Note: Descriptions are shown in the official language in which they were submitted.
2~34920
CA~HODE/XEATER ASSEMBLY ~OR E~EC~RO~-BEAM
DEVICES
The invention relates to electronics, and more speci-
fically to cathode/heater assemblies of electron-beam de-
vices tCRTs).
This invention can be advantageously u3ed by the ele-
ctronics industry in ~V camera and picture tubes, oscillo-
scope CRTs, display tube3 and other electron-beam devices,
wheroin high beam current den~ity, high resolution, and
long service life have to be provided simultaneously with
short warm-up time and low power consumption.
The cathode/l~eater assembly is the mo~t important
component of a modern electron-beam devices and determines
its major performance parameters, ~uch as luminance (bright-
ne~), re~olution, service }ife, reliability, power require-
mont~, warm-up time, etc.
Modern electron-besm devices achieve high performance
characteristics by using directly heated cathode assembli-
es with high efficiency emitters based on rare-earth me-
tals or their borides (e.g., LQB6),
Known in the art is a directly heated cathode a~sembly,
used as the source of electrons (US, A, 4193013), compri~-
ing a thermionic emmiter in the form of a bar of lanthanum
h~xaboride fitted to a graphite heater. ~he heater ends are
connected to current-conducting leads mounted in a base of
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electrically insulating m~t0ria;.
This design arrangeme~t ~eatures a high (about 8W)
power required to he~t the thermionic emmiter due to Q
high dissip~tion of thermal energy by the surface o~ the
heater and the thermionic emitter. Thi~ loss o~ heat has
to be compen~ated by applying additional power, this re-
ducing the efficiency of this known in the art cathode
and heater as~embly.
Widely known in the art is the cathode/heater assemb-
ly for electron-beam devices (GB, ~, 1084035), compri~ing
a thermionic emitter mounted onto at least one heater ele-
ment fitted to current-conducting lead~ rigidly ~itted to
an in~ulating ba~e, and a repsller having a concave sur-
face facing the thermionic emitter at the side opposite
to the emitter's working ~-~r~ace and mounted coa~ially
with thi~ emitter.
The repeller facilitates returning part of the heat
dis~ipated by the suriaces o~ the emitter and heater ele-
ment. However, due to this knoNn in the art cathodeJheater
assembly using a repeller whose geometry is selected with-
out taking the dimensions of the thermionic emitter into
account, it is impossible to provide ma~imum di~sipated
he~t being returned back to the emitter.
In this known in the art design con~iguration the
repeller is not electrically insulated ~rom the thermionic
emitter-, thi~ res~}ting in unlimited electron emlssion ~rom
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the inoperatiYe part of the emitter facing the repeller.
This, in turn, lead~ to certain degree of cooling oY the
thermionic emitter, thu~ requiring application o~ addi-
tional heat.
It is an obJective o~ thi~ invention to provide a
cathode/heater assembly for electron-beam devices, featur-
ing a high per~ormance e~ficiency.
This is achieved by that i~ the cathode/heater as-
sembly for electron-beam devices, comprising a thermionic
emitter, mounted onto at least one heater element ~itted
to current-conducting leads rigidly fitted to a base of
insulating material, and a repeller positioned coa2ially
relative to the thermionic emitter and haring a concave
surface facing the inoperative side of the thermionic
emitter, according to the invention the focal length o~
the repeller's concave surface i9 at least one and a half
time~ greater than the ma~imal dimension of the thermionic
emitter in the tran~verse direction, with the repeller ri-
~idly fixed to the base so that the distance L between its
concave ~urface and the thermionic emitter is within the
limits
0.15R C L < 0.75R,
where R i~ the radius of curvature of repeller's concave
surface in the axial direction.
The cathode/heater assembly for electron-beam devices
of the invention features a high performance efficiency
due to the coniiguration of the repeller and its po~ition-
ing relative to the thermionic emitter and base. Electric
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insulation of the repeller Yrom the base facilitates gene-
rat$on of a ~pace electr~c charge at the emitter' 9 inopera-
tive ~ide and thu~ impede~ electron emission from this side
of the emitter, therefore further improvin~ the perfor-
mance efficiency of the cathode/heater a~embly of the
invention.
Other objectives and advantages of thi3 invention
wîll become apparsnt from the detailed description of a
preferred embodiment thereof and the accompanying drawi~g,
wherein the cathode/heater as~embly for electDon-beam
devices according to the invention is chown (in a longitu-
dinal sectional vien).
The cathode/heater a~sembly of the invention comprise~
thermionic emitter 1 mounted onto at lea3t one heater ele-
ment 2 (in the preferred embodiment being described - one
heater element 2), fitted by holders 3 to current-conduct-
ing lead~ 4 rigidly fitted to base 5 of an electrically
insulatine material, and repeller 6 mounted coa~ially res-
pective to thermionic emitter 1 and having a concave sur-
face facing the inoperative side of the thermionic emitter.
The concave ~urface of repeller 6 may, for e~ample,
be spherical or shaped as paraboloid of rotation, with
a focal length of at least one and a half time~ greater
than the tr~nsverse size of thermionic emitter 1. Repeller 6
is rigid~y fitted to ba~e 5 by bar 7 and positioned re-
lative to thermionic emitter 1 90, that the spacing ~ from
its concave surface and~thermionic emitter 1 is within
0.15R< L ~ 0.75R, wherc R is the radius of curvature of
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repeller's 6 concave ~urface in the axial direction.
The focal length of repeller~ 8 6 concave ~urface is
determined e~perimentally. At the selected relations bet-
ween repeller 6 focal length and the maximal dimen~ion3 r
of the thermionic emitte in the tran~ver~e direction,the
di~ipated heat arriving at repeller 6 i~ reflected by it
back to emitter 1 within the ~Glid angle contained between
emitter 1 and repeller 6, thu~ improving the a~sembly
performance e~ficiency.
The di~tance L from the concave ~urface of repeller 6
and emitter 1 i~ al~o determined experimentally, the above-
cited relation proving to en~ure maximal heat being return-
ed to emitter 1. Di~tance~ above the upper limit result
in high heat di~ipation, distances beneath the lower li-
mit prevent heat focu~ing on the inoperative ~urface of
emitter 1.
~ he cathode/heater as~embly for olectron-beam devices
of the invention function~ as follows.
A heater voltage i~ applied to current-conducting
leads 4, this cau~ing a heater current to flow through heat-
er element 2 and heating thermionic emitter 1 to its oporat-
ing temperature, at which electrons are emitted from tho
working and the inaperative surfaces thereof. ~he major
part of these eloctrons i~ focu~ed into an electron beam
in the electron-beam device utilizing this cathode/heater
a~embly. Electron~ emitted from the inoperative ~ide of
emitter 1 arrive at repeller 6 and charge it.
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203~920
A~ a re~ult, an electric ~ield i~ generated in the
space bctween emitter 1 and repeller 6 and ~ets up a ~pace
charge Qt the former, ~ith the space chargc den~ity in-
crea3ing till the virtual cathode thus produced does not
confine the major part of electrons emitt~d from the in-
operative ~ide of omitter 1 to the vicinity of emitter 1
~ur~ace, at the ~sme tim~ preventing it from emitting e?e-
ctrons with low initial velocities. Concequently heat 10~9-
e~ are reduced, due to restricted electron emi~ion from
inoperative ~urface~ of emitter 1. Experiment~ provsd
t~e temperature of emitter 1 to fall by about 50C when
the negative potential of repeller 6 i3 removed, ~uch a
reduction in temperature being of critical importance to
the performance of ~uch cathode/heater a~semblie~. There-
fore, electrically insulating repeller 6 from emittor 1
al~o improve~ the latter' 3 performance efficiency.
At the ~ame time, at optimal condition~, repeller 6
reflects heat back to emitter 1, thi~ allowing the heater
power to be reduced.
Thu~, ~electing optimal relations between the repeller
and emitter goometries, and al~o electrically in~ulating
one ~rom the other allow~ the proper operating temperature
of the emitter to be provided at lower heater power, thus
improving the performance efficiency o~ the cathode/heat-
er assemb~y of the invontion.
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