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Патент USA US3050667

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Aug. 21, 1962
3,050,657
G. M. BRANCH, JR
SLOW WAVE STRUCTURES
Filed Jan; 12, 1955
2 Sheets-Sheet 1.
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Gar/and M. Branch?/ .,
His Attorney
Aug.21,1962
3,050,657
G. M. BRANCH, JR
SLOW WAVE STRUCTURES
2 Sheets-Sheet 2
Filed Jan. 12, 1955
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United States Patent 0 MICC
,
,
3,050,657,
Patented Aug. 21, 1962
2
1
of the vacuum enclosure of the traveling wave tube and
3,050,657
SLOW WAVE STRUCTURES
Garland M. Branch, Jr., Schenectady, N.Y., assignor to
General Electric Company, a corporation of New York
Filed Jan. 12, 1955, Ser. No. 481,450
11 Claims. (Cl. 315-—3.6)
therefore can be easily cooled and adjusted for optimum
operation of the traveling wave tube.
It is therefore an important object of this invention to
provide improved slow wave structures.
Another object of this invention is to provide improved
slow wave structures for use in traveling wave interaction
This invention relates to helical slow wave structures
and, while this invention may be incorporated in a large
number of ‘diiferent types of apparatus, it is, by way of
example, particularly described in connection with travel
ing wave interaction devices generally identi?ed as travel
devices wherein the electron beam velocity can be easily
and conveniently controlled throughout the interaction re
gion to effect optimum operation of the device.
Another object of this invention is to provide an im
proved slow wave structure for use in a traveling wave
interaction device wherein the combined e?ects of elec
ing wave tubes.
tron bunching and electron interaction with a traveling
\In a traveling Wave tube utilizing a helix slow wave
structure, an electromagnetic Wave is caused to follow 15 electromagnetic wave are easily and conveniently ef
fected.
the turns of the helix so as to result in a reduced velocity
It is also an object of this invention to provide a
slow wave structure having in corporated therein stabiliza
tion means having high heat dissipating characteristics
of the helix and at a velocity so that interaction will
take place between the electromagnetic Wave and the elec 20 and convenient reproducibility.
It is also an object of this invention to provide a
trons in the electron beam. Customarily, where it is de
slow wave structure for use in a traveling wave interaction
sired to amplify the electromagnetic wave energy, the
device which has a substantially ?eld free drift region
electrons in the electron beam have an average velocity
the effective length of which can be easily and convenient
which is greater than the velocity of the electromagnetic
of electromagnetic wave propagation along the helix axis.
An electron beam is caused to travel parallel to the axis
wave along the helix axis so that energy is transferred 25 ly varied.
In accordance with an important aspect of this inven
from the electron beam to the electromagnetic wave.
tion there is provided a slow wave structure comprising
The resulting transfer of energy from electrons in the
a plurality of helices. Between each of these helices there
electron beam to the electromagnetic wave results in a
is provided at least one coupling helix which is oriented
decrease in the electron beam energy and a consequent
velocity and density modulation of the electron beam. In 30 to transfer electromagnetic wave energy between each
of said plurality of helices.
order to effect maximum energy transfer from the electron
Other important objects and aspects of this invention
beam to the traveling wave, it would be desirable to be
will become apparent from the following speci?cation
able to control the electron beam velocity at various
and claims when taken in connection with the ?gures of
points along the helix by applying different direct current
potentials to discrete regions of the helix. In convention 35 the drawing wherein FIG. 1 illustrates an example of
al helix traveling wave tubes this is not possible since the
a traveling wave interaction device incorporating this
helix is ‘highly conductive.
A solution to this problem which has been advanced,
invention; FIGS. 2 through 6 illustrate diagrams useful
in explaining the theory of operation of this invention;
consists of breaking the helix up into a number of sec
tions and coupling energy ‘from one of the helices to a
second section or helix by means of the velocity and
‘and FIGS. 7 through 9 illustrate examples of other em
bodiments of this invention.
FIG. 1 illustrates a traveling wave interaction device,
density modulation of the electrons in the electron beam
hereinafter referred to as a traveling wave tube which
or alternatively to use two electron beams, one as an
includes an electron gun 10 consisting of electron emit
energy supplying beam and the other as ‘an electro
magnetic wave coupling beam.
‘
Systems such as those above-described tend to be cum
bersome and relatively ine?‘icient; however, slow wave
structures of the type hereinafter described as part of
this invention provided a convenient means of trans
ferring electromagnetic wave energy between separate
helices which can then be maintained at different poten
tials. Therefore, in accordance with this invention it is
possible to maintain the beam potential at an optimum
value and at the same time effectively and e?’iciently
transfer electromagnetic wave energy vbetween the helix
sections.
In addition to being able to maintain the electron beam
at an optimum velocity it is possible in the practice of
ting cathode 11, accelerating anode 12, and heater 13
45 which is energized ‘by power supply 14. The heater makes
electrical connection to cathode 11 at junction 15 to pro
vide the low potential connection through lead 16 to power
supply 17. Electrons from cathode 11 follow the gen
eral beam path 18 and are collected by collector 19 which
is connected by lead 20 to power supply 17, at a lower
potential point than accelerating anode 12 in order to
e?ect deceleration of the electrons in beam 18. Solenoid
21 provides a magnetic ?eld substantially parallel to the
beam path to focus the beam along the desired path from
55. the cathode 11 to the collector 19.
The traveling wave tube is provided with two helices
within glass or ceramic vacuum enclosure 22. Helix 23
is provided with an input lead 24 through which electro
this invention to effect a substantially ?eld free drift re
' magnetic ‘wave energy can be easily coupled. Helix 23
gion between the helices so that electron bunches formed 60 is severed at point 25 to provide a gap 26 along the elec
as a result of interaction of the electromagnetic wave with
tron beam which extends between point 25 and point 27
the electrons in the beam can drift and then recombine in
on helix 28. Helix 28 is provided with. an output lead
proper phase with a second section of helix to further in
29 from which ampli?ed electromagnetic wave energy can
be extracted. The accelerating anode and the helix 23
crease the energy transfer from the electron beam to the
65 are maintained at the same potential through lead 30
electromagnetic wave on the slow wave structure.
Another characteristic difficulty in the construction
and operation of traveling wave tubes is that of stabilizing
which makes adjustable connection to power supply 17
while helix 28 can be maintained at the same potential,
or, as herein illustrated at a slightly higher potential
and backward traveling waves at the operating frequency. 70 through separate lead 31.
As thus far described, this tube provides substantially
In accordance with another aspect of this invention the
the tube ‘by attenuating undesired frequency components
attenuating structure is formed on an external portion
no coupling between helix 23 and helix 28 for an electro
3,050,657
3
4
magnetic wave, except through the relatively inetl'icient
under idealized conditions is transferred from one line
means of the electron beam 18. In order to transfer a
maximum amount of electromagnetic wave energy from
helix 23 to helix 28 there is provided coupling helix 32.
to the other line every quarter of a space heat wave length
N
(1)
Helix 32 is Wound in an opposite sense to helices 23 and 5
28 and has substantially the same helix pitch angle. Helix
32 is further provided with an adjustable potential source
33. In order to attenuate undesired electromagnetic
wave energy components which tend to render the travel
ing wave tube unstable there is provided an attenuating
means 34 which may, for example, consist of an aquadag
coating ‘or a coating of other high loss material which is
applied to the outer surface of the vacuum enclosure 22
and between a portion of the coupling helix 32 and the
electron beam 18. Attenuators 34’, which may for ex
ample consist of rods of high loss material are placed
between the turns ‘of coupling ‘helix 32 to attenuate back
Thus it may be seen that a space beat wave length, which
will be further described in subsequent paragraphs,
amounts to two complete cycles of power transfer between
lines 1 and 2.
The manner of power transfer will become more ap
parent from a consideration of FIG. 3. It is well known
that if coupling exists between two transmission lines, such
that electromagnetic wave energy traveling in one of them
induces an electromagnetic wave in the other line that
travels in the same direction, the power originally fed to
one of the lines will gradually transfer to the other. Then
the
reverse process starts, i.e. the power tends to transfer
ward traveling wave energy, particularly at the operating
back to the original line as has been described in connec
frequency. It will be noted that this attenuator is iso~
lated from the electron beam and therefore is not subject 20 tion with FIG. 2. The two requirements are that the in
dividual transmission lines have substantially the same
to electron beam saturation. In addition the attenuator
34' is easily cooled and may be varied to obtain optimum
operation.
velocities of propagation and that the coupling provides
a forward traveling wave.
FIG. 3 illustrates the normal coupling between two
The traveling wave tube illustrated in FIG. '1 is operated
by applying the necessary operating potentials so as to 25 conductors of different transmission lines wherein there
is shown the electric and magnetic vectors E and H and
effect an electron beam ?owing between cathode 11 and
the
resulting Poynting vector S which determines the di~
collector 19 wherein the average electron velocity is
rection of wave energy propagation along the transmission
slightly greater than the velocity of an electromagnetic
line. The differential induced electric and magnetic ?elds
wave propagated along helix 13. The manner of com
dB and dH over the distance dZ are shown. Here the
30
puting these velocities and designing a helix conductor
resulting wave travels in the opposite direction as shown
with the proper pitch to achieve maximum e?icien‘cy and
by dS so that the coupling illustrated in FIG. 3 does not
optimum electron beam coupling is Well known in the art.
result
in what is generally termed spacial beating and from
An electromagnetic wave is applied to input lead 24
which the term “beat wave length” is derived.
land is caused to be propagated along helix 23. The wave
Thus, if two helices are wound in the same direction
energy interacts with the electrons in- the electron beam 35
there is relatively loose coupling therebetween and sub
to absorb energy therefrom. When the electromagnetic
stantially no energy is transferred therebetween; however,
wave energy reaches the region where the coupling helix
if a pair of concentric helices are wound in opposite
overlaps the input helix 23 electromagnetic wave energy
senses as illustrated in FIG. 4, spacial beating does occur
is induced into the coupling helix. As will be hereinafter
and as a result of the relatively strong coupling there
described if the overlap between coupling helix 32 and 40 between
there is a highly e?icient energy transfer.
input 'helix 23 is one-quarter or an odd number of quarter
In FIG. 4 it will be noted that a wave impressed on the
space beat wave lengths of the coupled electromagnetic
outer helix, line 1, travels down and to the right. Where
energy, there will be a complete transfer of the electro
the pitch angle is relatively small, a wave is induced on the
magnetic wave energy on helix 23 to the coupling helix 32
inner helix, line 2, that travels up but again progressing
so that at point 25 there is substantially no electromagnetic
toward the right. This backward coupling over an incre
wave energy on helix 23 since all of this energy has been
mental distance, together with forward coupling in the
transferred to coupling helix 32.
overall structure results in spacial beating and strong cou
In a like manner the electromagnetic wave energy is
propagated along coupling helix 32 and is subsequently
transferred to output helix 28 where it further interacts
with the electrons in the electron beam so that an en
hanced output is obtained from output lead 29.
,
pling between the oppositely wound helices. Thus, it
may be seen that it is possible to exchange power between
the two helices and that the inner helix may be the travel
ing wave tube helix in the vacuum enclosure while the sec
ond or coupling helix may readily be oriented outside of
‘It is apparent, then, that there is provided a means for
the vacuum enclosure.
transferring electromagnetic wave energy from a ?rst
FIG. 5 illustrates the instantaneous amplitudes of the
helix to a second helix without forming any direct current 55 electromagnetic waves on a pair of coupled helices. The
connection therebetween and in such a manner that the
coupled wave is always 90 degrees out of phase with the
severed section of the helices do not have to be specially
induced
wave, as is well known, so that the secondary
terminated and can be operated at the correct direct cur
effect of the induced wave coupled back to the ?rst helix
rent potential to obtain optimum operation of the travel
gives a 180 degree phase shift to subtract power from the
ing wave tube.
original wave.
Before describing the additional features of this inven
FIG. 5 illustrates the beat wave envelopes 36 and the
tion, it is considered desirable in order to obtain a corm
instantaneous waves 37 and 38. From these illustrations
plete understanding thereof to discuss the phenomena
it is apparent that under idealized conditions there is a
which occurs when energy is transferred between the
transfer of electromagnetic energy from one helix to the
helices. FIG. 2 illustrates two conducting lines which 65 other helix every one-quarter of a space beat wavelength
for purposes of this discussion may be considered repre
so that, referring back to the illustration of FIG. 1, if
sentative of one of the helices within the vacuum en
closure and of the coupling helix, respectively. For ex
ample, line 1 can be considered to represent helix 23
and line 2 to represent helix 32. Curve 35 illustrates the
manner in which electromagnetic wave energy or power
is transferred between the helices when they are properly
oriented and so spaced as to effect a power transfer there
between.
It will be noted that substantially all of the energy, 75
there is an overlap of one-quarter or an odd number of
quarter wavelengths between coupling helix 32 and input
helix 23 there will be, under idealized conditions, no
power on helix 23
nation is necessary
coupling helix 32.
energy at terminal
on output helix 28.
at point 25 so that no special termi
and there will be maximum power on
In a like manner, no electromagnetic
39 of helix 32 and maximum energy
In the foregoing discussion of FIGS. 2 to 5 the descrip
3,050,657
5
6
tion has been quali?ed with the statement that these rela
tions apply under idealized conditions. It should be
clearly understood that the effective transfer of electro
magnetic wave energy over broad bands is possible in
any properly designed system and that the losses intro
ing wave tube structure illustrated in FIG. 1 to effect the
duced, for example, by helix resistance, space charge
objects of this invention. It is noted, and it can easily
be shown that coaxial helix couplers introduce very small
re?ections over extremely wide bandwidths such as, for
example, frequency ranges in the order of 5 to l, Where
such wide band acceptance is desired. For example, a
traveling wave tube of the type illustrated in FIG. 1 can
effects and the effects peculiar to the material and form.
readily be designed to operate e?iciently and effectively
of the vacuum envelope, merely change the well known
over a frequency range from approximately 300 to 1500
design parameters and do not alter the fundamental con
cept of ‘being able to transfer electromagnetic energy be— 10 megacycles.
The attenuator 34 illustrated in FIG. 1 as has been
tween helices which are otherwise insulated for direct
previously mentioned, may consist of any lossy material
currents and voltages.
such as an aquadag coating which can be easily and con
FIG. 6 further illustrates the particular phenomena
veniently sprayed on the outer surface of the vacuum
accompanying this form of broad band coupling and,
speci?cally, it is a plot of the amplitude of the axial 15 enclosure 22. Thus, by placing theattenuator external
to the vacuum enclosure, the amount of attenuation can
component of the electric ?eld associated with a traveling
electromagnetic wave. FIG. 6a illustrates a plot of the
be easily controlled, is more easily cooled, is relatively
free from saturation effects due to the action of the elec
two energy modes which are characteristic of two co
tron beam, and furthermore is in a strong electromagnetic
axial helices wound in the opposite sense wherein there
?eld as a result of substantially all of the power being
is strong cross coupling therebetween. The inner and
transferred to coupling helix 32. Aquadag coating 34
outer helices are diagrammatically indicated by the circles
extends a small distance over the regions where the inner
located along the Zero axis line and curve 40‘ illustrates
one mode of energy propagation and curve 41 illustrates
helices are terminated; however, it does not extend be
yond the outer ends of the coupling ‘helix since to do so
a second mode of energy propagation.
Modes 40 and 41 are propagated along the helices in 25 would result in ine?icient transfer of power to the
coupling helix and from the coupling helix back to the
a direction substantially perpendicular to the surface of
inner helix. Thus, attenuator 34 stabilizes the tube
the drawing and at different velocities. Mode 40 is
characterized by in-phase currents of approximately equal
against regeneration and oscillation by damping spurious
oscillations and the electromagnetic waves associated with
amplitudes in the two helices and mode 41 by substan
tially 180 degree out-of-phase currents. Thus, for ex 30 these oscillations which are re?ected from the output ter
mination or load and propagated back along the slow wave
ample, if one helix, say the inner helix 28, is terminated
structure of the tube input.
by an open circuit such as open circuit at point 27, so
Very often, the re?ected electromagnetic waves at the
that no current can ?ow in helix 28 at point 27, an
operating frequency are at such a high power level that
approximately equal mixture of the two modes is excited
when an electromagnetic wave is propagated in the outer 35 it is necessary to provide additional attenuation such as
lossy rods or members 34’ which are herein shown as
helix, for example, coupling helix 32.
It is interesting to note that the conditions prevalent
being placed between the turns of the coupling helix 32.
Substantially all of the electromagnetic wave energy at
at point 27 and throughout the gap 26 in FIG. 1 are
the operating frequency passes through the coupling helix
generally illustrated in FIG. 6b by curve 42 which illus
trates the distribution of electromagnetic ?eld across the
and therefore any re?ected wave energy, which would tend
tube when substantially all of the electromagnetic wave
to render the interaction device unstable, can be absorbed
energy is on the outer helix. It will be seen that under
by this easily cooled and controlled attenuating means.
these conditions there is a very strong electromagnetic
As has been previously mentioned the quarter space
?eld between the helices and having a peak centered over
‘beat wave length overlapping section of coaxial cross
the outer coupling helix 32 and that there is substan—
wound double helices provides a very wide-band re?ec
tially no electromagnetic ?eld in the region 43 between
tionless transition between the inner helix 23 and the
the wires of the inner helices. This intermediate region
coupling helix 32 in a relatively‘ short physical distance.
43 is the region through which the electron beam passes
The inner helix, which is effectively severed, can have its
and the distribution of the electromagnetic ?elds im
input and output sections, 23 and 28, respectively, oper
mediately suggests that there is established a substantially
ated at different voltages to provide optimum gain and/ or
?eld free drift region in gap 26 which is further enhanced
e?‘iciency without the customary necessity of introducing
by the shielding e?ect of the high loss coating 34. Elec
long tapered attenuators near the severed ends. Such
trons in the beam can drift through this ?eld free region
attenuators interfere with the interaction between the slow
and bunch in accordance with the velocities imparted
wave on the inner helices and the electron beam and re
thereto by the interaction of these electrons with the
duce the e?iciency as well as the gain of the tube.
electromagnetic wave on helix 23.
It is apparent, from FIGURE 6, that by increasing the
Again considering FIG. 6, it is noted that the two
diameter of the outer or coupling helix the ?eld strength
modes are then propagated down the coaxial structure
in the proximity of the electron beam due to the electro
until an elapsed phase angle of one of the modes is 180
magnetic wave energy on the coupling helix will decrease.
degrees greater than that of the other mode at which 60 If it is desired to design a relatively narrow band pass
point the two modes now interfere to effectively cancel
coupling helix it is only necessary to utilize a coupling
helix having a relatively large diameter compared to the
the currents on the outer helix as illustrated by curve
44 in FIG. 6b. Thus, if the outer helix is discontinued
diameter of the inner helices.
at this point the wave propagates along the inner helix
As has been previously mentioned, in connection with
alone and the radial frequency or electromagnetic energy 6 the discussion of the curves in FIG. 6 of the drawing, it
has been e?ectively transferred from the outer helix to
is theoretically possible to transfer all of the electromag
netic wave energy from the inner helix to the coupling
the inner helix.
A consideration of the energy distribution in curve 44
helix such that there is substantially no electromagnetic
of FIG. 6b immediately suggests that substantially all
?eld in the vicinity of the electron beam and consequently
of the energy on the helices is within the vacuum en
the electromagnetic wave is completely decoupled from
closure so that there is strong interaction between the
electron beam and the electromagnetic wave energy prop
the electron ‘beam. Under ideal conditions an outer helix
which has a diameter approximately one and one-half
agated along the inner helix.
In view of the foregoing ‘it is readily apparent that the
above mentioned teachings can be applied to the travel
times the diameter of the inner helix is su?icient to de
couple completely the traveling wave from the beam.
75 Thus, the attenuator inside the coupling helix and out
3,050,657
7
8
side of the inner helix gap 26 as well as the greater di
therefore the drift time can be varied by varying the
length of the gap, the length of drift tube 53 and/or the
potentials applied to the coupling helix or the drift tube
or both. Energy is transferred to the helix 46 and from
ameter and lower axial impedance of coupling helix 32,
reduces the direct coupling between the beam and the
outer helix so that a substantially ?eld free drift region
26 is provided between the two helices 23 and 28. Thus
the helix 47 by the same mechanism as hereinbefore de
scribed in connection with the transfer of energy from an
electrons which have interacted with the electromagnetic
wave on helix 23 ‘are permitted to drift through region 26
and bunch or group in accordance with the velocities im
inner helix to an outer helix.
The advantages of this
method of coupling are readily apparent in that they
reduce the number of glass-to-metal seals that must be
parted thereto by the electromagnetic Wave. That is,
those electrons moving slower than the actual velocity of 10 formed in order to extract energy from the inner helix
the electromagnetic wave are accelerated and those mov
and require less complicated terminating structures at the
ing faster than the electromagnetic wave are decelerated
so that there is a grouping or bunching in the gap or drift
ends of the helices within the vacuum enclosure.
FIG. 8 illustrates an alternative construction that can be
utilized to effect el?cient attenuation of undesired modes
space 26.
If the drift region 26 is made su?'lciently long and 15 and to obtain some degree of electron bunching. In FIG.
helix 28 is of the proper length the electron bunches will
8 there is shown input helix section 55 and output helix
have completely formed and will interact in proper phase
section 56 separated by lossy helix section 57 so that there
with the electromagnetic ‘wave which is transferred from
is an effective gap for radio frequency currents in the
the coupling helix 32 back to the helix 28 so as to result
in a considerably enhanced electromagnetic wave output
from lead 29 as a result of this combined effect. The
intermediate region de?ned by the lossy section of helix
57. The lossy section 57 can be ‘formed, for example, by
efficiency and gain of the tube.
since lossy helix section 57 provides a relatively good
applying a high loss material to a wire helix. Effective
length of the drift region 26 can be initially adjusted so
radio frequency electromagnetic wave energy coupling
as to effect the proper spacing between the helices 23 and
between helices 55 and 56 is effected by coupling helix
28 and, in addition, power supply 33 is provided so that
58 and some stabilization is provided by the lossy section.
the potential of the coupling helix can be varied and 25 An attenuator for the operating frequency re?ected elec
the effective length of the drift region controlled for
tromagnetic wave energy can be placed in juxtaposition
optimum bunching and phasing of these bunches with the
to the helix 58 and therefore be in a strong electromag
electromagnetic wave. What has just been described
netic wave energy region and yet be easily cooled and
then, amounts to recombining the density modulated
varied for optimum tube operation. It is apparent that
beam at the end of the drift space 26 in proper phase
the structure herein illustrated is not suited for operating
with the electromagnetic wave energy transmitted through
conditions where it is desired to operate the input helix
the coupling helix so as to result in enhancement of the
section and the output helix section at different potentials
Under certain conditions it may be necessary or desira
ble to have a relatively small gap between the ends of
direct current path between sections 55 and 56.
FIG. 9 illustrates a plurality of helix sections 59, 60
the helices 23 and 28. If this is the case, the necessary
attenuation can be obtained by applying aqua-dag coating
and 61 which are coupled by coupling helix sections 62
and 63.
to other regions of the outer surface of vacuum en
Potential leads 64, 65 and 66 are coupled to
helices 5'9, 60 and 61, respectively, and provide a means
for maintaining these helix sections ‘at the proper potential
for optimum operation of a traveling wave tube. It is
apparent that this multiple helix structure can be pro
closure 22 and using a short section of coupling helix to
transfer some of the wave energy to the outer surface so
as to provide a strong electromagnetic ?eld in the region
of the attenuating means. Alternatively a coupling helix
of lossy material can be used which couples some of the
vided with any one or all of the other features hereinto
‘fore described in order to provide a multigap structure
energy to the outer helix from one or more of the inner
having substantially ?eld Ifree drift regions between the
helices but in which there is no physical inner helix gap‘. 45 respective inner helices. Thus, there is provided an effec
It is ‘also readily apparent that Where it is desirable a
tively periodic traveling wave tube structure wherein there
relatively long traveling wave tube having a number of
‘are provided several beam voltage steps to maximize the
such drift regions can be provided so that the tube will in
tube ef?ciency.
effect consist of a plurality of drift regions 26 with associ
In view of the foregoing, it is readily apparent that
ated coupling helices 32.
50
among the adjustable parameters, whose optimum values
FIG. 7 illustrates an alternative embodiment of this in
can be determined by theory or easy experimentation,
vention wherein electromagnetic wave energy is intro
include the length and pitch of the input helix, length
duced to inner helix 46 through coupling helix 45 and is
and pitch and relative diameter of the coupling helix
extracted from inner helix 47 by means of coupling helix
including the length of the drift section and the length
48. Coupling between helices 46» and 47 is elfected by 55 and pitch of the output helix. Thus, it is possible to design
means of outer coupling helix 49. This embodiment is
an efficient and effective traveling wave tube incorporating
provided with stabilizing aquadag coating 50 and an at
this invention which can be operated over a wide fre
tenuator 51. Since the coupling helix 49 is somewhat
quency band or a relatively limited frequency band
remote from drift region generally indicated by 52, under
depending on the desired service and the band previously
some conditions it may be desirable to provide a drift 60 mentioned may be placed anywhere within a large portion
tube in the gap between helices 46 and 47. This drift
of the radio frequency spectrum. In addition, it is ap
tube 53 consists of a conducting tubular member through
parent that this invention can be applied to interaction
which the electron beam can pass so that it will be in a
completely ?eld free region.
In addition there is pro
vided a tap '54 so that the drift tube 53' can be maintained 65
at the desired potential and so that the effective length of
the drift tube can be conveniently varied. It is apparent
that this drift tube can be used in combination with any
or all of the embodiments previously shown and described
in connection with the illustration of FIG. 1 and that the 70
accompanying electron beam forming means, magnetic
?eld and potential supplies are not shown in FIG. 7
merely as an aid in reducing the complexity of this de
scription.
Thus, it is apparent that the ?eld free drift region and
devices using low density annular electron beams and to
any of the many other applications of slow wave structures.
In view of the foregoing, it is readily apparent that this
invention is subject to a large number of modi?cations and
variations and that the examples herein described are
considered to be representative only. Therefore, it is
intended to include in the appended claims all such modi
fications and variations as come within the ‘true spirit and
scope of this invention.
What I intend to claim and protect by Letters Patent
of the United States is:
1. In a traveling wave interaction device including
means for producing a beam of electrons within a vacuum
3,050,657
10
‘enclosure, a ‘slow wave structure comprising ?rst and
second helical sections oriented within said enclosure and
in energy transferring relationship with the beam of elec
trons, the adjacent ends of said helical sections being in
spaced, longitudinal relation with respect to the propaga
tion of high frequency waves, a coupling helix placed out
side the vacuum enclosure and oriented in overlapping
relation with the adjacent ends of said helical sections to
tron beam to de?ne a gap between the helices and along
the electron beam, means applying electromagnetic wave
energy to said ?rst helix and means for extracting electro
magnetic wave energy from said second helix, a coupling
helix overlapping at least a portion of the adjacent ends
of said ?rst and second helices to transfer electromagnetic
wave energy across the gap and between the helices, said
coupling helix having a pitch substantially equal in mag
transfer electromagnetic wave energy between said helical
nitude to the pitch of said ?rst and second helices but
sections, said coupling helix having a pitch substantially
equal to the pitch of said helical sections but opposite in
opposite in direction, a lossy material surrounding said
direction, a ?rst attenuator oriented between the coupling
helix and the interior of the vacuum enclosure and a
second attenuator coupled to the coupling helix to stabilize
the interaction device, whereby heat energy in the attenua
tors is easily dissipated and the amount of attenuation is
easily controlled to effect idealized operation of the inter
action device.
2. In a traveling wave interaction device including
gap and oriented ‘between said coupling helix and said
electron beam whereby electrons crossing said gap are in
a substantially ?eld free region and can bunch in accord
ance with the velocities imparted to the electrons as a
result of interaction of the electrons with the electro
magnetic wave energy on said ?rst helix, means for
applying a potential to said coupling helix to control
the effective length of the ?eld free drift region so that
said bunches interact in phase with the electromagnetic
means for producing a beam of electrons, a slow wave
wave energy transferred to said second helix by the cou
structure comprising ?rst and second helical sections
oriented in energy transferring relationship with the elec
pling helix to result in enhanced gain and e?iciency of
said interaction device.
7. In a traveling wave interaction device including
the electron beam, a coupling helix overlapping the ad
means for producing a beam of electrons, the combina
jacent ends of the ?rst and second helical sections to 25 tion comprising ?rst and second helical sections of con
transfer electromagnetic wave energy across the gap and
ducting material positioned in energy exchanging relation
between the helical sections, said coupling helix having
with said beam of electrons and having the adjacent ends
a pitch substantially equal to the pitch of said ?rst and
thereof positioned in spaced longitudinal relation with
second helical sections ‘but opposite in direction whereby
respect to‘ the path of the beam and the propagation of
the electrons crossing said gap are in a substantially ?eld 30 high frequency waves and a coupling helix extending be
free region and can bunch in accordance with velocities
tween said helical sections and overlapping the adjacent
imparted to the electrons as a result of electron interaction
ends thereof, said coupling helix having substantially the
and with electromagnetic wave energy on said ?rst helical
same pitch as said ?rst and second helical sections but
tron beam to de?ne a gap between the helices along
being wound in the opposite direction to provide for the
section, said gap being of proper length so that said
bunches interact in phase with electromagnetic wave 35 transfer of energy ‘between said ?rst and second helical
energy transferred to said second helical section by the
sections through said coupling helix.
coupling helix whereby the gain and ef?ciency of said
8. In a traveling wave interaction ‘device including
interaction device are enhanced.
means for producing a beam of electrons, the combina
3. In a traveling wave interaction device including
tion comprising ?rst and second helical sections of con
means for producing a beam of electrons, a slow wave 4:0 ducting material positioned in energy exchanging relation
with said beam of electrons and having the adjacent ends
structure of the type de?ned by claim 2 wherein a con
ductive member is oriented in said gap and in proximity
thereof positioned in spaced longitudinal relation with
respect to the path of the beam and the propagation of
high frequency waves ‘and a coupling helix extending be
4. In a traveling wave interaction device including 45 tween said helical sections and overlapping the adjacent
ends thereof by an amount corresponding substantially
means for producing a beam of electrons, a slow wave
to an odd number of one-quarter wave lengths at the space
structure of the type de?ned by claim 3 wherein a poten
heat wave lengths of the electromagnetic energy to be
tial is applied to the conductive member to control the
coupled, said coupling helix having substantially the same
effective electrical length of the ?eld free drift region.
pitch as said ?rst and second helical sections but being
5. In a traveling wave interaction device including
Wound in the opposite direction to provide for the trans
means for producing a beam of electrons, at slow wave
fer of energy between said ?rst and second helical sections
structure comprising a ?rst helix and a second helix
through said coupling helix.
oriented in energy transferring relationship with the elec
to said electron beam to effect a more completely ?eld
free drift region within the gap in the interaction device.
tron beam to de?ne a gap between the helices and along
9. In a traveling ‘wave interaction device including
the electron beam, a coupling helix overlapping the ad 55 means for producing a beam of electrons, the combina
tion comprising ?rst and second helical sections of con
jacent ends of said ?rst and second helices to transfer elec
tromagnetic wave energy across the gap and between the
ducting material positioned in energy exchanging rela—
helices, said coupling helix having a pitch substantially
equal in magnitude to the pitch of said ?rst and second
tion with said beam of electrons ‘and having the adjacent
ends thereof positioned in spaced longitudinal relation
with respect to the path of the beam and the propagation
of high frequency waves, a coupling helix extending be
tween said helical sections and overlapping the adjacent
helices but opposite in direction, a lossy material surround;
ing said gap and oriented between said coupling helix and
the electron beam whereby beam electrons crossing said
gap are in a substantially ?eld free drift region and can
ends thereof, said coupling helix having substantially the
bunch in accordance with the velocities imparted to the
same pitch as said ?rst and second helical sections but
means for producing a beam of electrons, a slow wave
structure comprising a ?rst helix and a second helix
structure comprising ?rst and second helical sections, said
?rst and second helical sections being wound in a ?rst
75 direction and oriented in energy transferring relation
electrons as a result of interaction of the electrons with 65 being wound in the opposite direction to provide for
the transfer of energy between said ?rst and second helical
the electromagnetic wave energy on said ?rst helix, said
sections through said coupling helix and means maintain
gap being of proper length so that said electron bunches
ing said coupling helix at a direct current potential dif
interact in proper phase with the electromagnetic wave
ferent than the ‘direct current potential of said ?rst and
energy transferred to said second helix by the coupling
second helical sections.
helix whereby the gain and ef?ciency of said interaction
10. In a traveling wave interaction device including
device ‘are enhanced.
means for producing a beam of electrons, at slow wave
6. In a traveling wave interaction device including
oriented in energy transferring relationship with the elec
3,050,657
1i
12
ship with the beam of electrons and a coupling helix
potential being of such a value as to maintain said input
wound in a sense opposite to that of said ?rst and second
helix at a direct-current potential to minimize the cou
helical sections vand oriented to transfer electromagnetic
pling loss between both of said helices with regard to
wave energy between said ?rst and second helical sections,
the growing wave portion of said electromagnetic Wave.
said coupling helix having substantially the same pitch as
References Cited in the ?le of this patent
said ?rst ‘and second helical sections and having a position
coaxial With and overlapping with respect to the adjacent
UNITED STATES PATENTS
ends of said helical sections.
2,584,308
Tiley ________________ __ Feb. 5, 1952
11. A traveling-Wave tube ampli?er comprising an elec
Hansell _____________ __ Mar. 11, 1952
tron gun including a cathode maintained ‘at a predeter 10 2,588,832
2,616,990
Knol et al. __________ __ Nov. 4, 1952
mined reference potential for producing an electron
2,623,193
Bruck ______________ __ Dec. 23, 1952
stream, means for directing said stream along a predeter
2,636,948
Pierce ______________ __ Apr. 28, 1953
mined path, a collector electrode disposed opposite said
2,660,689
Touraton et a1 _________ __ Nov. 24, 1953
electron gun to intercept the stream electrons, an input
2,733,305
Diemer ______________ __ Jan. 31, 1956
helix maintained at a ?rst predetermined potential with
2,782,339
Nergaard _____________ __ Feb. 19, 1957
respect to said reference potential and disposed about said
2,793,315
Haeif et al. _________ __ May 21, 1957
path adjacent said electron gun for propagating an elec
2,804,511
Kompfner _________ __ Aug. 27, 1957
tromagnetic Wave at a predetermined velocity, said pre
determined velocity being small in comparison to the
velocity of light, a principal helix maintained at a second
predetermined potential with respect to said reference
potential and electromagnetically coupled to said input
helix and disposed between said input helix and said
collector electrode for propagating said wave, said ?rst
2,806,177
2,811,673
Haeif ______________ __ Sept. 10, 1957
Kompfner __________ __ Oct. 29‘, 1957
2,814,779
Mendel ______________ __ Nov. 26, 1957
668,168
Great Britain ________ __ Mar. 12, 1952
FOREIGN PATENTS
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