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Патент USA US2124270

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July 19, 1938.
'
L. F. BROADWAY
2,124,270
'CATHOD’E RAY'TUBE
Filed Nov. 5,’ 19:55
2 Sheets-Sheet 1
July 19, 1938.
L. F. BROADWAY
'
2,124,270
CATHODE RAY TUBE
Filed Nov. 5, 1955
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2,124,270
Patented July 19, 1938
UNITED STATES
PATENT ~ orrics
2,124,270
CATHODE BAY TUBE
Leonard Francis Broadway, Hillingdon, England,
assignor to Electric 8; Musical Industries Lim
ited, Hayes, England, a British company
i Application November 5, 1935,, Serial No. 48,348
In Great Britain November 8, 1934
16 Claims. (Cl. 250-275)
The present invention relates to improvements which would produce perfect focusing of a conical
beam of electrons.
in cathode ray tubes and the like.
Fig. 3 shows lines of force between several elec
A cathode ray tube is known which comprises a
sealed envelope having disposed within it, in the trodes of a known form of cathode ray tube.
Fig. 4 shows equipotential lines between the
order mentioned, an indirectly heated cathode,
electrodes arranged similarly to that of Fig. 3.
a cathode shield, an accelerating electrode (or ac
Fig. 5 shows equipotential lines in the neighbor
celerator) , a grid or modulating electrode, a first
hood of an electrode constructed in accordance
and a second anode and a screen such as a ?u
with the present invention.
crescent screen. Usually the shapes and dis
Fig. 6 shows another form of electrode con 10
10 positions of the electrodes and the potentials ap
plied to them are such that a roughly conical structed in accordance with the present invenon.
beam of electrons emitted from the cathode is
Fig. 7 shows the form of a cathode of a cathode
brought to a focus in the neighborhood of the
modulating electrode and to another focus on the ray tube constructed in accordance with the pres
ent invention,
15 screen.
Any such arrangement of electrodes which by
Figs. 8 and 9 showparts of the electrode system
virtue of the electrostatic field existing between
in a cathode ray tube constructed in accordance
the electrodes exerts a focusing action upon the
conical beam of electrons is known as an electron
20 lens and it is an object of the present invention to
with the present invention,
'
Figs. 10, l1, and 12 show further forms of elec
trodes constructed in accordance with the pres
provide an improved lens of this kind.
According to one feature of the present inven
tion there is provided an electrostatic electron
ent invention, and
Fig. 13 illustrates the application of the pres
ent invention to the formation of electron im
lens system comprising two co-operating elec
ages.
20
-
25 trodes having apertures through which an elec
tron beam to be acted upon by the lens system can
Referring to Fig. 1, in which there is shown an
optical lens I whose thickness is small com
of potential and hence a focusing ?eld between
the two electrodes, wherein the electrodes are so
30 shaped that at any point in a region within and
extending to the boundary of at least one of said
apertures the component of the electric ?eld
strength in directions perpendicular to an axis
which passes through the centres of said aper
35 tures is substantially proportional to the distance
of the said point from said‘ axis.
According to a. further feature of the present
invention there is provided an electrode, for use
in an electron lens, said electrode having an'aper
40 ture bounded by a surface or by surfaces of which
sections in planes normal to said surface or sur
faces satisfy or substantially satisfy the equa
tion V=2:|:L-y3, where V is a constant and :r and
all rays of light from a point 2 should pass
through, that is to say, come to a focus at, a
point 3 is that the refraction or bending occur 30
ring at any point within the lens should be pro
portional to the distance of that point from the
be passed and means for establishing a difference - pared with its focal length, the condition that
11 represent distances measured along suitably
45 chosen mutually perpendicular co-ordinates.
Further features of the invention will appear
from the following description and the appended
claims.
_
The invention will now be described, by way of
60
example, with reference to the accompanying dia
grammatic drawings in which:'-—
Fig. 1 shows the path of a conical beam of light
through a convex optical lens.
Fig. 2 shows the shape of equipotential curves
axis 2, 3 of the lens provided that the aperture
of the lens is small compared with its distance.
from the points 2 and 3. A similar condition
must hold in the case of an electrostatic ?eld
functioning as an electron lens, the condition in
this case being that the ?eld strength perpendic
ular to the axis of the electron‘lens at any point
within the lens must be proportional to the dis
tance of that point from the axis of the lens.
This condition holds only in the case of a thin
electrostatic lens, since if the lens is thick com
pared with its focal length, the inertia of the elec
trons passing through the lens complicates the 45
problem.
'
The shape of the electric ?eld which satisfies
the above condition will now be determined.
after which there will be described arrangements
of electrodes designed to produce such a ?eld.
Throughout the following calculation it will be
assumed that the electron beam itself has no per
turbing effect on the ?eld set up by the lens.
The theorem of Gauss states that if any closed
surface (S) is taken in an electric ?eld and if N 55
amaaro
denotes the component of electric intty at any,
point in this surface in the-direction of the out
ward normal, then
J'Nds = 413
where the integration is taken over the whole
surface and E is the total charge enclosed by the
surface.
.
the constant 0 does not a?’ect the shape of the
family 0! curves represented by the equation but
merely determines their position in relation to
the origin of coordinates, whilst the constant k '
merely alters the scale of the curves. These con
stants d, c and It may therefore be omitted with
out loss of generality and equation VIII reduces
'
From this equation it may be shown that with
10 in a surface enclosing no charge, the potential
V within the surface satis?es a di?erential equa
tion which is independent of the charges, lying
outside the region, which produce the potential.
Taking rectangular co-ordinates this may be
expressed by the equation
15
V=2a?~y+r____________ __ IX
It now V be given values 0, 1, 2 - - - - and
-i, -2, - - - - etc., the ?eld represented by
equation IX is obtained as a series of equi
potential curves, some of which are shown in
Fig. 2. These curves belong to two families of
hyperbolae and with the potential gradients in
10
15
dicated in the ?gure, represent the ideal con
I
which is kno u as Laplace’s equation.
verging lens. The corresponding ‘diverging lens
is obtained by reversing the sign of the poten
eld is to focus a conical beam of '
Since the
electrons " it must" obviously be a cylindrically
tials. In practice this would be done by revers
ing the sign of the potential on the electrode pro
etrical ?eld. Assuming the axis of sym
metry to be the :r-axis (and it will be seen
eventually that the .r-axis is the axis of the lens
25 and an axis of the electrode co-operating in pro
ducing the required ?eld) we have
to both families of hyperbolae.
enn
bs” f by’
80
20
ducing the ?eld, relative to the potentials of
adjacent electrodes.
It will be noted that one of the hyperbolae de
generates into two straight lines intersecting on
the X-axis and this pair of lines is asymptotic 25
-
If the origin be taken as the point of inter
section of the asymptotes equation IX reduces to
whence equation I becomes
V=2a:2—y2 ____________ __s X
Dav 962V
@1- 3;r=° -------------- -- H
It has been stated above that the intensity
(F) of the ?eld at any point within the lens must
35 be proportional to the distance of the point from
the axis of the lens. Assuming the axis of the
lens to coincide with the :c-axis, we have
80
since the e?ectpi' the ?rst order terms is to de
termine the position of the curve with respect to
the origin, without changing the shape of the
curve.
The angle between the asymptotes may be 35
found by considering the particular case when V
is zero.
Putting this value of V in equation X
Zea-312:0
where Fy represents the ?eld strength in direc
tion 1! and It represents a constant. Di?erentiat
ing equation III, we have
b’V
45
and
b_‘-ya = ‘—
_ _ _ - - _ _ _ . _ - - _ -
IV
and substituting for
922
by;
_
so in equation H
biV
Biz-2' '- 2k — 0 ____________ _ _
Integrating equation V
55
V
‘
V=kx2+cx+d ____________ .... VI
where c and d are constants so far as a: is con
40
and the asymptotes are given by
a+\/§r=0
e—\/§r=0
45
The angle between the two straight lines repre
sented by these equations is 70°32’ and it should
be noted that no alteration of the constants of
the ?eld equation
which has been derived
can alter this angle, it being a fundamental 50
property of any cylindrically symmetrical ?eld
of the mud under consideration.
It can be proved generally, in fact, that in any
cylindrically symmetrical ?eld of this type, the
?eld near the axis has two asymptotes which 55
intersect at the angle 70°32’.
An arrangement of electrodes which will pro
duce a ?eld of the kind shown in Fig. 2 may
cerned but may be functions of 1!,
Integrating equation m
now easily be round.
_
A known arrangement of electrodes in a cath
where e is a constant so far as y is concerned
but may be a function of z.
Combining equations VI and VII
4
V=k(2x2——y’)+cx+d
____ __.
VIII
where c and d are constants.
It can be seen by di?'erentiation that equation
VIII is a solution of equation 11 and that it
70 satis?es equation III, therefore it must represent
the ?eld required.
'
The constant it is obviously an added potential
which does not a?ect the shape of the ?eld but
merely admits of the solution being ?tted to the
35 boundary conditions of a given problem. Also
60
ode ray tube is shown in Figs. Sand 4; in both of
these ?gures it represents a cathode, 5 a. cathode
shield, '6 an accelerating electrode, 1 a grid or
modulator and 8 a ?rst anode. Throughout the
following description the cathode shield 5, cath 65
ode tl and modulator ‘i will be assumed to be at
substantially zero potential and the accelerator 6
and the ?rst anode 8 at positive potentials. In
Fig. 3 the lines of force between the various elec
trodes are shown and in Fig. 4 the equipotential 70
lines in the neighbourhood of the accelerator and
modulator are shown.
Referring to Fig. 3, an electron approaching the Y
‘accelerator and being slightly oil the axis of the
tube is accelerated by the ?eld away from the axis
I
3
amaavo
and on passing through the accelerator is again
accelerated away from the axis, so that a conical
beam of electrons whilst passing through the ac
celerator experiences a diverging effect.
At the modulator the component of the?eld
normal to the axis is opposite to that at the ac
celerator and a conical beam approaching and
passing through the modulator is converged. .
That such is the case can also be appreciated
from an inspection of Fig. 4. In the neighbour
hood of the aperture in the accelerator 8 the
potential is increasing from the axis outwards to
the accelerator so that electrons are urged of! the
ing the accelerator and has a semi-vertical anglev ,
of 54°.44', so that it forms‘an asymptote to the
equipotential curves. The cathode shield v5 sur
rounding the cathode has a diaphragm portion
20 which is shaped to form a continuation of the
surface IQ of the cathode l. With the electrodes
shaped in this manner, the ?eld between them
will be of the form deduced above. up to the sur-'
face of the electrodes. Instead of being in frusto
conical form, the cathode surface l9 and the por 10
tion 20 of the cathode shield 5 may be curved to
the shape of the equipotential surfaces of the ?eld,
for instance those marked a or b in Fig. 7. Fur
axis, whilst the reverse takes place in the neigh
ther, the accelerator 6 may have the form illus
bourhood of the modulator.
trated in Fig. 5.
'
Now near the centres of the apertures in the
accelerator and modulator the equipotential
curves approximate roughly to the ideal curves
which have been calculated above and which are
shown in Fig. 2, but near the edges of the aper
tures the equipotential curves depart widely from
-
15
Fig. 8 shows the electrode arrangement of Fig.
4 in which the curved electrodes according to the '
present invention are substituted for the dia
phragm electrodes of Fig. 4. The lines between
electrodes represent the equipotential lines in 20
the electrostatic ?elds. With the electrodes
shaped as. shown, the equipotential lines conform
to the system given by equation X above through
out the electrostatic ?eld; the asymptotes c, d and
e, ]‘ intersect in the centre of the electrode. With 25
the calculated ideal curves since the outermost
equipotential curve is represented by the section
of the surface of the electrode itself and this sec
tion clearly does not belong to either of the fami
lies of hyperbolae shown in Fig. 2. This is ob ‘ the potentials of the electrodes as stated above,
the lens between the cathode 6 and the ac
viously a serious defect in known focusing ar
celerator
B will be diverging, and the lens between
rangements especially in the case of an aperture,
. the accelerator 6 and the modulator ‘i will becon
such as the accelerator, which is ?lled with elec
with a suitable choice of the strength of 30
trons, since in this case if the paraxial region verging;
potentials on the electrodes, and their relative
of the beam is correctly focused the marginal the
dispositions, the net result of the two lenses may
region is not.
'
In order to obtain a field which is correct up
to the edge of the aperture, the electrode must be
of such shape that its surface, which is an equipo
tential surface in the ?eld, forms part of the sys
tem calculated above.
s
'
be made converging,'the conical beam of electrons
being focused at a point near the aperture of the
modulator, electrode ‘I. The beam diverging from 35
this point may be focused upon a screen as
sociated with the tube by a suitable lens system,
'
for instance by the ?eld between two tubular elec
One such electrode is shown at 9 in Fig. 5; any trodes usually termed the ?rst and second anodes,
section of this electrode in a plane containing the , the ?rst anode being held at a high positive po—'
\ tube axis Iii comprises two straight lines (neglect
tential relative to the modulator electrode, and
ing the discontinuity at the aperture) intersect
the second anode being for example held at a
ing on the axis at an angle of 70".32'. These high positive potential relative to the‘?rst anode.
lines thus form- a part of the asymptote oi‘ the These electrodes may be ‘arranged in the manner
two families of hyperbolae calculated above.
described in co-pending application No. 745,838,
The electrode can be made of two frusto-conical ?led September 28, 1934, by I. Shoenberg, et al.,
diaphragms II and I2 inserted into a tube, the entitled “Cathode ray tubes". In Fig. 8 a part of
diaphragm ll nearer the cathode having its apex the ?rst anode 8 is shown, provided with a dia
turned away from the cathode and the other i2 phragm 2|, which is placed su?lciently far in the
having its apex turned towards the cathode. The tube from the modulator 'I that it does not distort
semi-vertical angle, i. e. the angle lying between the ?eld existing ‘in its neighbourhood. Either of
the surface II and the axis 10, of each diaphragm the electrodes 6 or ‘I may have the form illus
is 54°.44'.
.
trated in Fig. 5, instead of, as shown, that illus
In Fig. 6 there is illustrated an electrode l3 trated in Fig. 6.
which is of theoretically better shape: any sec
In a preferred arrangement the ?rst and second
tion of this electrode lying in a plane containing anodes may have the form shown in Fig. 9. As
the axis l4 approximates to one curve of the ideal ' shown in this ?gure two tubular electrodes 8 and
family of hyperbolae, so that the field produced is 22 are provided with two frusto-conical portions
theoretically correct right up to the electrode. 23 and 24 arranged baseto base as shown in the
Such an electrode may be pressed out of sheet ?gure. The angle 9 between their surfaces is ar-‘
‘
ranged to be 70°32’, so that they form the
) metal.
The cathode also may be shaped to conform to asymptotes of the system of curves calculated
the system of equipotentials calculated above. In above. The ?eld between the electrodes will then
Fig. '1 is shown a cathode I heated by a heater be of the required form according to equation X,
coil l8 supplied by alternating current from the - up to the surfaces of the frusta 23 and 24. The
secondary winding ll of a transformer 40. The electrodes are preferably provided with dia~
cathode 4 is surrounded by a cathode shield 5. phragms 2| and '25, and 26 respectively, which
In front of the cathode is arranged an accelerator should be arranged sufficiently far from the
electrode 6 of the type illustrated in Fig. 6. The focusing ?elds to prevent them from distorting
cathode and the cathode shield 5 are connected '
to the centre part of the secondary winding 4|
of the transformer 40 and to the negative terminal.
l2 of the battery '43. The positive terminal 44 of
the battery 43 is connected to the accelerator
electrode 6. The emitting surface ill of the cath
ode is i’rusto-conical in‘shape, with its base fac
these ?elds.
A
In Fig. 10 is shown an alternative form of elec
trode which may be used in any of the systems
described above. The electrode is formed of a
tubular portion l8’. and carries a number of an
40
45
50
55
60
65
70
nular diaphragms 3|, the internal diameter of 75
aieasro
which decreases towards the centre of the tube
the screen in number proportional to the light
It’.
falling on that point. These electrons are then
focused by means of the field between two elec
trodes 2t and hi on to the screen 28 to form an
inverted electron image thereon. To obtaincor
rect focusing, the ?eld should have the form
The internal edges of the annular dia
phragms are so positioned that they all touch a
surface which is a surface of revolution of one
member of the system of curves shown in Fig. 2.
Thus this diaphragm is in e?ect similar to that
shown in Fig. 6 and electrodes built up, as in
given by Equation K above, and to this end the
Fig. 10, of a suitable number of diaphragms ar
ranged to simulate a thicker diaphragm having
10 continuous boundaries are regarded in this speci
?cation and in the claims as the equivalent of the
electrodes is and 35 are provided with frusto
conical portions 3d and 32 respectively, the semi
vertical angle of the frusta being‘ preferably
was. If the electrodes are then held at suit
latter diaphragms.
' able different potentials (the potential of the
In Fig. 11 is shown a form of electrode similar
to that shown in Fig. 5, but which conforms more
15 closely to the theoretical system of curves. The
dotted line 35 indicates the theoretically correct
shape of the'electrode. The electrode shown in
Fig. 11 is made of two frusto-conical portions
36 and 3'5 arranged with their smaller diameter
20 ends adjacent one another. A tubular portion
38 is arranged between the two frusto-conical
electrode as being usually more positive) the ?eld
between the screens 2‘? and 28 will cause substan
tially all electrons emitted from a point on the;
screen N to be focused on to a corresponding
point on the screen 28. Clearly if desired the
shape of the portions 80 and $2 of electrodes 29
and 88 respectively may be curved to conform
more exactly with the required form of equi El
potentials in the focusing held.
In any of the above described examples, where
electrodes in the form of conical frusta having
semi-vertical angles of 54‘244’ have been de
scribed, such electrodes may be replaced by elec
portions 36 and 3?, and ?xed to the tubular por
tion 38 is arranged an annular diaphragm 39, the
aperture boundary or inner edge of which is ar
25 ranged to lie'on the theoretical curve 35. This
form of electrode can be arranged to simulate
trodes having the form of the surface of revo
lution of one of the hyperbolae of the form given
fairly closely the theoretically correct form de
scribed with reference to Fig. 6.
An alternative structure for the electrode of
30 Fig. 11 is shown in Fig. 12. Here the tubular
portion 38 is omitted, and the diaphragm por
tion 39 is attached to the main supporting tube
IS’. The surfaces of the frusta 36 and 8? and
the inner edge of the diaphragm portion .89 all
35 lie on a surface approximating ‘to the theoretical
ly correct surface deduced above, which is shown
in dotted lines at 35.
by Equation X, and shown in Fig. 2.
the optical case of a cylindrical or other lens .
having different forcusing powers in di?erent
planes. Such electron lenses may clearly be
formed by electrodes shaped in cross section in 35
the same way as those described above (for ex
ample in Figs. 5 and 6), but having the aper
ture in the electrodes other than circular, for
Slight departures from the theoretical shapes
described above may be made in order to allow for
40 disturbing conditions such as the space charge
example in the form of a rectangle having one
side longer than the other.
A lens system 40
has properties analogous to those possessed by an
optical cylindrical lens.
The above description has been‘concerned for
the most part with electron lenses formed be 45
tween two apertured electrodes. ‘In Figures 7 and
within the tube, for example. Thus the optimum
semi-vertical angle of the diaphragms of the elec-_
formed by two or more electrodes of this nature
trode 9 shown in Fig. 5 may be either greater or
Similarly the electrode it
shown in Fig. 6 may depart from the theoretical
‘ less than 54°44’.
45 shape at the position IS in order to avoid an edge
at the join of the electrode it to the tube It in
which it is mounted. It has been found however
that the divergences from the theoretical value
need only be’slight in order to correct for dis
8 there are shown arrangements in which elec
tron lenses are formed between electron emitting
surfaces it and apertured electrodes 8. It is to
be understood that the present invention is also
applicable to electron lenses formed ‘between 50
50 turbing conditions.
The invention is not limited to the production
of electron lens systems and electron focusing
?elds for the purpose of focusing the electron
beams in cathode ray tubes of ‘the usual type
55 alone.
an apertured electrode and an electron receiving
screen, such for example as a mosaic or a duo
rescent screen. The electron receiving surface
is then shaped in the same way as the emitting
55
surface it of Figs. 7 and 8.
It is also applicable to all cases where
electron focusing is desired. For example, certain
known methods of transmitting images of‘ an ob
ject to a distance‘ include the step of projecting
an optical image of the object to be transmitted
upon a photo-electrically active screen. From
each point on the screen electrons are emitted
which are proportional in number ‘to the in
tensity of the light falling on the respective points
on the screen. These electrons are then focused
65 or directed on to a mosaic screen of mutually in
sulated elements, to form an electron image
thereon, and to charge the elements according to
the number of incident electrons. These charges
are then utilized to form picture signals for trans
70 mission. The present invention provides suitable
means for effecting this focusing.
As shown in Fig; 13, an optical image of an
object is formed by means of a lens 33. on a
semi-transparent photo-electrically active screen
75 2'5.
Electrons are emitted from each point on
'
In certain cases it may be desirable to produce
an electron focusing‘ ?eld which is other than 30
circular in shape, i. e. one which corresponds to
i I claim:
1. An electrostatic electron " lens system com
prising two co-operating electrodes of hyper
bolical cross-section, at least one. of which is
'
apertured to admit the passage of electrons, said 80
electrodes being adapted to have different po
tentials‘ applied thereto to provide a focusing
‘?eld therebetween, said electrodes being so
shaped that at any point in a region within and
extending to the boundary of the aperture in 65
said apertured electrode the component of said
focusing held in directions perpendicular to the
axis of symmetry of said aperture is substan
tially proportional to the distance of said point
70
from said axis.
‘
2. An electrostatic electron lens system com
prising two co-operating apertured electrodes of
hyper-helical cross-section, through which an
electron beam to be acted on by the Ienssystem
can he passed, said electrodes being adapted to
5
2,124,270
trode, a cross section of said apertured electrode
have different potentials applied thereto to form
a focusing ?eld therebetween, said electrodes be
being bounded by two frusto-conical portions, ar.
ranged with their smaller diameter ends adia
ing so shaped that at any point in a region with
in and extending to the boundary of at least one
cent one another, the surfaces of said frusta ap
proximating to the surfaces of revolution of a line
of said apertures, the component of said focusing
?eld in directions perpendicular to a hne which
passes through the centres of said apertures is
substantially proportional to the distance of the
said point from said axis.
satisfying the equation V=2a:*-y’, said frusta
having between them an annular portion, the
inner edge of which lies substantially on the
curve V=2:r"-y=, where V is a constant, :1:
represents distances measured from a fixed point
along the axis of said frusta, and 1! represents
distances from said axis.
12. A cathode ray'tube comprising an indirectly
heated cathode having an emitting surface, the
emitting surface of said cathode having the form 15
of a surface of revolution formed by rotating
3. An electrostatic electron lens system com
10
prising two tubular electrodes, said electrodes be
ing adapted to have different potentials‘ applied
thereto, said electrodes having surfaces facing
one another of frusta-conical shape, the angles
15 between said surfaces of said frusta and the axis
.of symmetry of the lens system beingysubstantial
' 1y equal to 55°.
about an axis a line substantially satisfying the
equation V=2:c*—y’, where V is a constant, :c
is the distance along said axis from some ?xed
'
4. An electrostatic electron.lens system com
prising two tubular electrodes and being adapted
to have different potentials applied thereto, said
point, of any plane perpendicular to said axis and 20
intersecting said line and 1! is the distance from
said axis of the intersection of said line with said
electrodes having surfaces facing one another of
frusto-conical shape, said electrodes lying wholly
without each other.
5. An electrostatic electron lens system com
'
prising two tubular electrodes and being adapted
to have different potentials applied thereto, said
electrodes having surfaces facing one another of
frusto-conical shape, the larger diameter end
of each of said frusta being arranged in reg
30 ister with one another and lying in spaced‘ par
allel planes.
6. An electron lens electrode combination com
prising an apertured electrode, the aperture in
said apertured electrode being bounded by at
35 least one surface of which sections in planes
plane.
-
13. A cathode ray tube as claimed in claim 12
and comprising in addition a .tubular cathode 25
shield surrounding the indirectly heated cath
ode, said shield having a diaphragm portion sep
arated from but forming a continuation of the
surface of said cathode.
14. Cathode ray tube comprising a ?rst screen 30
adapted to receive electrons, a second screen
adapted to emit electrons under the in?uence
of light, and surrounding the space between said
screens, means for forming on said ?rst screen
an electron image of said second screen, said 3.5
V=,2:rL-u1, where V is a constant and a: and 1/
means comprising two mutually insulated elec
trodes having frusto-conical portions, the frusto
represent distances measured along suitably
chosen mutually perpendicular co-ordinates.
base to base.
normal thereto substantially satisfy the equation
'7. An electron lens electrode combination com
conical portions of said electrodes beingarranged
-
15, Cathode ray tube comprising a ?rst screen
adapted to receive electrons, a second screen
prising an apertured electrode" the aperture in
said apertured electrode being bounded by a sur-v adapted to emit electrons under the influence of
face of revolution formed by rotating around an light, and surrounding the space between said
axis a line substantially ‘satisfying the equation screens, means for forming on said ?rst screen
V=2z¢--z/*, where V is a constant and z and 1!
are distances measured along mutually per
pendicular co-ordinates, the a: co-ordinate being
constitutedby said axis.
8. An electron lens electrode combination
comprising an apertured solid of revolution elec
trode, a cross-section of said apertured electrode
being bounded by two surfaces having the form
of conical. frusta and being placed with their
smaller diameter ends facing one another.
9. Cathode. ray tube comprising two coaxial
tubular electrodes ?aring out into frusto-conical
portions, said electrodes being placed coaxially
with the bases of the frusto-conical portions fac
ing one another.
10. An electron lens electrode combination
comprising an apertured electrode, the aperture
in said apertured electrode being bounded by a
pluralityv of annular diaphragms of such number
and spacing as to simulate substantially an ap
erture bounded by a continuous surface, of which
sections in planes normal to said surface substan
tially satisfy the equation V=2r1—il‘. where V
is a constant and a: and v represent distances
measured along suitably chosen mutually per
pendicular co-ordinatee.
10
11. An electron lens electrode combination
comprising an aperturedqsolid of revolution elec
an electron image of said second screen, said
means comprising two apertured electrodes, each
‘aperture of said apertured electrodes being
bounded by a surface of revolution formed rotat
ing around an axis a line substantially satisfying
the equation V=2z1-y=, where V is a constant 50
and a: and 1! are distances measured along mutu
ally perpendicular co-ordinates, the :r co-or
dinate being constituted by said axis.
16. Cathode ray tube comprising an electron
receiving surface, an apertured electrode through 55
the aperture of which an electron beam to be
focused on said electron receiving surface may be‘
passed, said surface and said electrode being
adapted to have different potentials applied
thereto to form a focusing ?eld therebetween, 60
both the bounding surface of said aperture and
said electron receiving surface having the form
of a surface of revolution formed by rotating
about an axis a line substantially satisfying the
equation V=2:r’—u', where V is a constant, a:
is the distance along said axis from some ?xed
point, of any plane perpendicular to said axis
and intersecting said line and y is the distance
from said axisof the intersection of said line
with said plane.
70
woman FRANCIS BROADWAY.
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