DE2339340C2 - Electron tube - Google Patents

Description

6> _m = Q _e + 2 πη
is satisfied, the magnetic dwell angle being through

Q _m = ci) T _L , with u> as cyclotron frequency (a> = I ₁ - B ₀ , n = ratio of charge to mass for the electron) and T _L as transit time for crossing the electrical field generating device (48) {T _L = L / Zq, L = length of the device, Z ₀ = V2 η Va, V ₀ = acceleration voltage)

is defined and the electrical angle of rotation Q _{c represents} the total angle of rotation of the field that is present between the input and output of the generating devices for the electric field, while η is a positive or negative integer (except 0).

2. Electron tubes according to claim 1, characterized in that n = ± 1 and 0 << 9 ,. S 2 π holds.

3. Electron tubes according to claim 1 or 2, characterized in that

0 <Θ _ρ <- ^ -; ϊ

4. Electron tubes according to one of claims 1 to 3, wherein the means for generating the electrical Field represents a so-called deflectron, characterized in that at the entrance of the deflectron (48) a screen (46) which is at a fixed potential and has a passage opening (47) is provided is.

5. Electron tubes according to claim 4, characterized in that between anode and screen (46) a essentially field-free running space (22) is provided.

6. Electron tubes according to one of claims 1 to 5, characterized by application to microdot tubes high beam intensity, vidicon or image orthicon tubes and X-ray tubes.

7. Electron tubes according to one of claims 1 to 5, characterized by application to monochrome or color television projection systems.

8. Electron tubes according to one of claims 1 to 5, characterized by use in high-performance tubes with focused beam for electronic surface processing, for electronic Welding or contour drilling.

The invention relates to an electron tube, in the bulb of which there is a cathode for emitting an electron beam, at a distance from the cathode an anode with a beam-limiting opening for the passage of the electron beam and at a distance from the anode, a target electrode, wherein along the bulb between the target electrode and a device for generating an electric field E is arranged on the cathode, the field direction of which is essentially perpendicular to the longitudinal axis of the bulb and rotates along the longitudinal axis by an angle which is essentially proportional to the longitudinal axis coordinate Z with respect to a fixed transverse to the longitudinal axis lying coordinate Y , so as to exert an electric force on the electron beam, the electric field at any point in time having a substantially uniform strength within the piston part containing the electric field, further including one along the piston including the electric field e device for generating a magnetic field B is arranged

the beginning of which has a certain distance from a plane containing the beam-limiting opening and which has a substantially uniform predetermined strength B ₀ along the longitudinal axis Z in order to generate a magnetic force acting on the electrons and cooperating with the electric force and cause a resultant helical movement of the electron beam.

Such an electron tube is already known from US Pat. No. 3,319,110.

The deflection systems for electron tubes of the type mentioned above, such as those for vidikons and Scanning transducers are used, must have a small shadow error, a good deflection sensitivity, a have high resolution, low power requirements and the smallest possible dimensions. The electron tube of the type mentioned with a deflection system, as is known from US-PS 33 19 110, results in good resolution, decent deflection sensitivity, and relatively low indeed Power requirement with small dimensions. The state of the art represents a "non-twisted", shadow-free one Deflection system. In this mode of operation, which guarantees freedom from shadows, however, the deflection sensitivity, the power consumption of the magnet coil and also the focal point reduction that can be achieved by focusing, which is desirable for a sufficient resolution, not yet optimal. Because it is possible to increase the deflection sensitivity by reducing the magnetic field strength and at the same time to increase the To reduce the power consumption of the solenoid. The strong prior art pre-focus lens can then omitted due to the resulting reduction in focus. However, there is now one significant shadow flaw.

The cylindrical "deflectron" required for the shadow-free operating mode of the Tecfmik booth can be replaced by a conical »deflector«, which increases the deflection sensitivity, but then the shadow flaw grows even further.

One could modify the deflector even further by "twisting" it, for example via perform an angle of 90 ° twisted. In this context, reference is made to US Pat. No. 3,666,985. This construction increases the deflection sensitivity, but worsens the shadow defect even further.

The object of the present invention is to design an electron tube of the type mentioned at the outset in such a way that that in the case of an essentially negligible shadow error, the deflection sensitivity improves, the resolution is increased and the power consumption of the solenoid is reduced.

This object is achieved in that the device for generating the is dependent on the Z coordinate rotating field and the device for generating the uniform lying in the Z-direction magnetic field are coordinated so that the equation

6>, " = Θ ,. + 2πη
is satisfied, the magnetic dwell angle being through

6>", = o) T, _, with ω as the cyclotron frequency (<y = ι, ■ B ₀ ,,, = ratio of charge to mass for the electron) and 7) as the transit time for crossing the electrical field generating device (T _L = LZZ ₀ , L = length of the device, Z ₀ = V2>, Va , V _a = acceleration voltage)

is defined and the electrical angle of rotation Q _{e represents} the total angle of rotation of the field that is present between the input and output of the generating devices for the electric field, while η is a positive or negative integer (except 0).

By these measures, both the deflection sensitivity and the resolution are improved and in addition, the coil excitation power is reduced.

For the deflection sensitivity, see equation 14 of the description and FIG. 11, that for

// = -1 the value of the deflection sensitivity K in the range of O <0 _P <2 π is always greater than \ = 0.318, that is

Value, which in the state of the art is for Q ₁ . = 0 results. The present invention provides a possible deflection sensitivity of up to 0.405 compared to 0.318 in the prior art, ie in the shadowless, non-rotated deflection system.

Minsichtlich the resolution is to say that the electron-optical magnification M according to the present invention, see the equation 18 and FIG. 14 where the magnification M is plotted as a function of _Θ Ρ, door the range 0 <0 _e <2 / rjeweils is less than 1. Since the value of M in the non-rotated shadowless system according to the prior art, in which Θ ₍ = 0, is 1, the present invention provides a smaller image of the beam-limiting opening 44 on the screen in each case (provided a magnifying pre-rocussing lens is not used.) This smaller point results in a correspondingly higher resolution when scanning.

For the coil excitation power, it must be taken into account that the required current for a given coil is proportional to the desired level of the magnetic field strength, | ß _o |, and thus also proportional to | 0 _m |. The power consumed is proportional to the square of the current and thus to the square of 0 ",. Equation 12 results in door η = -1, see Fig. 4, that for the rotated shadowless operating modes 0 < Q _e < 2 π the size of Θ ,,, <2 π is. Since in the prior art, the non-rotated shadow-free system, Q _e = 0 and thus \ Θ ,,, \ = 2 π , this means that the prior art requires a higher power for the coil excitation than the system according to the invention. ^%

It thus shows that the special coordination of the individual values according to the characteristic Part of the main claim not only a shadow error of essentially 0 is achieved, but also the Deflection sensitivity is improved, the resolution is increased and the magnet coil is less Owns power consumption.

This applies in particular if, according to claim 2, the relationship η = ± 1 and 0 < Θ ,. S 2 η applies.

The invention is explained in more detail below with the aid of exemplary embodiments which are shown in the drawings are shown.

It shows

1 shows, in a simplified representation, a schematic representation of a particular embodiment of the invention Electron tube in a longitudinal sectional view;

Fig. 2 is a longitudinal sectional view of FIG. 1 for an even more precise presentation of certain essential inventory '

3 shows a conventional "deflector" developed in one plane; ι

FIG. 4 shows the deflector according to FIG. 3 developed in one plane, but modified; FIG.
F i g. 5 is a perspective view of the modified pattern of FIG. 4 in its arrangement on the inner surface of a cylindrical body;

6a shows the coordinate system used to analyze the mode of operation of the invention and the spatial Assignments of the electric and magnetic fields of a conventional deflector;

6b shows the spatial assignments of the electric and magnetic fields in a modified form:,

Deflector; and !:

Figures 7-16 are diagrams illustrating the characteristics of the invention. :

The theory of the mode of operation of the invention is explained below with reference to the schematic "■ -"

Longitudinal section of the cathode ray tube EBT of FIG . 1, which has a cylindrical piston 20, in "ij

which a vacuum is maintained. Inside the piston 20 is an electron gun ΐ '

or an electron source 21 arranged which generates a longitudinal electron beam with a narrow opening ■ ';

angle generated. The electron source 21 is followed by a running space 22 of length A , which is in ',

be kept essentially free of electrical and magnetic fields, but alternatively also an electro-;

static prefocusing lens 23 may contain. At the distance A from the electron source 21, a cavity 24 with the length L is provided, which has a device for generating an electric field within the cavity i;

Raums 24 with essentially constant amplitude, but spatially variable orientation contains, such as which is explained in more detail below. The cavity 24 is surrounded by a magnetic coil 25 which is coaxial to the cavity 24 and extends for substantially the same distance as this. The solenoid 25 creates a substantially uniform magnetic field along the longitudinal axis of the piston 20 within of the cavity 24 is aligned. On the opposite side of cavity 24 is a target electrode 26 provided, the nature of which depends on the desired application and either so brought close as practically feasible to the end of the cavity 24 or at an optimal distance of which can be arranged.

F i g. 2 is a longitudinal section through the electron beam tube EBT of FIG . 1, the essential components of which ι

reveals. According to FIG. 2, the electron source 21 has a thermionic cathode 40, a grid 41, '

for controlling the electron flow, an anode cap 42 for accelerating the electrons and a Beam limiting electrode 43 with a small beam limiting opening 44, the opening 44 in is centered with respect to the longitudinal axis of the cathode ray tube substantially, so the radial extension limit the electron beam. The running space 22 contains a cylindrical jacket 45, which on his one end through the beam limiting electrode 43 and at its other end through a deflecting screen 46 is limited. The deflecting screen 46 is formed by a plate extending perpendicular to the longitudinal axis and has a circular opening 47 centered with respect to the longitudinal axis. The cavity 24 contains an electric field generating device in the form of a cylindrical electrostatic deflection yoke or Deflectrons 48 to generate an electric field, the properties of which will be explained in more detail below. The deflector 48 corresponds to the type referred to here as the "twist" type and has a plurality interlocking horizontal and vertical deflection electrodes. Deflectron 48 may be useful on the inner surface of the piston 20 according to conventional photographic processes, but also in any other suitable manner. The solenoid 25 is arranged so that its the electron source 21 associated end and the end of the deflector also facing the electron source 21 48 are located essentially at the same height of the longitudinal axis. The target electrode 26 is of a fine-meshed electrode 49 is formed, which has a small distance from another target electrode 50. the Target electrode 50 may be a photosensitive target electrode, a silicon oxide storage target electrode or some other suitable target structure to give the desired function. The fine-meshed one Electrode 49 is preferably positioned as close to deflector 48 as possible.

During operation, electrons emitted by the cathode 40 are accelerated and, under the action of the grid 41, the anode cap 42 and the beam-limiting opening 44, are formed into a narrow, longitudinally directed beam which passes through the jacket 45 and the deflecting screen 46 and then enters the cavity 24 to enter, where it is deflected under the action of the magnetic coil 25 and the deflector 48 and focused by the grid 49 onto the target electrode 50, from which a signal can then be read electrically in accordance with conventional reading methods. The anode cap 42, the beam limiting electrode 43, the deflecting screen 46 and the grid electrode 49 are operated with essentially the same voltage V n. Sense voltages are applied to the x and> electrodes of deflector 48 in a conventional manner. The average voltage of the scan voltage should be essentially the same as for V _B. When the voltage applied to the jacket 45 is V ₁₁ , the jacket 45 acts as a field-free running space, while otherwise it acts as a prefocusing lens. A suitable current is passed through the solenoid 25. The potential applied to the target electrode 50 depends on the nature of the target electrode, but is typically about 10 V · V ₀ can also have different values, but its value is typically about 300 V.

The "twisted" deflector 48 is created by changing the electrode pattern of a conventional deflector generated in the following manner. Fig. 3 shows a conventional deflectron pattern developed in a plane. The arrow points in the direction of the deflectron axis. The zigzag ends of the

the gripping zones 51,52, which form the χ and deflection electrodes, running line aa forms a reference line parallel to the deflector axis. Fi g. 4 shows the same pattern after a "twist". The line aa has become the line a'-a ' , which, although still straight, is inclined in relation to the axis of the deflector 48. The change is caused by shifting each point of the pattern in the circumferential direction in a direction perpendicular to the deflector axis by a distance which is directly proportional to the distance of this point in the longitudinal direction from the end of the deflector facing the electron source. When the pattern of Fig. 4 is wound into a cylinder corresponding to Fig. 5, the line a'-a ' on the surface of the cylinder describes a spiral and points at the end of deflector 48 adjacent the target electrode are opposite corresponding points at the opposite end of the deflector has been rotated by an angle Θ _Ρ , the angle 0 _{f being defined} as the electrical rotation angle. Points in between are rotated by an angle which is equal to (ZZL) Q _c , where Z is the longitudinal distance of the respective point from the end of the deflector adjacent to the electron source. A similar result would be obtained if the two ends of a conventional deflector according to FIG. 3 would be detected after rolling into a cylinder and rotated in opposite directions.

Currently known twisted deflectors have a twist determined by Q _e - π / 2 rad or 90 °. However, other angles are also possible.

It should now be shown that when the magnetic field is set to the correct value, as determined by the measure the twist is given, a hitherto unexpected new work opportunity can be obtained. To this Realize the equations for the motions of electrons in the superimposed electric and magnetic fields in the cavity 24 of FIG. 1 or 2 derived and solved. It must the condition that the shadow error is zero must be satisfied, and this condition becomes a constraint derived with regard to permissible values of the magnetic field strength.

First of all, it is necessary to set up a coordinate system. The starting point of the coordinates is in FIG. 6a and 6b on the axis at the point where the electron beam enters the deflector. The axis of the tubular envelope coincides with the Z-axis, with the unit vector ζ directed towards the target electrode. Overall, the unit vectors x, y and ζ form the basis of the right-handed, orthogonal coordinate system.

The electric field of a conventional cylindrical deflector has the value E. = 0, since the electric vector E is perpendicular to the Z-axis. The size of E and its alignment in the x-y plane are controlled in a known manner by applying suitable voltages to the deflector. Without losing sight of the general considerations, assume that E _x = 0 and E _y = -E ₀ , where E _{0 is} the length of the electrical vector E. Thus, E lies along the negative j ^ axis and generates an electrical force -eE in the positive ^ direction. Since the deflector is not twisted, the electric field has the same size and direction everywhere. F i g. Figure 6a illustrates the nature of the electrical vector in a conventional deflector. The volume of the deflector is divided by planes with longitudinal intervals of AZ = L / 4 , and the jc-v orientation of E is indicated in each plane.

The electric field of a twisted deflector can be demonstrated to be essentially perpendicular to the Z-axis. However, the orientation of the electrical vector E does not remain fixed from one end of the deflector to the other end. Rather, the vector E experiences a rotation by the electrical angle of rotation 0 _e , namely by an amount that increases uniformly with an axial distance from the starting point. The x and y components of the electric field are given by

E _x = E ₀ sin (0, ZZL) (I)

E ₁ . = -E ₀ cos (.0, .ZZL) (2)

E; = 0 (3)

Equation (3) is not entirely accurate. However, if the condition Θ, .R ₀ IL < 1 is satisfied, where A _{0 is} the maximum deflection of the electron beam, then the interfering effects of E. are small. Here it is assumed - without losing sight of the general viewpoints - that the initial direction of the e'.ektri- so see vector is along the negative .v-axis, in order to match the conventional case corresponding to FIG. 6a to match. The "twisted" situation is shown in FIG. 6b. In both FIGS. 6a and 6b the magnetic field is aligned along the z-axis so that B _x = B _y = 0 and B- = B ₀ , where B ₀ can be either positive or negative. The equations of motion can be written as follows

X = - <y Ya sin (Q ₀ ZZL) (4)

>'= + <oX + a cos (Q _e ZZL) (5)

Z = O, (6)

where the cyclotron frequency ω = > _t B ₀ and the electrical acceleration a = I ₁ E ₀ . The ratio of charge to mass for the electron is I ₁ . For equation (6) it is believed that this applies exactly, and expresses that the z-component of the velocity Z does not change, and its initial value Z ₁₁ = V2 I ₁ V _a is, ig as with F. 6a and 6b shown. It is also assumed that the electron enters the deflector without x or ^ speed, so that X ₀ = Y ₀ = 0. Since Z = Z ₀ , is the axial position

Z = Z "T f"

where T is the time that has passed after the electron entered the deflector at Z = 0.

The time is expediently measured in units of the transit time 7 ^ for crossing the deflector according to T _L = LzZ ₀ and the distance in units of R = αΤ / (2π) ² . This gives the dimensionless standardized variables χ = X / R, y = Y / R, ζ = Z / R and t = T / T _L. Furthermore, according to Schlesinger's teaching, the magnetic dwell angle 0 _{m is defined} as 0 _m = <oT _L.

With these definitions, equations (4) and (5)

x = -Θ _η y - (2π) ² sin (e _e t) (4a)

y = +0 _m x + (2π) ² cos (0 _e t) (5a)

The solutions of (4a) and (5a) for χ, y, χ and y as functions of time can be written as follows

Jrfrt- (2jt) ² Γ ^{Un & mt} - ^{Sitl0f /} Ί (8)

^{() {]} L0 _m (6> _m -6>,) 0 _f (0 _m -0,) J ⁽⁸⁾

ΙθΑΘη, -Θ ,.) 0 _m (0 _m -0 _e ) 0 _m 0 "J

«■> - * ■> ■ [Ä- S]

I e ι η Λ.1 / et η M * I

It is now necessary that the shadow error be zero. Therefore, at the exit of the deflector, where / = 1, the x and y velocity components must vanish so that the electron hits the target electrode at right angles thereto. Applying this condition to equations (10) and (11), the following result is obtained for t = 1:

0 _m = 0. ± 2nn (12)

where η is any positive or negative integer other than zero. Equation (12), which can be referred to as the zero-shadow condition, states that the magnetic dwell angle must be restricted to values that only deviate from the electrical twist angle by whole multiples of 2π radians if a zero-shadow Error should be achieved. Since 0 _m is proportional to the magnetic field, equation (12) means that only certain magnetic field values are permissible. It can be shown that if 0,. 2 exceeds π or | n | becomes large, the deflection sensitivity becomes small. Therefore, the further investigation should be limited to cases for which 0 < 0 _e <2 π and η = ± 1, since the other possibilities are fundamentally to be regarded as unrealistic or at least offer no advantages. Likewise, the various zero-shadow modes should be denoted by the applicable values 0 _e and η , since equation (12) fully defines 0 _m if 0 _e and π are given. For example, the mode (operating mode) [π / 2, -1] has an electrical twist of π / 2 rad and a magnetic dwell angle of -7> π / 2 rad. The negative sign indicates that the magnetic field is aligned along the negative z-axis. The value of 0 _r is always positive so that it has the conventional counterclockwise polarity. The mode [π / 2, +1] has the same electrical twist angle π / 2, but the magnetic dwell angle + 5π / 2, which indicates that the corresponding magnetic field has positive z-polarity. This illustrates a general result: for every value of 0 _e , mu \ n \ = 1, there are two values for 0 _m , which lead to zero shadows and therefore to two values of the magnetic field. F i g. 7 illustrative

K _n M AIn X «* rln« * _n »..« »i £ k; * t \ {ΐί- _ _1_ 1

u \ »ui un- n.-iuCiUltg vuil C7 _m , mil CT _e IUl It - _! _ 1.

If a normalized speed ν in the jr- / y-plane with

\ 55 ν = V _x ² + y ² / (2n) ²

is defined, where (2π) ^{2 is} the velocity at / = 1 for a deflector with 0 _e = 6 _m = 0, equations (10) and (11) lead to the result

1 π η

sin π nt

(13)

what in Fig. 8 for | n | = 1 is plotted. This illustrates the way in which the speed in the x - /)> plane drops to zero at t = 1, so that normal impact on the target electrode is guaranteed. 8 applies to all values of 0 _C for η = ± 1.

The projections of the electron trajectories on the x / y plane are shown with FIGS. 9 and 10 for 0 _r = 0, π / 2, π, 3jt / 2, 2π . Fig. 9 shows trajectories for η = -1, while Fig. 10 shows the trajectories for η = +1.

To compare the deflectron sensitivities that can be obtained for the various modes of the invention, such as the deflection sensitivity k as the ratio of the deflection for the mode in question to the deflection for an untwisted deflector of the same diameter and length, which without a magnetic field is operated. Using equations (8) and (9) - taking into account equation (12) - it can be shown that k is in the form

4 sin (0 _f / 2) 0 _P (0 «, + 2 π η)

(14)

can be expressed. That is, the values for Θ _Ρ and η are sufficient to determine k. Equation (14) is shown in FIG. 11 for «= ± worn. From Fig. 11 it follows that in general the highest values for k can be achieved for η = -1. The highest possible value of k occurs at 0 _e = π , where k = AIn ¹ .

The Schlesinger shadow-free mode appears here as the two special cases for O _e = 0: [0, +1] and [0, -I]. The deflection sensitivity of both modes is Μπ. Therefore, all modes of the invention result in a deflection sensitivity for η = -1 which is greater than or equal to the Schlesinger shadow-free mode, which in the present study corresponds practically to two modes.

If the scanning rotation _{angle 0 r is defined} as the angle between the positive y-axis and the ultimately deflected direction in the jr / j> plane, where Θ _{Γ is} counted positively in the counterclockwise direction, then tan Q _r = -x / y. If use is made again of equations (8) and (9) - taking into account equation (12) - the result \ n \ = 1 is:

Q _r = (0, / 2) + (π / 2), η = +1 (15a)

Θ ,. = (Θ, / 2) - (π / 2), η = -1 (15b)

Equations (15a) and (15b) are plotted in FIG. For 6 _e = π and η = -1, Q _r = 0, which indicates that no scan rotation is occurring. This can also be seen from FIG.

Figures 7 through 12 and their corresponding equations describe the operation of the electron beam deflector the invention. When considering the electron beam focusing device according to the invention it becomes apparent that the two are closely related.

It is generally known to those skilled in the art that the running space 22 of length A (see FIG. 1) and the cavity 24 of length L, which contains a substantially uniform, axially aligned magnetic field, together form an electron lens. As noted above, additional separation can be added between the deflector and the target device. That is within the scope of the invention. However, this reduces the resolution, since the achievable miniaturization of the electron lens is reduced.

As with F i g. 2, a practical embodiment of the lens has the anode cap 42 with the beam-limiting opening 44, the jacket 45, the deflecting screen 46 and the magnetic coil 25. The magnet coil should have a length which is essentially the same as the length L of the deflector. Likewise, the jacket should be operated with the anode potential, so that the running space 22 is a field-free running space.

On the basis of general theory it can be deduced that this lens forms an image of the opening 44 on the target electrode 50 when the magnetic dwell angle is 6 _m , the distance A and the length L are in relation to one another

(A / L) = -tan (6Jl) I (QJl) (16)

stand. If one takes into account the restriction for <t> _m according to equation (12), one obtains as a result

A (Q,., N) lL = -tan (6 _r / 2) l (- ^ + πn) (17)

Once the values for Q _c and η have been established, the permissible value for A / L is therefore strictly defined. F i g. 13 is a graph of equation (17) for η = ± 1. The magnification of the lens is known as

M = | cos (0 ", / 2) | (18)

Using equation (12), one obtains

M = | cos (0,. / 2) | (19)

The equation (19) is plotted in FIG. The result is independent of the value for n. The calculated value for M falls for Q ₁ . = π down to zero. In practice, M = 0 cannot be achieved because space charge effects and lens aberration phenomena that are not taken into account here limit the minimum beam size at the level of the target electrode, as does the influence of the auxiliary lens required. However, a considerable reduction can be achieved because the condition M - <1 holds everywhere.

Since the distance A can be infinite or negative, as can be seen from FIG. 13 and equation (17), it is sometimes necessary to use the auxiliary electrostatic prefocusing lens (23) of FIG. 1 to make use of. In the practical embodiment of FIG. 2, the lens jacket (25) would be operated here with a voltage different from the anode voltage V _a.

A negative value for A / L indicates that the apparent electron source must be on the target side of the entrance end of the deflector rather than on the electron beam source side. An infinite value for A / L also indicates that the electron beam must be collimated before the beam enters the solenoid. These conditions can be satisfied by operating the pre-focus lens to give a virtual electron source at the correct spacing. The resulting magnification partly depends on the focal length and the position of the pre-focusing lens.

In general, Q _{e is} preferably restricted to the range 0 < Q _e <- to avoid excessive twisting

and to avoid the complications of a strong electrostatic lens, in this range A / L is less than about 1.23 when η = -1. As a result, the maximum total length from the beam opening to the target electrode is limited to approximately twice the length L of the deflector, without the use of a strong auxiliary prefocusing lens. However, the lens-coat-Potentia! be variable in order to be able to provide for a fine adjustment of the focal point without changing the set magnetic field.

For special purposes, larger values for Θ may be desirable. For example, as indicated above, there is no rotation of the image for the mode [π, -1]. This result is achieved without the use of the multiple winding solenoid, which is required for the same purpose according to the teaching of US Pat. No. 3,319,110 - Schlesinger. The deflection sensitivity in this mode is the highest possible according to the invention.

Furthermore, for the mode [2π, -IJ without the use of a magnetic field, zero shadow is obtained because 6 _m = 0 in this case. This mode represents an electrostatic analogue to the zero-shadow mode according to Schlesinger, which is the special case [0, ± 1] or the zero-twist mode. The modes [2 / r, -1] and [0, ± 1] have the same deflection sensitivity. Mode [2n, -1] requires an electrostatic lens for focusing.

In any case, it is generally desirable to use the modes with η = -1 instead of »= +1, since the former have a higher deflection sensitivity than the latter.

It is essential to practice the invention with the correct value of the magnetic field, as given by equation (12), when the highest performance is required. An incorrect magnetic field leads to a shadow defect. If β is the angle for normal impact on the target electrode, then the shadow factor s can be defined by

tan β = s [- ^] (20)

where R _{1 is} the distance of the beam from the axis at the target electrode, measured in unnormalized units. It can be shown that

(21)

where the right side is evaluated for t = 1. The quantity s is linked to the angle of incidence and is therefore a measure of the shadow error.

F i g. 15 shows s as a function of Q _m for the case [π / 2, -I]. The correct value of Q _m is - - at which

Value s disappears. However, s increases rapidly as Q _n i differs from - -. For example, it has been shown in practice for the case [π / 2, -1] that a change of about 0.3% in the solenoid current and therefore of Q _n results in a detectable increase in the amount of shadow formation. From Fig. 15 or equation (21) it can be deduced that this corresponds to a change in the shadow factor of more than 0.014. In implementing the invention, it is therefore essential that the magnetic field is set to the correct value if the best possible shadow behavior is to be achieved.

It can be shown that the use of a conical instead of a cylindrical deflector increases the shadow factor. The conical deflector creates an electric field, the size of which varies from one end of the deflector to the other. Fig. 16 shows the relationship between the shadow factor s and the taper ratio m, that is, the ratio between the large diameter and the small diameter of the conical deflector. For m = 1 the deflector is therefore a cylinder. Curves are shown for different values of the electrical angle of rotation Q _e for η = -1. For the case [/ 7/2, -1] we can see from Fig. 16 derive that an increase from m = 1 to about m = 1.02 increases the value j from 0 to 0.014, which is known as a detectable deterioration in the shadow behavior. It is therefore essential in practicing the invention to provide an electric field device capable of generating an electric field of substantially constant magnitude in the deflector.

The curves of FIG. 16 were obtained by numerically integrating the equations of motion in the conical Deflection and focus system calculated using a computer because no exact solution is known for the conical cases.

Thus, by combining the deflection and focusing system with an extension of the rotated by 90 ° Deflectrons to any twist angle and modified by operating the resulting If the value falls below a number of precisely defined magnetic field values, the system creates a series of new shadow-free ones Modes of the system receive, for which at the same time a higher deflection sensitivity, a better resolution and a lower magnet coil power requirement than in the previously known shadow-free modes 5 can be obtained.

The system of the invention can be used in many cathode ray arrangements and for a number of applications insert. For example, the system according to the invention can be used in microdot tubes with a higher beam intensity, in monochrome or color television projection systems, vidicon or image orthicon tubes, x-ray tubes or high-performance tubes with a focused beam for electronic surface processing tion, for welding or contour drilling.

Various designs can be used for the electrostatic lens. The length of the solenoid can extend beyond the target electrode in order to reduce the peripheral fields of the magnetic coil. That Deflector can be made slightly tapered to allow easier machining on mandrels. Of the Value of 0. can be assumed negative, so that the positive and negative values of η against each other 15 be replaced. Furthermore, the solenoid may deviate slightly from the correct value Electricity operated.

In addition 8 sheets of drawings

20th

Claims (1)

Patent claims: 1. Electron tube in whose bulb there is a cathode for emitting an electron beam, at a distance from the cathode an anode with a beam-limiting opening for the passage of the electron beam as well as at a distance from the anode a target electrode, whereby along the bulb between the target electrode and the Anode means a device for generating an electric field E is arranged, the field direction of which is essentially perpendicular to the longitudinal axis of the bulb and rotates along the longitudinal axis by an angle which is essentially proportional to the longitudinal axis coordinate Z with respect to a fixed coordinate Y lying transverse to the longitudinal axis so as to exert an electric force on the electron beam, the electric field having a substantially uniform strength at all times within the piston portion containing the electric field, further means for generating along the piston an electric field confining means g of a magnetic field B is arranged, the beginning of which has a certain distance from a plane containing the beam-limiting opening and which has a substantially uniform predetermined strength B ₀ along the longitudinal axis Z in order to act on the electrons with the electrical force to generate acting magnetic force and to cause a resulting spiral movement of the electron beam, characterized in that the device (48) for generating the field rotating as a function of the Z coordinate and the device (25) for generating the in the Z direction lying uniform magnetic field are coordinated so that the equation