appended claims be
the operation of the device, such emission being
given a broad interpretation commensurate with
of the order of milliamperes and being much less
the scope of the invention within the art.
than that required to supply peak currents of the
What is claimed is:
order of amperes. However, as pointed out above,
when operation started, peak currents of the order
1. An electric discharge device including spaced
anode and cathode electrodes the surface of one
of which electrodes is covered in part with loose
of amperes were supplied. Furthermore, after
the operation of the device had begun, it was
and outwardly projecting particles of material
possible to open the heating circuit by the switch 60 subject to being removed therefrom by the elec
3|, and the device continued in operation with no
trostatic forces between the two said electrodes,
discernible difference, the tube continuing to
means to prevent the removal of said particles of
generate oscillations in the same Way and to sub
material, said means comprising an electrostatic
stantially the same degree as before the opening
shield comprised of a helically wound wire coil
of said circuit. Also under these conditions, when
having a coil-turn spacing and extending in con
the pole pieces 23 and 24 were deenergized so as
tact for its full length with said electrode having
to remove the magnetic ?eld on the device, the
the projecting particles, said‘ coil being of highly
current to the anode structure fell to zero and
refractory non-emissive metal and being electri
the operation of the device ceased. This is in
cally connectedto said electrode having the pro
strong contrast to the usual magnetron device in 70 jecting particles, said coil having its convolu
which if during operation the magnetic ?eld is
deenergized, the current between the cathode and
tions exposed in front of said electrode having
the projecting particles and in front of said pro
the ‘anode structure rises rapidly.
jecting particles, said coil providing for the loca
As pointed out above, the heater 6 is supplied
tion thereon of the electrostatic lines of force in
with heating energy so as to initially raise the 75 front of\said electrode surface having the pro
9,412,849
jecting particles and
front or said particles in
preference to the loca ion of said lines of force
on the said electrode surface having the project
ing particles, and said coil providing for the pas
sage between the convolutions thereof of elec
trons to and from said electrode surface having
the projecting particles.
2. An electric discharge device comprising a
her overlying and exposed in front of and c!
, tending from end to end of the surface of said .
, electron emissive surface and in contact there
cathode electrode provided with an electron emis
sive surface consisting of relatively loosely ad -10
herent material and an electrostatic shield mem
with throughout the length 01' said shield mem
ber and electrically connected to the electrode,
said shield member consisting of high refractory
non-emissive metal and having a plurality of
openings therethrough for the free passage of
electrons to and from the electrode surface.
PERCY L. SPENCER.
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