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Патент USA US3084288

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April 2, 1963
J. M. osEPcHuK
Filed Feb. 10, 1960
2 Sheets-Sheet l
T; P\
United States Patent O??ce
John M. Osepehulr, Lexington, Mass, assignor to Ray
theon Company, Lexington, Mass, a corporation of
. Delaware
Filed Feb. 10, End, Ser. No. 7,821
6 Claims. (£1. 315-395)
This invention relates to travelling wave electron dis
?atented Apr. 2, 19%3
is at the same potential as the line and in others it is at
the same potential as the sole. If the beam is projected
into the interelectrode space between the line and the sole
along an equi-potential line V0 and the potential between
the line and the sole is V, the electrical ef?ciency of the
system, 1), is given by the following equation which as
sumes that electrons move over ideal linear trajectories:
The efficiency 1; is further modi?ed by space charge ef
charge devices and, more particularly, to methods and 10 fects and the fact that some of the electrons are captured
means of construction of an M-type backward wave oscil
by the line or the sole, depending on which is at the
lator having novel means to insure proper electron bearn
higher potential. It is generally preferred to ground the
line and the collector and to vary sole potential to change
in travelling wave electron discharge devices, electrical
E and, thereby, tune the oscillator.
waves travelling along a slow wave propagation structure
Heretofore, the problem of preventing electron leak-v
in a tube interact with the ?eld from electrons moving
age past the collector has been met by making the distance
along paths adjacent said structure to produce ampli?ca
between the collector and the sole approximately one half
tion ‘of the travelling wave. The longitudinal component
the distance between the line and the sole, as shown in
of the ?eld of the wave interacts with the ?eld of the
FIG. 1. Such a design insures that substantially all of
electrons travelling along in approximate synchronism
the beam electrons will be collected by the collector and
with it. Some electrons are accelerated and others are
substantially none will leak past the collector. Since the
decelerated resulting in a progressive arrangement of
separation between the line‘ and the sole is, in most ap
electrons in phase with respect to the waves. This process
plications, very small (between .100 and .010 inch), it is,
of mutual interaction continues along the length of the
obviously, dif?cult to construct such a device with such
structure with the result that D.C. energy is given up by
small separation between collector and sole. Further
the electron beam to the wave as radio frequency energy
more, by placing the anode and the sole so very close,
arcing is likely to occur because the potential difference
and, thus, the wave is ampli?ed.
In a travelling wave tube the slow wave propagation
between the anode and sole is usually very large (many
structure may be considered to consist of a number of
thousands of volts). Such arcing is obviously undesir
cells in line. Since such a structure is periodic, the ?elds
able since its immediate and ultimate effect is to introduce
induced in adjacent cells by the propagated wave, have
considerable noise in the output of the device. There
the same spatial distribution but differ uniformly in phase.
fore, it is an object of the present invention to provide a
The electron beam ?eld interacts with the ?elds in the
backward wave oscillator having none of the above-men
cells and this interaction is maximum when the velocity 35 tioned limitations of prior devices.
of the electrons is such that their ?elds encounter the
It is another object'of the present invention to provide
?elds in successive cells in the same phase. In other
an electron collector in an M-type backward wave oscil
words, maximum interaction occurs when the electron
lator for collecting a substantial par-t of the electron beam
velocity coincides with the phase velocity of RF waves
propagating either in the same or in the opposite direction
It is another object to provide such a collector structure
to the direction of RF power ?ow. These RF waves are
wherein equal electrical ?elds are maintained between the
called direct and reverse, respectively, depending on the
collector and the soleand between the line and the sole.
direction of RF power ?ow. Consequently, when the
It is another object to provide a backward wave oscil
beam velocity is equal to the velocity of the reverse wave,
lator in which beam dispersion is ‘substantially greater
the amplitude of the ?elds in the cells increases towards
between the collector and the sole than between the line
the origin of the beam. One type of travelling wave tube,
and the sole.
' sometimes called a backward wave oscillator, produces
it is another object to provide an M-type backward
radio frequency oscillations by the interaction of an elec
wave oscillator in which the magnetic ?eld in the inter
tron beam travelling at substantially the same velocity as
electrode space between the collector and the sole is sub
stantially less than the magnetic ?eld between the line
the reverse wave.
In one type of backward wave oscillator, sometimes
and the sole.
called a type M carcinotron, the electron beam moves in
It is another object to provide a backward wave oscil
crossed electric and magnetic ?elds in the interelectrode
lator tunable by varying sole potential while at the same
space between a wave propagation structure called the
time maintaining the electric ?eld adjacent to the sole
“line,” and an elongated electrode parallel thereto, called
uniform throughout the length of the sole.
the “sole.” The average translational velocity of an elec~
it is a feature of the present invention to provide a
tron in the beam is equal to the ratio of the electric ?eld
travelling Wave type electron discharge device including
E to the magnetic ?eld B. The variation of the oscillator
an elongated structure at one potential for propagating a
frequency with line-to-sole voltage is determined by the
slow wave disposed opposite a similarly elongated con
dispersion characteristics of the beam and the average
ductor at another potential so as to form a substantially
electron velocity. Therefore, frequency depends on both
uniform electric ?eld in the space therebetween, to pro
the electrical ?eld and the magnetic ?eld.
vide electron emitting means at one end of the space and
As the electron beam gives up energy to the radio fre
electron collector means at the other end of the space, to
quency wave in the line, it loses potential energ , how
dispose said device in a substantially uniform magnetic
ever, it maintains the same translational velocity. Since
?eld and to magnetically shield a part of said space in the
the beam electrons lose potential energy, they must move
vicinity of said electron collector.
through substantially higher equi-potential lines of the
It is another feature of the present invention to provide
electrical ?eld E between the line and the sole. Conse
a backward Wave oscillator device including a slow wave
quently, electrons will move either towards the'line or
propagating structure, a collector electrode, and a sole
towards the sole, depending on the direction of the ?eld 70 electrode forming an interelectrode space therebetween
E, and eventually these electrons will be captured by a
and an electron gun projecting electrons into said inter
collector electrode. In some applications the collector
electrode space with means in the vicinity of said collector
electrode for magnetically shielding electrons in that vi
cinity to, thereby, insure collection of electrons by the
collector and to substantially diminish ?ow of ‘electrons
past the collector.
loses potential energy while, nevertheless, the electrons,
will maintain their general translational velocity down the
length of space 7. Since the beam electrons lose energy
they must move through substantially higher potential
lines in the electrical ?eldybetween the line and the sole
electrode, consequently, the electrons will move toward
line 3. Part of the beam under e?icient interaction, there?
‘ It is another feature to electrically couple said electron
collector to the end of said wave propagating structure
thereby forming one end of the interelectrode space and
fore, is collected by the delay line, but generally there is
to dispose magnetic materials thereabout to shield that
always a substantial part of the beam entering the col
‘It is another feature to dispose said device in the mag 10 lector region. In order to insure almost complete col
lection of this latter part of the beam, it has been the
netic ?eld so that the electric ?eld, the magnetic ?eld and
one‘ end from the magnetic ?eld. '
practice in the past todispose col-lector electrode 5 closer
the general direction of motion’ of electrons within the
interelectrode space are mutually perpendicular and to ob-'
to the sole electrode 6 than the structure 3. In fact, it is
tain an RF output from the device at the end of the wave 15 desirable that the space denoted d2 between collector elec
trode 51 and sole electrode '6 be approximately one half
propagating structure nearest the electron gun.
the spacing d1 between structure 3 and sole 6. The pur
Other ‘features and; objects of the present invention will
pose of this is apparent when one considers the relation
be more apparent from the following speci?c description
ship between the potential difference Vm across an in
terelectrode space required to insure complete beam col
20 lection by an electrode, and the dimensions d. It canbe
< FIG. 1 is'a symbolic diagram showing oneprior method
of the prior art and embodiments of the present invention
takeninlconj-unction with the drawings in which:
shown that this relationship is given by the following:
for insuring the collection of electrons by a collector elec
trode in an M-type backward wave oscillator; '
Z FIG. 2 is a symbolic diagram of an MV-type backward
wave oscillator incorporating features of the present in
H v
a '
FIGS. 3 and 4_ are cross sectional views of one embodi
ment‘ of the present invention featuring a circular inter
electrode space and suitable magnetic materials disposed
about one end thereof to‘magnetically shield the space in 30
the vicinity of a collector electrode.
‘ Turning ?rst to FIG. 1 there is‘shown symbolically a
typical‘M-type carcinotron such as employed in the past
. In the above expression, 6 is the charge to mass ratio
of an electron, and B is. the magnitude of the transverse‘
magnetic ?eld in the cavity. Obviously, whenB is ?xed,
the, potential difference required to insure complete col
lection of electrons by an electrode may be decreased by
decreasing the separation d. As already mentioned, this
method is employed in some applications to insure com
plete beam collection by a collector electrode. However,
in such applications all is very small and, of course, d2
demonstrating one prior method for insuring that a sub
stantial part’of the electron beam will ‘flow, to the collector 35 is smaller yet. Since the potential between collector elec
trode 5 and sole electrode 6 is many thousands of volts,
electrode and not past the collector. As shown in FIG. 1
arcing is likely to occur therebetween resulting in numer~.
electrodes are disposed within an envelope 1 and these
ous undesired effects.
include a cathode 2, a slowwave‘structure'or delay line
Turning next to FIG._2 there is shown a symbolic
3, with an accelerating electrode 4 at one end, and a col
lector electrode 5 'at the’ other end. The accelerating 40 representation incorporating features of the present in
of arcing are substantially
electrode 4, the’ structure 3 V and the collector electrode
eliminated. Thestructure shown in FIG. 2 is, similar to‘
are'fre'quently coupled'to'gether and substantially in line
the structure shown in‘ FIG. 1 and includes an envelope
as shown in FIG. 1. Another electrode,- 6, called the’ sole
1-1 enclosing a slow wave propagation structure .12, ac
7 electrode having an elongated shape is disposed within the
envelope 1 opposite structure 3 and collector. electrode 5 45 celerating electrode 13, collector electrode 14, sole elec
trode 15fand cathode 16_ forming interelectrode space 17
tor-form interelectrode space 7. It is convenient to place
with an RF output taken from oneend of structure 12,
structure3 and electrode 5 at ground potential and to
denoted 18. In operation, electrode 14 and structure
place ‘sole electrode 6 substantially. below groundpoten
112, may be electrically coupled together and placed at,
tial, for example, at about minus 7 kv., by coupling to
potential source 8 thereby. creating electric v?eld E1, in 50 for example, ground potential while sole electrode ,15 is
placed at,,for example, minus 7 k.v. by coupling to source
region one, runningfrom the slow'wave structure 3 to the
19, cathode 116 is placed at minus 5 k.v. by coupling to
sole 6. and electric ?eld E2, inregion. two, running from
source 20 and accelerating electrode 13 is placed at minus
collector 5 to sole 6.~ Cathode 2. is preferably placed at a
3 k.v. by coupling to source‘20 as shown in the ?gure.
potential higher than electrode 6, for example, minus
The device is placed in a magnetic ?eld which is perpen
5‘ kv., by coupling to potential source 9'. »Electrons in the 55 dicular
to the electric ?eld created within space 17 and‘
beam. 10, emitted from cathode 2 are accelerated for entry.
also perpendicular to the general motion of electrons
intointerelectrode space 7. 'I‘hisis accomplished by cou
pling cathode 2 and electrode 4 to potential source 10 so
that accelerator electrode 4 is. at the highest potential.
' In operation, a substantially uniform magnetic ?eld is
applied perpendicular to the electric?eld and is repre
sentediin FIG.. 1 by a circle with a dot in its center and
denoted B. Consequently, electronsrernitted‘from,cath
within the space represented by beam 21. Electrons
emitted from cathode 16 are accelerated by accelerating
electrode 13 andproceed down the length of space 17
moving to higher and higher equi-potential lines as energy
is given up from the electron’ beam to the wave in
‘structure 172. VMag’netic shielding pieces 22 and 23 are
disposed substantially contiguously with collector elec
ode 2 are ?rst accelerated towards electrode 4 and then
into space 7, moving down thelength of the space at a 65 trode 14 and one'end of sole electrode 15, respectively,
as shown in the ?gure. These magnetic shielding pieces
velocity, established by the electric ?eld. E1 and the mag
may be, for example, ?at in shape and orientated with
netic ?eld B. The general movement of vthe electrons
their smallest dimension perpendicular to the applied
downfthe length of space 7 is substantially as shown by’
magnetic ?eld so as to afford magnetic shielding in region
mean 10, the electronsproceeding down the ilengthof
the space and dispersing‘ near its end for collection by the 70 two of interelectrode space 17 formed by the collector
electrode 14 and one end of sole electrode 15. Conse
the magnetic ?eld in region two ofrspace 17 is
As already mentioned in'the introduction, the beam .
less than the magnetic ?eld in region one.
electrons moving down the length of space 77 gives up
If the magnetic ?eld in region one is denoted B1 and the
energytolthe radio frequency wave propagated in the
magnetic ?eld in region two is denoted B2, then the ex
slow wave structure 3" and as the beam gives up energy it
collector electrode 5.
75 pression for the voltage di?erential Vmz required to insure
complete collection of the electron beam by the collector
and 45. Consequently, the magnetic flux lines travel
from ring 44 to 45 through the interelectrode space 26.
The magnetic shielding pieces 40' and 41 are preferably
located with a major dimension parallel to this magnetic
?eld. One piece might, for example, be mounted inside
electrode '14 is set forth as follows:
Obviously, if d1 and d2 are equal and of su?icient magni
the ring of sole 25 as shown and another might, for ex
ample, be located between collector electrode 37 and
conductive ring 29 as shown in FIG. 4. The shape and
tron velocity and oscillator frequency, B2 may be varied
orientation of parts forming structure 26 are more clearly
to provide a suitable value of Vmg. This is accomplished
shown in FIG. 4, while the location of the ?ngers are
by employing any number of properly shaped and orien
more apparent in FIG. 3. Rings 27a and 28a supporting
tated magnetic shielding pieces such as 22 and 23 to
these ?ngers are suitably fastened to conductive ring 29
shield region two of the space 17. The shape of the
to form the complete slow wave structure 26. The fasten~
pieces 22 and 23, the number of such pieces and their
ing may, for example, be accomplished as shown in the
orientations may all be varied to achieve the proper 15 referenced patent.
amount of shielding so as to provide a suitable magnetic
Upper and lower cover plates 46 and 47 are provided
?eld B1 in region two of the space. It has been found
for enclosing the structure ‘26, interelectrode space 24, sole
advisable to maintain the dimension “1” of magnetic
25 and cathode 30 so as to form a vacuum seal with con
pieces 22 and 23 greater than 1rd2. It is also preferable
ductive ring 29. Electrical conductors 33, 34, 35 and B6
that the ratio of B2/B1 be less than one third to insure 20 are brought out through terminals 48, 49, 50 and 51 in a
substantially complete beam collection by electrode 14.
suitable electrical feed through 521, which forms a vac
Turning next to FIG. 3 and FIG. 4 there are shown
uum seal with upper plate ‘46 and suitable potentials are
cross sectional views of an M-type backward wave oscil
applied to these terminals for heating cathode 30, ac
lator having a circular interelectrode space 24 and in
celerating electrons emitted therefrom and providing a
corporating features of the present invention. 'FIG. 3 25 uniform electrical ?eld within space 24 while the other
shows a top sectional view BB in which appears a ring
‘parts of the device including upper and lower plates 46
shaped sole 25 concentric with a ring shaped slow wave
and 47, collector electrode 37 and interdigital delay line
propagating structure 26. Structure 26 might, for ex
26 are placed at ground potential.
ample, be comprised of two sets of ?ngers 27 and 28 inter
While the present invention is described herein with
laced and held in place by fastening rings 27a and 28a, 30 reference to a symbolic representation of an M-type back
tude to insure no arcing, and B1 is ?xed at a suitable value
for maintaining the ration E/Bl to obtain a desired elec
from which the ?ngers project, to conductive cylinder 29;
thereby, forming a tortuous path for slow wave propaga
tion. Such a structure is described in considerable detail
in Patent No. 2,890,372, issued June 5, 1959, to E. C.
Dench, and entitled “Travelling Wave Ampli?ers.”
Sole 25 might, for example, have a channel-like cross
sectional shape as shown in FIG. 4. Sole 25 and slow
ward wave oscillator and with respect to a more speci?c
embodiment of such an oscillator including a circular in
terelectrode space for insuring substantially complete
beam collection by a collector electrode, it is to be under
35 stood that the spirit and scope of the present invention
may be incorporated in other type travelling wave devices
to achieve substantially the same or similar results with
out deviating from said spirit or scope as expressed in
wave structure 26 are disposed concentric with each other
so as to provide interelectrode space 24 therebetween. A
the following claims.
cathode 30 and accelerator electrode 31 are inserted be 40
What is claimed is:
tween the open ends of the ring formed by sole 25- and
encloses a heater element 32.
1. An electron discharge device comprising slow wave
Electrical leads run from
cathode 3t}, electrode 31, element 32 and sole 25 to con
ductors 33, 34, 35 and 36, respectively, at the center of
the device.
Structure 26 also forms an open ring, the opening
propagating means at one potential, an elongated elec
trode at another potential disposed with relation to said
propagating means forming an elongated space and bound
45 ing an electric ?eld within said space, electron emitting
means at one end of said space, electron collecting means
at the other end of said space and means producing a
therein being partially opposite the opening in the ring
formed by sole 25 and collector electrode 37 is inserted
in this opening. Electrode 37 may be electrically coupled
to the structure to form one end of interelectrode space
24 referred to as region two in the straight line device
of FIG. 2.
t “i
In operation, a magnetic ?eld from magnet 3-8 is ap
transverse magnetic ?eld in said space substantially uni
form throughout and means at the end of said space
for substantially altering said magnetic ?eld in the vicinity
of said collecting means to thereby insure collection of
a substantial part of said beam by said collecting means.
2. An electron discharge device comprising slow wave
plied to interelectrode space 24 so that electrons emitted
propagating means at one potential, an elongated con
from cathode 30 enter the space and move in a sub 55 ductor at another potential disposed with respect to said
stantially circular path around the space in a counter
propagating means to form an elongated interelectrode
clockwise direction, as shown by the arrow on beam 39‘,
space having a substantially uniform electric ?eld Within,
giving up energy to the RF wave propagated in structure
electron emitting means at one end of said space, elec
26. As the electrons move through space 24 as a beam
tron collecting means at the other end of said space and
and approach collector electrode 37, the beam disperses,
means producing a uniform magnetic ?eld in said space
electrons therein moving to higher potential lines and,
thus, moving closer to the ?ngers of structure 26. By
proper orientation of the magnetic shielding pieces 40 and
41 ?xed to sole 25 and collector 37, respectively, and
adjustment of the strength of magnet 38, substantially
complete collection of the beam by collector electrode 37
can be achieved while at the same time maintaining a
substantially perpendicular to said uniform electric ?eld
and also perpendicular to the general movement of elec
trons within said space and means at the end of said
space for substantially altering said magnetic ?eld in the
vicinity of said collecting means to thereby insure collec
tion of a substantial part of said beam by said collecting
desired radio frequency output from the device. Such
an output might, for example, be taken from ?nger 42
by coupling to coaxial conductor 43 as shown.
propagating means at one potential, an elongated con
In FIG. 4 there is shown cross sectional view AA taken
propagating means to form an elongated interelectrode
through the magnetic shielding pieces 44} and 41 and the
center of the device. In this view a suitable shape for
magnet 38 is shown. The ?eld from the poles of magnet
3. An electron discharge device comprising slow wave
ductor at another potential disposed. with respect to said
space having a substantially uniform electric ?eld within,
electron emitting means at one end of said space, electron
collecting means at the other end of said space, means
38 is conducted through magnetically permeable rings 44 75 producing a magnetic ?eld in said space substantially
perpendicular to said electric ?eld and also perpendicular
vicinity of saidgcollecting. means to' therebye’insure. col
lection of a substantial; partof said beam byL said collect:
to- the“ general» movement of‘ electrons within said-‘fspace'
ing means.
and means .for'magnetically shielding apart‘ of said‘ space
6. An -M-type backward wave oscillator including a
in” the vicinity’ of said electron? collectingimean's- to there?
by insure collectioni of aesnbstantial part‘ of said‘ beam by r 51? slow wave structure, a sole electrode forming an elongated
said’collec'ting means.
4.'An' electron discharge‘ device comprising means for
propagating an electrical’ Wave in-a delay structure, a
conductor displaced from said structure forming an inter»
interelectrode space‘ with said structure, an electron gun
at one end- of said space, an- electron collector at‘ the
other end of said’v space, means-applyingpotentialsto said
structure, sole, gun and‘ collector to induce an electric
electrode space tiliereb’etv'veei'l,v means producing substan 10 field within ‘said space, means producing amagnetic ?eld
tially' crossed electric and magnetic ?elds within said
space, means emitting’ electrons at one'end' of said space,
means‘ collecting electrons at the other end of's‘a‘id space
and- means at said other'end for reducing the" magnitude:
of saidvmagnetic ?eld in the’ vicinity of said‘ electron col
lector to thereby insure collection of a substantial part of
saidi'beami by said» collecting means.’
electrical discharge device comprising slow‘wave'
propagating means" andconducting means having substan
tially elongatedl shapes and disposed with respect to‘ each
other to form an: elongated interelect'rod'e‘ space‘, means
emitting a beam- of- electrons atl'on‘e end of said space,-'
means contiguous vvitlfv said propagating means disposed
at the‘ other end’ of said space for collecting electrons,
means prod?cing crossed electric and magnetic ?elds in
said space and‘ means disposed about said other end of'
said‘space- for‘ magnetically shielding" said space in the
substantially perpendicular to said electricv ?eld and the
general movement- of electrons within said space and
means magnetically shielding a part of said space in the
vicinity of said electron‘ collector to thereby insure col
"lectioxiof a substantial part of said. beam‘ by said collect~
ing means.
References Cited in the ?le of this patentv
20*‘ 2,607,904‘
Lerbs _______ __- _____ _c Aug. 19, 1952
Beck _________________ __ Apr. 1, 1958
25.1 2,871,395
Ciof? _._..'.. ____________ .._ July 22, 1958
Webber __.~__~___- _____ __r_- Sept. 23, 1958
Ciof? _._'- ____________ _____ Jan. 27, 1959
Epsztein _'__...... _______ __ Mar. 311, 1959
Favre _________________ _._ Oct. 3, 1961
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