DE1264622B - Electrostatic focusing arrangement for bundled guidance of the electron beam of a travel time tube - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

Number: File number: Registration date: Display day:

HOIj

German class: 21 g -13/17.

1264 622
R26884IXd / 21g
7th December 1959
March 28, 1968

The invention relates to an electrostatic focusing arrangement for the bundled guidance of the electron beam of a time-of-flight tube over a larger one Distance by means of periodically successive electrodes arranged coaxially to the electron beam.

It is known that an electron beam of considerable length and current density because of the repulsive forces between the electrons gradually widens in the course of the beam path, unless precautions are taken is taken to prevent such beam broadening. It is also known that in transit time tubes, z. B. klystrons and converting field tubes, a magnetic one for the bundled guidance of the electron beam or electrostatic focusing arrangement. In some cases it is there very desirable or even necessary, the beam diameter at least along that path practical to keep constant on which the beam is influenced at high frequencies. You can get one practically ensure constant beam diameter by creating a strong constant magnetic field, whose lines of force run parallel to the beam axis. Such a beam focusing means however, a considerable effort in terms of weight and cost. Therefore, it is preferable to do one periodically to use effective, magnetic or electrostatic focusing arrangement in which the Electron beam through a series of alternately oppositely directed magnetic or electrostatic Focusing fields passes through. Such arrangements have the advantage of being small Weight and low operating costs. However, the previously known electrostatic focusing arrangements are practicing do not exert any uniform forces on the ray along its path and therefore cannot generate constant beam diameter. Rather, they generate a beam with periodic constrictions and with enlargements of the beam diameter lying between these constrictions, whereby the constrictions (and consequently also the enlargements of the beam diameter) have the same periodicity like the focusing arrangement.

Furthermore, a time-of-flight tube is known whose electron beam is driven by a strong axial magnetic field is focused and passes through an electrode arrangement that is shaped and with such DC potentials it is applied that an approximately sinusoidal potential distribution is created along the beam path. These sinusoidal potential distribution causes a periodic acceleration and deceleration of the electron beam and changes to the electrostatic focusing arrangement accordingly

for bundled leadership

of the electron beam of a time-of-flight tube

Applicant:

Radio Corporation of America,

New York, N.Y. (V. St. A.)

Representative:

Dr.-Ing. E. Sommerfeld, patent attorney,

8000 Munich, Dunantstr. 6th

Named as inventor:
Frank Emelio Vaccaro,
Wieslaw Wojciech Siekanowicz,
New Brunswick, NJ (V. St. A.)

Claimed priority:
V. St. v. America December 16, 1958
(780783)

Space charge density that is used to amplify a signal modulated onto the beam. at one embodiment of this known time-of-flight tube is the sinusoidal potential distribution a series of identical, coaxial to the electron beam arranged, ring-shaped electrodes are generated, which alternate are at positive or negative DC potentials with respect to ground. The sinusoidal potential distribution has practically no influence on the beam focusing, which is exclusively due to the axial magnetic field is effected.

The invention is based on the object of an electrostatic focusing arrangement for bundled Guiding the electron beam of a time-of-flight tube over a longer distance by means of coaxial to indicate the electron beam arranged, periodically successive electrodes that the Avoids the disadvantages of the known focusing arrangements mentioned at the beginning and a practical one constant beam diameter along the part of the beam path that is important for the interaction guaranteed.

This is achieved according to a first possible embodiment of the invention in that the one another the same, annular disk-shaped electrodes (diaphragms) applied to such DC potentials

809 520/531

are that at the distance of the focusing period , electrodes lying at a high DC potential (V ₁₁ ) alternate with sets of electrodes whose DC potentials decrease gradually towards the respective set center electrode lying at a low DC potential (V ₁ ) so that they decrease along the beam path results in a potential distribution which per focusing period at least approximates the equation

or there

the equation

x \ =

suffices where | x | the distance from the median plane

of the respective set center electrode, V (x) is referred to as equal to 25;

The length of the focusing period is about 1.7 times the beam diameter.

A further development of the above-mentioned second embodiment of the invention is thereby characterized in that the axial length of the more hollow cylindrical electrodes is approximately 0.8 times the beam diameter and the largest inside diameter at the ends of these electrodes about 1.6 times that Beam diameter and that the thickness of the

ίο annular disc-shaped electrodes no larger than is about 0.03 times the beam diameter.

The best approximation to the ideal potential distribution is achieved when each of the focusing electrodes is equipped with a grid which runs transversely to the electron beam. Of the Electron beam can be at the beam generator end of the focusing arrangement by known means, for example through an electrode system, which has a parallel electron path (parallel beam) or a convergent electron trajectory (convergent bundled electron beam) ensures to be introduced.

F i g. 1 is a schematic representation of the potential profile on which to explain the invention

F i g. 2 shows the potential profile between two adjacent grids in FIG. 1;

tion of the lattice potentials -y = - ;

H ρ

F i g. 4 shows the normalized perveance - "- as

y "m

Function of the grid potentials -— ■ ;

the equation "Vl / or there V (x) X v _L

potential in distance | χ |, α ² = 2.335 -10 ⁶ γ ² and J

the beam current density in A / m ² is _Fig . ₃ shows the normalized beam current -f-

A second embodiment of the invention ^BB / ",

thought is characterized in that in the ab- 30 under the conditions according to FIG. 2 arranged as the radio stand of the focusing period
A high DC potential (V _H ) lying, annular disk-shaped electrodes with the same opening diameter (diaphragms) alternate with a low one
Equal potential (V ₁ ) lying, essentially more 35
hollow cylindrical electrodes which, in particular F i g. 5 shows a partially schematic diagram

with regard to their respective pulling position to the electron beam of a focusing arrangement according to a turned inner wall, designed so that embodiment of the invention; along the beam path results in a potential distribution, F i g. 6, 7 and 8 are sectional views of FIG

the electrode arrangements which can be optionally used per focusing period at least approximately 4 °, the

instead of the electrode arrangements in FIG. 5 can be set;

F i g. 9 shows the potential profile for the electrode arrangements according to FIG. 6, 7 and 8; Fig. 10 shows a klystron with two cavity resonators in section, in which the electron beam enters the focusing arrangement in a converging manner;

Fig. 11 shows a section for the beam generator part of a klystron, which is constructed in the same way as that of FIG. 10, but in which the electron beam enters the focusing arrangement as a parallel beam.

When designing tubes in which periodic electrostatic fields are used to keep the beam diameter constant, it is desirable to obtain a maximum current I _m and a maximum perveance P _n with a minimum constriction of the electron beam. The smallest possible change in the beam diameter is therefore desirable in order to keep the beam current intercepted by the electrodes as small as possible and to achieve maximum amplification for a given beam current.

The generation of a parallel electron trajectory and thus a constant beam diameter is illustrated in FIGS. 1 explains in which schematically a series of grids G with infinite

Xo =

the equation

x [=

suffices, in which | χ | the distance from the center plane of the respective hollow cylindrical electrode, V (x) das

Equal potential at a distance | χ f, a ² = 2.335 · 10 ~ ⁶ y * and J is the beam current density in A / m ² .

According to a further development of the invention, the smallest inner diameter of the electrodes is at most twice the beam diameter and the axial length of the focusing period at least 1.5 times the beam diameter.

According to a further development, the smallest inner diameter of the electrodes is not essential larger than the beam diameter, and the axial

Extension perpendicular to the coordinate χ is shown. It is assumed that the grids are alternately galvanically connected and that one half of the grids is at a low (positive) DC potential V _L and the other half at a high (positive) DC potential V _H. As long as no space charge occurs, the potential distribution between two adjacent grids is a linear function, as indicated by the dotted lines A. If the electron beam has an infinitely large transverse extent (width), its current density is uniform and the electron paths run parallel to the ^ coordinate, the space charge reduces the potential between the grids. In Fig. 1 shows curve B the actual potential profile that then results, where

Grids L and H. Because of the infinite expansion of the electron beam in the transverse direction (coordinate r), the change in potential for them is 0, that is:

= O

IO Equation (2) can be mathematically transformed as follows:

(1)

The potential distribution between two neighboring grids L and H can be determined from the following equation:

f ¹ - ¹ )

(2)

Here is | χ | the distance from the center plane of the respective grid L,

j ²

V {x) the direct potential at a distance | x |, V _L the low direct potential, V _H the high direct potential, a ² = 2.335 · HT ⁶ - ^ J the beam current density in A / m ² .

The curve according to equation (2) is shown in FIG. 2 shown.

As in Fig. 1, the potential curve in the space between the grids H and L is a mirror image of the potential curve in the space between the

I = 7.336 (1 + 2

where d is the beam diameter and S is the period length of the focusing arrangement. For an electron beam with a rectangular cross section

ΐ5 where | χ is the distance from the center plane of the respective grid L and thus between 0 and -y

is

(Fig. 1) lies (- ~ - = half the focusing period-

20 length).

The invention is based on the idea that an electron beam of finite dimensions can then be brought to a constant diameter along a larger path if the same potential profile can be achieved along this path as in the hypothetical model case according to FIG. 1 is present. It will be shown that, approximating to this ideal case, a focusing arrangement can be created which results in a potential profile which is not substantially different from the most favorable potential profile according to curve B in FIG. 1 differs.

When constructing a focusing arrangement

tion according to the invention, it is necessary at the interface between the electron beam and the Space charge-free area to create practically the same potential distribution as in the case of one in the transverse direction infinitely extended electron beam would exist. In the space charge-free area the potential must be the Laplace equation with the boundary conditions according to equations (2) and (3) fulfill. The total current / in a circular electron beam is then

-f- ■ 10 ~ ⁶ amps,

of the width w and the thickness t the total current L is given by the following equation:

/ = 9.340 (^ l + J / I4) * (l - yZL) F /

10 amps.

(7)

When the high potential V _n and the dimensions of the electron beam are constant I and the low potential V _{L is} changed, the beam current / changes. The current curve for a circular electron beam is shown in FIG. 3 shown. The equation of this curve is

F i g. 4 is a plot of the normalized perveance - = - as a function of - ^ A, where the per-

veanz P is defined as the · beam current / divided by the power of the effective beam voltage V _e

60 and P _{1n is} the maximum perveance, which then

takes the value 0.25. Therefore, for a circular

The maximum beam current I _m is obtained when occurs when V _L becomes 0.

In Fig. 5, there is shown schematically an experimental cathode ray tube constructed to test the theory on which the invention is based. The tube holds 10 ~ ⁶ amps in an elongated vacuum. (9) piston 1 an electron gun 3 on one

round electron beam
/, "= 14.67 (4th

_3- r2

and a catcher 5 at the other end. The electron beam runs in between. The jet generator 3 consists of a large, concave cathode 7, a heating element 9, and a focusing electrode 11 and 2 acceleration electrodes 13 and 15 which are so arranged and with such dc potentials are acted upon so that the electron beam emanates convergent from the large-area cathode 7 and when leaving the acceleration electrode 13, a beam-penetrated space is fulfilled. Measurements in electrolytic trough have shown that these conditions can be very largely achieved by using Electrodes of the type shown in FIG. 6 shown shape; let approach.

In Fig. 6, the electrodes 16 correspond to the electrodes am fed with a high DC potential Beginning and end of each period length according to FIG. 5. The seven interposed electrodes 17 within

has a much smaller cross-section. However, from about the 10th of each period length in FIG. 6th right front plane of the acceleration electrode 13 by a single, at low DC potential

the convergence of the electron orbits is canceled by space charge forces, so that from there on the electrons run roughly along parallel orbits.
To also after

The ring-shaped electrode 19, which has a double conical inner surface 21 with a minimum diameter in its central plane, is replaced. This minimum diameter is just as large as the diameter of the openings in the electrodes 16 and is not noticeably larger than the beam diameter d. In order to ensure the same potential in the entire beam cross-section, one consisting of thin wires is required

the passage of the electron beam through, the second acceleration electrode
Ensuring a parallel electron trajectory is an electrostatic one according to the invention
Focussing arrangement is provided, which consists of a close-meshed grid 23 in each of the plurality of electrodes provided with openings coaxially to the electron beam. The period length is roughly the ordered, periodically successive, circular ring, 7 times the beam diameter d. The ring-shaped ben-shaped electrodes 16 and 17 consists (diaphragms), electrode 19 has an axial length of about 0.8 d and all of which are very thin and all of the same design, with a maximum inner diameter at each end, the segment 14, the period length of the focusing 25 of about 1.6 d. The thickness of the electrodes 16 is indicated approximately arrangement (corresponding to the size S in 0.03 d. The resulting potential distribution

coincides almost completely with the ideal potential distribution (on the surface of the electron beam) according to the solid curve 20 in FIG. 9 together.

In some cases, the grids 23 are not used with pleasure because they always have a certain beam current component intercept and thus reduce the output

F i g. 1). The term "period length" is understood to mean that the potentials of electrodes 16 and 17 repeat themselves after they have passed through. The second acceleration electrode 15 is also the first electrode of the focusing arrangement. The electrode 15 and the electrodes 16 are connected to a high DC potential V _{11 of} a DC voltage source 18. The electrodes 17 placed in between are supplied with correspondingly graded DC potentials from the voltage source 18, the respective set center electrode being at the lowest DC potential V _L , so that a potential distribution between the high potential V ₁₁ and the low potential is restricted. If only the grids which are at low potential are removed, the current conduction is improved. If one also omits the grids, which are at high potential, both the current passage and the output power increase. For this reason it is advantageous in FIG. 6 to omit the grilles 23, even if this leads to a bad

V _L arises within each period length as it is in 40 tere approximation to the ideal focusing field F i g. 5 is given below. achieved. The F i g. 7 and 8 show two electrode

In this embodiment of the invention, structures without a grid, which are similar
the focusing electrodes 15, 16 and 17 on one
Voltage source 18 connected, which within

45

For each period length a potential distribution F (x) according to equation (4-) for a given minimum potential V _L and a given beam current density J is generated. For an electron beam with a diameter of about 65% of the diameter of the diaphragm openings in electrodes 15, 16 and 17, a total of 99% of the beam current introduced into the focusing arrangement was transmitted to the collector 5, i.e. only 1% of the beam current was intercepted by the focusing electrodes became.

According to another exemplary embodiment of the invention, the interposed electrodes 17 replaced by a single, appropriately shaped electrode within each period length. This only one Electrode that has the ideal boundary conditions on the surface on which equation (4) is based of the electron beam can be determined by means of an electrolytic trough. It there are many electrode shapes that approximate the ideal boundary conditions, and some of these electrode shapes are described below as examples.

The ideal boundary conditions require that equations (3) and (4) as a whole relate to the electron lattice, which is similar to that in FIG. 6 and still meet the ideal boundary conditions to some extent.

In Fig. 7, the inner diameter of the focusing electrodes 16 'and 19' is 1.34 times the beam diameter d, and the period length is 2.3 d. The electrode 19 ', which is at low potential, has an axial length of about 1.25d and a maximum inner diameter of about 1.74d at each end. The thickness of the electrodes 16 ', which are at high potential, is about 0.14d. The potential distribution that is achieved with this is shown by curve 22 in FIG. 9 shown.

In Fig. 8 is the inner diameter of the focusing electrodes 16 "and 19" 1.7 d and the period length 2.9 d. The electrode 19 ", which is on low Potential, has an axial length of 1.73 d and a maximum inner diameter at each end from 1.91 d. The thickness of the electrodes 16 ″, which are at high potential, is about 0.15 d. which is thus achieved is indicated by curve 24 in FIG. 9 illustrates. To the theoretical ideal boundary conditions to approximate with a gridless arrangement, the period length should be at least 1.5 d and the beam diameter be at least half of the (smallest) internal electrode diameter. In practice it is

with traveling wave tubes or klystrons it is desirable to have a large ratio of the beam diameter to the To use the (smallest) electrode inside diameter in order to achieve a high gain and a high degree of efficiency to reach. In these cases, the gridless electrode arrangements can provide the ideal potential distribution largely approximate.

It has also been investigated experimentally how the current passage using an electrode construction according to FIG. 8 (electrode 19 "with double, conical inner surface) and when using an electrode construction whose intermediate electrode has a simple circular-cylindrical inner surface, fails. With an electrode construction according to FIG The inner electrode surface area of the current passage was only 86%. The perveance P of the arrangement according to FIG. 8 was calculated to be about 4.4, while in the case of the circular cylindrical inner electrode surface the calculated perveance was only 4.1.

Fig. 10 shows an embodiment of the Invention for a klystron tube with two cavity resonators. The tube contains, from the left end considered on, an electron gun 25 which delivers an initially convergent electron beam, an input cavity 27, an elongated drift arrangement 29, an output cavity 31 and an electron beam collector 33. The beam generator 25 consists of a large, concave cathode 35, a heating element 37, a focusing electrode 39 and from the two accelerating electrodes 41 and 43. It supplies an electron beam of high current density, which enters the input resonator 27 with parallel electron paths entry. The outer edges of the electrodes of the jet generator lie between ceramic rings 45, which at the same time form part of the vacuum piston. The beam generator 25 is at the input resonator 27 attached by a further ceramic ring 47. The beam catcher 33 is analogous attached to the output resonator 31 by means of a ceramic ring 49.

The drift arrangement 29 and the passage openings for the electron beam in the input resonator 27 and output resonator 31 form a series of focusing electrodes of the type shown in FIGS. 6 to 8 type shown. As in F i g. 5 forms the second acceleration electrode 43 of the beam generator at the same time the first focusing electrode, which has a high DC potential. The focusing arrangement consists, moreover, of the annular disk-shaped electrodes 53 and, which are at high DC potential the intermediate ring-shaped electrodes 51, which are at a low DC potential. The electrodes 51 have double conical inner surfaces like electrodes 19, 19 'and 19 "in FIG. 6 to 8. The first two electrodes 51 are passed through the walls of the input resonator 27, the last two electrodes 51 are likewise arranged in the output resonator 31. The first and the last of the Electrodes 53 are arranged in the resonators 27 and 31.

Each of the electrodes 53 of the drift arrangement 29 is mechanically annular with the two adjacent ones Electrodes 51 connected in an electrically insulated manner, in each case by means of two ceramic ring disks 55, which are vacuum-tight on their inner edge to 'the outer surface of the electrode 51 and vacuum-tight on its circumference are attached to a metal cylinder 57, which in turn is galvanically vacuum-tight with the electrode 53 connected is. The metal cylinders 57 are provided with inner flanges 58.

Each of the interposed, annular electrodes 51 of the drift arrangement is provided with one at each end Annular disk 59 is provided, which extends outward to approximately the inner edge of the adjacent flange 58. the Dimensions of the elements "are chosen so that a broadband high-frequency short circuit between adjacent Focusing electrodes 51 and 53 are formed. Each of the electrodes 53 in the input and output resonators is similarly connected to a high-frequency choke, which is made of a ceramic Ring 61 and flanged disks 63 and 65 is formed and a broadband Establishes high frequency short circuit between the electrode 53 and the adjacent electrodes 51. Of the Input resonator 27 and output resonator 31 are connected to a coupling loop 66 for input and output. Provide decoupling of the high-frequency energy.

11 shows a modification in a partial representation of Fig. 10 using an electron gun providing a parallel beam will. The beam generator 67 consists of a flat cathode 69, a heating element 71 and a focusing electrode 73. The accelerating electrodes 41 and 43 of Fig. 10 and the first annular one Electrodes 51 of FIG. 10 are through in FIG. 11 replaced an annular disk-shaped electrode 77 with a conically diverging inner surface, which as serves as the only acceleration electrode of the beam generator and at the same time as the first, at a low DC potential lying electrode of the first period length of the focusing arrangement (cf. the potential curve 11, which also shows the potential distribution between the cathode 69 and the accelerating electrode 77).

FIG. 11 also shows an opposite to that 10 modified high-frequency choke for the annular disk-shaped, which is at high DC potential Electrode 53 in the input resonator 78. The high-frequency choke is here of two with large Ceramic ring disks 79 provided with openings, two flanged rings 81 and two flanged rings 83 are formed. The resonator 78 is connected to suitable radio frequency coupling means, which are not shown, provided. The remainder of the tube of Figure 11 is practically the same like the tube according to FIG. 10.

Claims (5)

Patent claims: 1. Electrostatic focusing arrangement for bundled guidance of the electron beam of a transit time tube over a longer distance by means of electrodes arranged coaxially to the electron beam, periodically successive electrodes, characterized in that the mutually identical, annular disk-shaped electrodes (diaphragms) are acted upon with such DC potentials that arranged at the distance of the focusing period , electrodes at a high DC potential (V ₁₁ ) alternate with sets of electrodes, the DC potentials of which decrease gradually towards the respective set center electrode at a low DC potential (V ₁ ) so that a potential change occurs along the beam path. 809 520/531 division results, which per focusing period at least approximates the equation V _L or there the equation Ui = 4- (ι ^ + suffices, in which | χ | the distance from the center plane of the respective set center electrode, V (x) the constant potential at the distance | χ |, a ² = 2.335 ■ 1O ~ ⁶ A ^ and J is the beam current density in A / m ² . 2. Electrostatic focusing arrangement for bundled guidance of the electron a drift tube over a greater distance by means coaxial with the electron beam is arranged, periodically successive electrodes, characterized in that arranged at a distance of the focusing period, at a high DC potential present, annular disk-shaped electrodes of the same orifice diameter (V ₁₁₎ ( Apertures) alternate with essentially more hollow cylindrical electrodes which are at a low DC potential (V ₁ ) and which, in particular with regard to their inner wall facing the electron beam, are designed so that a potential distribution results along the beam path that at least approximates the per focusing period equation or since the equation (VW) - ui = A- j ² suffices where | x | is the distance from the center plane of the respective hollow cylindrical electrode, V (x) is the constant potential at the distance | x |, a ² = 2.335 · 10 ~ ⁶ A ^ and J is the beam current density in A / m ² is. 3. Electrostatic focusing arrangement according to claim 1 or 2, characterized in that that the smallest inner diameter of the electrodes is at most twice the beam diameter and the axial length of the focusing period at least 1.5 times the beam diameter be. 4. Electrostatic focusing arrangement according to claim 3, characterized in that the smallest inner diameter of the electrodes is not significantly larger than the beam diameter and the axial length of the focusing period is about 1.7 times the beam diameter. 5. Electrostatic focusing arrangement according to claim 2, characterized in that the axial length of the more hollow cylindrical electrodes is about 0.8 times the beam diameter and the largest inside diameter at the ends of these electrodes about 1.6 times that Beam diameter and that the thickness of the annular disk-shaped electrodes is not greater than about 0.03 times the beam diameter. Considered publications:
French patent specification No. 1148 198. 1 sheet of drawings 809 520/531 3.68 © Bundesdruckerei Berlin