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Патент USA US2412687

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. D¢¢17,_1946.
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2,412,687
‘ Patented Dec. 17, 1946
UNITED
STATES
PATENT
OFFICE `
2,412,687
ELECTRON LENS
Otto Ernst Heinrich Klemperer, Iver, England, as
signor to Electric and Musical Industries, Ltd.,
a British corporation
Application March 31, 1944, Serial No. 528,994
In Great Britain April 8, 1942
13 Claims.
(Cl. Z50-«1.60)
l
Z
The present invention relates to electrode sys
tems for producing electron lenses such as are
of the smaller diameter electrode (A in Figure
1B) embraced by the larger diameter electrode
employed in cathode ray tubes, electron discharge l (B in Figure 1B), and the mid-surface of the
lens is defined as the surface including -the inner
valves and other electron discharge devices for
focusing electron beams and to electron discharge UI . edge or edges cf the aforesaid end of the smaller
v. devices including such systems.
diameter electrodes. Thus, in the case shown in `
An electrode system for producing an electron
Figure 1B the mid-surface of the lens is consti
lens is usually disposed symmetrically about an
tuted by the plane of the aforesaid end of the
axis and affords a passage through which the
smaller` diameter electrode, this plane being
beam to be acted on is projected. For example, 10 represented by the line M in Figure 1B. The
the electrode system may comprise two axially
electrodes A and B may be of circular, rectangualigned plane diaphragm electrodes having cen
lar, square, elliptical or other desired cross-sec
tion having axial symmetry, or they may each
tral apertures defining said passage or tubular
comprise a pair of oppositely disposed elements,
electrodes embracing said passage with their ends
or transverse edges included in planes perpen 15 for example of plate form.
In the case of an electron lens system com»
dicular to the axis, Thus, Figures 1A and 1B
prising a pair oi diaphragm electrodes the mid
of the accompanying drawing are each diagram
matic side elevational Views» of known systems of
surface of the lens is defined, as the surface mid
way Ibetween the facing surfaces of the dia
tubular electrodes, each comprising two aligned
tubular electrodes A and B respectively, through 20 phragm electrodes. Thus, in the case of the
hitherto known arrangements including plane
which the beam to be acted upon is projected.
diaphragms the mid-surface is again also a plane;
With such systems, if electrodes A and B are
In cases where the electrode system comprises
maintained at different potentials V1, V2, respec
tively, the electron lens so produced will be con
more than two electrodes the field produced is
verging whichever electrode is the more positive 25 equivalent to that of several pairs in combination,
and the system may be treated as producing a
and whether or not an electron beam is projected
from left to right or from right to left through
combination of separate lenses each constituted
the system. The focal length of the lens will
between one electrode and the next in succession
depend on the ratio of the voltages applied to the
along the axis. In the case of a system compris
electrodes A and B with respect to the cathode 30 ing three electrodes for forming a saddle ñeld
of the beam operated upon. As illustrated in
lens, the mid-surface may be deñned as the sur
Figure 1A, electrodes A and B may lbe of the same
face midway between the surfaces including the
inner edges or facing surfaces as the case may
diameter so that the edges of the electrodes are
be of the outermost electrodes, but the arrange
in registry, the electrodes being separated by a
gap G having an axial length sumcient to provide
ment can also be regarded as composed of a pair
of lenses constituted by the electrostatic fields
an adequate insulation between the two elec
trodes. In this case the electron lens is con
in the gaps between the electrodes.
stituted by the electrostatic ñeld produced about
As far as I am aware, in the prior construction
of electron lens systems employing only electrodesthe gap G and the mid~suriace of the lens,‘which
is an arbitrarily selected surface of reference 40 which afford an unobstructed >passage for the
located in the manner described, for example, in
beam to be acted upon, such as tubular or dia
the Cambridge Physical Tract “Electron opties”
phragm electrodes or combinations of tubular
by O. Klemperer, Cambridge University Press,
or diaphragm electrodes, the edges of lens-form
ing tubular electrodes in the lens i‘leld, herein
i939, is constituted by the surface midway be~
tween the surfaces including the inner edges of 45 referred to as the “inner edges,” or the facing
surfaces of the lens-forming electrodes have been
electrodes A and B, namely the edges of the elec
bounded by planes and consequently the mid
trodes A and B on either side of the gap G. As
surfaces of the lenses have been planes. I am
these surfaces are plane the midesurface is a
plane and is indicated by the chain dotted
aware, however, that electrode systems for form
straight line M of Figure 1A. If the electrodes 50 ing electron lenses have been proposed including
curved electrically conducting mesh elements
A and E are of different diameters they are pref
disposed across the path of the beam to be acted
erably disposed with the end of one electrode
inserted within theV other as electrode illustrated
on, and in some such‘constructions the mesh
inFigure 1B. In this case the lens is constituted l elements have been `so curved that `the electron
l , by the'electrostaticiield producedabout thev end, 55 lenses obtained would have curved ¿mid-surfaces.
2,412,687
4
However, electrode systems employing mesh ele
Figures 4A and 4B are plan and elevational>
ments have the disadvantages that the mesh ele
ments intercept electrons in the beam and it is
diflicult to obtain satisfactory focusing. More~
view-s respectively of an electrode system accord
ing to the invention including cylindrical elec
trodes,
over, asl far as I- am aware, the advantages to Ui
be obtained by employing lenses with curved inid
surfaces have never been appreciated.
Figure 4C is a perspective view of one of the
electrodes shown in Figures 4A and 4B,
Figure 4D is a plane development of the elec
trode ofv Figure 4C,
The ‘present invention arises out of an investi
gation for the purpose of providing improved
Figures 5A and 5B are a perspective view and
a plane development respectively of a further
electrode of cylindrical cross-section for use in a
electrode systems for producing electron lenses`
for focusing an electron beam in a, line, »for ex
ample as required in certain kinds of electron
discharge valves for high frequency operation,
system according to the invention,
Figures 6 and 7 show two electrode systems
for example, in devices of the kind known as
formed in accordance with the invention, and
Klystrons.
each of which comprises two tubular electrodes,
'
'
According to one feature of the present inven
tion an electrode system for formingan electron
lens is provided compri-sing two aligned co
operating electrodes affording an unobstructed
passage for anelectron beam to be acted upon,
and having the inner edge or edges or” each elec
trode presented to the inner edge or edges of the
other, said edge or edges being so curved that the
mid-plane of said lens is curved.
According to another feature of the present
invention an electrode system for forming an
one of which is of smaller diameter than the other
and has one end inserted within the other elec
trode in the manner described with reference to
Figure 1B above,
Figure 8 illustrates a construction of an elec
trode for use in the system in accordance with
the invention of which the 1ens-forming elements
are of diaphragm form, and
Figures 9 and 10 show two electrode systems
formed in accordance with the invention and
each including more than two lens-forming
electron len-s is provided comprising two aligned
col-operating electrodes affording an unobstructed
electrodes.
.
In Figure 2 of the drawing an electrode system
is shown which is suitable for focusing an elec
passage for an electron beam and of which one
electrode is of smaller diameter than the other 30 Jtron beam at a line perpendicular to the axis of
and'has one end inserted within the other, the
edge of said end being so curved that the mid
plane of said lens is curved.
According to a further feature of the present
invention an electrode system for forming an
the System. Such a system may be employed, for
example, for focusing a, fiat ribbon-shaped beam.
The system shown in Figure 2 comprises a pair
cf electrodes A and B aligned and having their
sides in registry and aifording a passage of uni
electron lens is provided comprising. a pair of
apertured diaphragm electrodes disposed with
form rectangular cross-section throughout their
length. The electrodes are separated by a gap G
to isolate them electrically from one another.
The electrode A has horizontal sides l and 2 and
vertical side-s 3 and li, while the electrode B has
horizontal sides 5 and E and vertical sides î and
8. The horizontal sides of the electrodes A and
` Bare represented as being wider than the vertical
their apertures aligned to afford an unobstructed
passage for Van electron' beam, said electrodes
having their facing surfaces so curved that the
mid-plane of said lens is curved.
The invention also includes electron discharge
apparatus having an electrode system as above .
set forth and means for >projecting an electron
beam through said passage and means for main
taining the electrodes of said system at such
potentials that said beam i-s acted upon in a
sides, but for some applications, the sides may
all be of the same width so that the cross-section
of the electrodes is square or the vertical` sides
may be Wider than the horizontal sides.
if the electro-des A and B are maintained at
desired manner.
Among the objects of the invention are to pro
vide an improved method of and means for focus- .«
ing an electron beam.
Another object is ’to provide an improved
method of and means for reducing aberration in
an electron lens.
`
A further object is to provide an improved i
method of and means for deriving a line image
of anelectron source.
An additional object of the invention is to pro
v »vi-de an improved electron lens having a curved
mid-plane to reduce spherical aberration.
Another object is to provide an improved
method of and means for focusing an electron
beam by employing an electron lens system in
which the component electron lenses have curved
mid-planes.
.
'
v
‘In order that the said invention may be clearly
understood and readily carried into effect the
same will now be described with reference to
`Figures 2 to i0 of the accompanying drawing, of
which
Figure 2 is a perspective View of an electrode
system according to the invention,
Figure 3 -isa perspective view of an electrode
for use in a further electrode system according
to the invention, >
>
different potentials, the electron lens produced
is analogous to twov crossed cylindrical optical
lenses, one lens corresponding in effect to the ñeld
due to the sides E, 2 and 5, S of the electrodes A
and E and serving to focus a projected electron
beam at a line in the horizontal plane through
the axis of the system, and the other lens corre
sponding in effect to the field due to the narrow
sides 3, 4 and "l, 8 of the electrodes A and B and
tending to focus the beam at a line in the vertical
plane through the aforesaid axis.
`In accordancewith the present invention, :the
inner ends of the vertical sides 3, ¿i and l, 8 of
the electrodes A and B are formed with curved
edges to constitute an electron lens having a
curved mid-surface. Thus, in the example il
lustrated in Figure 2 the curved edges are cut
to conform to cylindrical surfaces of radius R
having their axes perpendicular to the axis of
the electrode system, the curved edges on’ elec
trode A being recessed and the curved edges on
electrode B being convex and complementary to
those of electrode A. The mid-surface of the
electron lens will then be a cylindrical surface of
radius R located in the middle of the gap G.
>,Such a system is found to give better focusing
75 of a» beam of given cross-section than a system
5
42,412,687
“having au the innereedges straight ‘and win
handle satisfactorily a beam filling a greater
part of the cross `section of the electrode sys
tem. ‘ For best results, the radius R is pref
erably made small, for example, it may be made -
6
l*lens forming electrode system than it is on the
edges‘thereof. ï
» Figures 4A to 4D of the drawing illustrate the
applicationV of the invention to a system of elec
trodes in which the electrodes are cylindrical and
'half the width ofthe vertical sides of the elec
afford a passage of uniform circular cross-sec
trodes A and B so that the edges thereof are
tion throughout. This system, like the systems
Besides improving the focusing
described with reference to Figures 2 and 3 is
intended `for focusing a ribbon shaped beam to
. semicircular.
' properties of the lens, the curvature of the mid
-surface also controls to some extent the focal 10
Vlength of the lens.
If theV electrode B is maintained at a higher
_positive potential than the electrode A, a parallel
electron beam `passing through the lens field will
a line.
`
Referring to Figures 4A and 4B it will be Iseen
that the electrode system shown comprises a
pair of electrodes A” and B” having their edges
formed with diametrically opposed projecting
be caused to converge whatever the ratio of the 15 portions II, I 2 or I3, I4 as the case may be, the
edges being complementary. The electrodes A”
voltages on the electrodes. However, if, in the
arrangement of Figure 2, the electrode A is main
and B" are identical in form, the single elec
trode B" being shown in Figure 4C and a plane
tained at a more positive potential, the lens field
development of this electrode is shown in Fig
will cause a beam projected through it in either
20 ure 4D. From the latter figure it will be Iseen
direction to diverge.
that the projecting portions I3 and I4 are formed
As already pointed out, the vertical sides 3, 4
by cutting the edge of the electrode to conform
and l, 8 of the electrodes A and B of Figure 2
passing through the electrodes. 'I'hey also cause
to a series of semicircular arcs I 5, I6, I‘I and I8
each of radius equal to an eighth of the circum
the focal line obtained when a ñat, ribbon
ference'of the tube, the arcs being alternatively
shaped beam is projected through the system to
be curved especially in the vicinity of the sides.
convex and recessed.
have a slight focusing action on an electron beam
The electrodes may be
formed by severing a single flat sheet of mate
rial along the line of the arcs I5 to I8 and roll
These difficulties can be avoided by curving the
ing the two severed portions of the sheet to pro
inner edges of the horizontal sides I, 2 and 5, 6
of electrodes A and B. For example, Figure 3 30 vide the electrodes.
The system of Figures 4A and 4B will focus a
shows a perspective View of an electrode B' which
beam having a diameter equal to the radius Rr
corresponds to the electrode B of Figures 1 and
of the tubular electrodes at a line without giving
2, but which has the edges of its wide sides 5, 6
rise to any appreciable aberration and with quite
cut away or recessed to‘conforrn to a cylinder
small ratios between the voltages on the elec
of radius RI. If the electrode B’ is employed
trodes. For example, to produce a line focus at
with a co-operating electrode similar to the eleca distance of ñve `tirnes the tube radius from the
trode A of Figure 2 but having the .inner edges
principal plane of the lens system the voltage
of its horizontal sides such as I, 2 convexly curved
ratio is only about 1.4 whereas a straight edge
to conform to a cylinder of radius RI, then if the
value of RI is correctly chosen an electron lens 40 two-tube lens requires a voltage ratio of about
,
may be produced which is effectively the equiv
alent of a 'single pair of wide plate form ele
ments corresponding to the sides I, 2 and 5, 6
of electrodes A and B without the vertical sides
3, 4 and '1, B, though the vertical sides are still
present to shield the path of the beam through
the electrodes.
The radius RI may be made
quite small, for example, a simple, but quite ef
fective, construction is afforded by making the ,
edges of the horizontal sides semicircular, the
curvature of the edges of the horizontal sides
being determined by the width thereof.
In the systems described with reference to
Figures 2 and 3 of the drawing the curvature
of the mid-surface of the lens is identical with
that of the surface in which the curved inner
edges of the lens-forming electrodes A and B
, or A’ and B’ are located, but it is not essential
six to give the s_arne focal length.
However, the length of the focal line may be
greater than the original diameter of the beam
and the beam may be divergent in directions par
allel to the plane, and, in fact, with the construc
tion of electrodes described with reference to Fig
ures 4C and 4D, the divergency of the focused
beam is such that the focal line will have a length
of the order of twice the diameter of the original
beam. If it is desired that the beam shall not be
divergent, or should be of different divergency the
inner edges of electrodes A" and B" can be
shaped accordingly. For example, if, instead of
cutting the inner edges of the electrodes to con
form to semícircular arcs of radius
(or one eighth the circumference of the tube) as
that this should -be so. Thus the curvature of 60 described with reference to Figure 4D, the arcs
the inner edgesof the electrodes may be made
are not made semi-circular, but are given a radius
to diiîer so that the curvature of the mid-surface
» 21rRr approximately, a system which produces
is different from that of the edges of either elec
' practically no divergency of the beam will be pro
trode. For example, if the radii of the register~
duced. The focal length of the system will be in
ing edges of the electrodes differ by an amount 65 creased however, and also the aberration pro
equal to the width of the gap G, the radius of
duced. Such behaviour is of course to be expected
the mid-surface will be equal to the mean of
from the fact that as the radius of the arcs I5 to
the radii of the adjacent edges. Furthermore,
vI8 is increased, the electrodes A” and B” become
the inner edges of the electrodes A and B need
more nearly straight edged. Thus, if the radius
not conform-Ito cylindrical surfaces. For ex
¿is increased indefinitely a system producing a
ample, in order to correct for aperture error cor~
» «point focus would‘be obtained. From this it will
. responding to' _spherical aberration in an optical
¿be appreciated that if the radii of the aforesaid
lens, it may be- desirable to cause the radius of
- arcs are greater than 21rRT the beam will con
`curvature of the mid-surfaceto be greater at the
VergeV after passing through the lens systems
center of the lens neld about' the> axislof the.` 75 "there Ybeing two real focal lines for the lensdis
'2141256.87
- While in the Vdetailed description above, the
In some cases a satisfactory focusing of a rib-
application of the invention to lens forming sys
tems .including tubular electrodes has been- .de
scribed, the invention may also be appliedto sys
bon shaped beam may be obtained with comple
mentary cylindrical tubular electrodes formed in
the manner illustrated at A’" in Figures 5A and
tems-in which diaphragms are employed as lens
5B with straight edge portions l2l and 22 alter
nately with arcuate portions either convex as
shown at 23 and 24 in Figures 5A and 5B or con
cave.
8
_the construction of Figure 6 being particularly
valuable in this respect.
¿posed at different distances fromthemid-surface
and in planes at right angles to each other.
forming elements. For example, in Figure 8 of
the drawing an electrode D is shown constituting
of a rectangular tube 21 constituting a shield
However, a lens system formed of elec- `
portion, the shield portion having one end closed
.by a diaphragm 28, constituting the lens-forming
element, the diaphragm being curved to conform
trodes constructed in this manner is no-t- thought
to have a very wide application. It is believed
that having regard to the description already
given with regard to the system of Figures 4A
to a cylindrical surface and havingv a slot 29 eX
tending parallel to its curved edges. This elec
and 4B, the Inode of operation of a system em
ploying electrodes formed in the manner indi
cated with reference to Figures 5A and 5B will be
trode may be arranged to co-operate with a sim
ilarly formed electrode but with the end carry
ing the diaphragm recessed and curved in a man
ner complementary to the curvature of the end
of the electrode D. With such an arrangement,
if a iiat ribbon-shaped beam is projected axially
through the system with its longer dimension in
the direction parallel to the edges of the slots
such as 29 in the diaphragm, and the electrodes
are maintained at different potentials, the beam
understood without difficulty.
Figures 6 and 7 of the drawing show theappli
cation of the invention to lens systems of the
kind described above with reference to Figure 1B,
in which the lens ñeld is formed at the end of a
tubular electrode inserted within‘another elec
trode‘of larger diameter. ’Thus, in the example
shown in Figure 6, the system is constituted by
co-operating cylindrical electrodes A” and C, the
will be focused at a short line.
In'some applications, diaphragms'such as 28
might be constituted simply by elements in the
form of strips separated by a gap corresponding
above, and having this end inserted within the 30 to the slot 2:23, and the shield portion 2‘! might
electrode A" having one end formed with pro
jecting portions Il and l2 in the manner de
scribed with reference to Figures 4C and 4D
larger diameter electrode C, shown partly broken
away to show the `disposition ’of parts within its
be omitted.
Figures 9 and 10 show the electrode systems for
interior.
a conducting coating on the neckof a cathode ray
tube for example. Preferably the electrode A" .i
producing a plurality of lenses having mid-sur
faces curved in accordance with the invention.
The arrangement of Figure 7 includes three
of Figure 6 carries a conducting flange 25 for ef
electrodes 3E?, 3|, 32, separated by gaps 33, 34,
rî‘heelectrode-C may be constituted by
the two mid-surfaces of which are oppositely
fectively closing the endI of `electrode C so as to
shield the lens field from field penetration
through the gap between the electrodes. A suit
curved. The potentials V1, V2, V3, respectively,
able gap must be maintained between the flange i
25 and the electrode C for insulating purposes.
With the arrangement o-f 'Figure A6 the lens field
to increase or decrease successively, or the elec
trode 3i may be at a more positive or less posi
tive potential than either of the electrodes 30 and
obtained is similar in effect to «that produced by
the system of Figures 4A `and 4B, which has been
described in detail above.
32. If the potential of the electrode 3| is lower
of the electrodes Bü, 3l and 32 may be arranged
than both of the electrodes 3i) and 32, a saddle
u...
Si field is produced.l In Figure 8'an electrode sys
Figure 7 shows an arrangement similar to that
tem is shown comprising five electrodes 35, 36,
shown in Figure 6 but in which the cylindrical
3?, 33, 39, separated by gaps 4U, 4l, 42, 43, the
electrodes being formed with curved edges in ac
electrode A" is replaced by an electrode A’ of
cordance with the invention. In operation the
square cross-section, and the inner end of which
is formed with semi-circular edges in the manner 50 potentials V1, V2, Va, V4, V5, respectively, of these
electrodes may be arranged to increase or de
described with reference to Figure 3 above. The
crease successively to provide a series of similar
effect of the square section electrode A’ is sub
lenses.
stantially the same as that of a tubular electrode
Having now particularly described and ascer
such as A" of ÍFigure 6 of a diameter equal to the
tained the nature of my said invention and in
length of the side of the square cross-section, and i
it will be appreciated that the curvatures of the
what manner the same is to be performed, I de
clare that what I claim is:
inner ends of the electrodes A” and A’ of Figures
l. .An electrode system for forming an electron
6 and 7 can be varied 'in the manner indicated
lens comprising two aligned co-operating elec
with-.reference to Figures 4A and'4B_above, the
lens being diverging or converging or substantial 60 trodes "affording an unobstructed passage for an
ly ineifective in planes parallel vto the plane of
electron beam to be acted upon, and having the
» symmetry between the projecting portions of the
inner edges of each electrode presented to the
adjacent inner edges of the other of said elec
electrode according to the curvature of the edges
trodes, said edges being differently lcurved with
of electrode A’ or A" as the case may be.
The construction shown in Figures 6' and ’7 are
particularly free from errors due to misalignment
of the lens forming electrodes yand are eminently
Asuitable for use in cathode Yray guns. The choice
Y respect to each other to provide a curved lens
mid-plane, the curvature of said mid-plane being
related to the shape of said electrodes to mini
mize spherical aberration in said lens.
«, as to whether a cylindrical electrode such as A”
2. An electrode system of the type described in
lof Figure 6 or a square section electrode such as 170 claim l characterized in thatsaid adjacent inner
,'A’ of „Figure 7 is employed will depend on which
edges of said electrodesare -concentrically curved.
_- electrode is the more suitable for incorporation in
3. An electrode system of the type described >in
the particular device in which it is employed.
claim l characterized in that said adjacent inner
edges of said‘ electrodes are complementarily
Both constructions give lens fields with excellent
qualitiesin respect'of freedom from aberration, 75 curved and in registry.
,
.
,
2,412,687
9
4. An electrode system of the type described in
claim 1 wherein each of said electrodes comprises
a pair of parallel disposed plane elements dis
posed symmetrically on opposite sides of said pas
sage, said adjacent inner edges of each of said
pairs of said elements being curved t0 determine
said mid-plane curvature.
5. An electrode system for forming an electron
lens comprising two aligned co-operating elec
10
potentials to said electrodes, and wherein said
lens mid-plane curvature provides an electron
image forming a line transverse to the axis of
said electron beam.
10. An electrode system of the type described
in claim 5 including means for applying focusing
potentials to said electrodes, and wherein said
lens mid-plane curvature provides an electron
image forming a line transverse to the axis of said
trodes affording an unobstructed passage for an li) electron beam.
electron beam and of which one electrode is of
l1. An electrode system of the type described in
smaller diameter than the other and has one end
claim 8 including means for applying focusing
inserted within the other, the edge of said in
potentials to said electrodes, and wherein said
serted end of said smaller diameter electrode be
lens mid»plane curvature provides an electron
ing curved to provide a curved lens mid-plane,
image forming a line transverse to the axis of said
the curvature of said mid-plane being related to
electron beam.
the shape of said electrodes to minimize spherical
12. An electrode system for forming a corn
aberration in said lens.
pound electron lens system comprising a plurality
6. An electrode system of the type described in
of aligned cooperating electrodes affording an un..
claim 1 wherein said electrodes are of cylindrical obstructed passage for an electron beam to be
tubular form.
acted upon and having the inner edges of each
7. An electrode system of the type described in
electrode presented to the adjacent inner edges
claim 1 wherein said electrodes are of tubular
of another of said electrodes, said edges being
form,
differently curved with respect to each other to
8. An electrode system for forming an electron
provide a curved lens mid-plane between each
lens comprising a pair of apertured diaphragm
electrodes disposed with their apertures aligned
to afford an unobstructed passage for an electron
of said adjacent electrodes, the curvature of said
mid-plane being related to the shape of said elec
trodes to minimize spherical aberration in said
beam, said electrodes having their facing surfaces
lens.
diiîerently curved with respect to each other to -
provide a curved lens mid-plane, the curvature of
said mid-plane being related to the shape of said
electrodes to minimize spherical aberration in
said lens.
9. An electrode system of the type described in
claim 1 including means for applying focusing
i
13. An electrode system of the type described
in claim 12 including means for applying focusing
potentials to said electrodes, and wherein said
lens mid-plane curvature provides an electron
image forming a line transverse to the axis of said
electron beam.
OTTO ERNST HEINRICH KLEMPERER.
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