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Oct. 22, .1946'.v
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c.-M. sLAcK ETAL y
2,409,717
FIELD EMISSION ARC DISCHARGE TUBE
‘ Filed sept. 2s, 194;'v
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INVENTORS
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ATTORNEY
Patented Oct. 22, 1946
2,409,717
NUNITED STATES PATENT OFFICE
2,409,717
FIELD EMISSION ARC DISCHARGE TUBE
Charles M. Slack, Glen Ridge, and Andrew
Pfeiifer and Clarence E. Dawley, Bloomfield,
N. J., assignors to Westinghouse Electric Cor
poration, East Pittsburgh, Pa., a corporation of
Pennsylvania
Application September 26, 1942, Serial No. 459,774
7 Claims. (o1. 25o-27.5)
l
2
The `present invention relates to discharge de
the electrostatic pull of the voltage from varying
the electrode spacing and causing erratic per
vices and more particularly to such devices
wherein operation is initiated by a “field emis
sion arc” as an electron source, and constitutes
formance.
Still iur-ther objects of the present invention
an improvement over the structure such as 5 will become obvious to those skilled in the art
shown in copending application, Serial No.
412,566, ñled Sept. 27, 1941, in the name of -Charles
M_ Slack, 4Louis F. Ehrke and Clarence E. Daw
le , and assigned to the same assignee as the
present invention.
by reference to the accompanying drawing
wherein:
Fig. l is a perspective View partly in section
and with parts thereof broken away to better
10 illustrate the device, and schematically shown in
In discharge devices of this type and as pointed
out in the above-identiiied copending applica
an `operating circuit;
Fig. 2 is a sectional view taken on the line
II-II of Fig. 1;
the high potential gradient at the cathode. The
Fig. 3 is a sectional View similar to Fig. 2 and
resulting electrostatic field in turn causes a mi 15 showing a slight modification which the elec
nute arc to forni between the starting electrode
trode structure may take;
and the cathode, apparently due to evolved me
Fig. 4 is a sectiona1 View similar to Fig. 2 and
showing another modification which the elect
tallic particles and the positive ion bombardment,
resulting from ionization of the evolved metal . trode structure may take;
tion, held emission of electrons occurs due to
vapor caused by the arc, forming a cathode spot 20
and a reduction in the space charge.
This causes
Fig. 5 is a sectional View similar to Fig. 2 and
showing a still further modification which the
the impedance oi the device to be so reduced
electrode structure may take, and
that an electron discharge is almost instantane
ously initiated between the cathode and the an
ode of the device.
Fig. 6 is a side fragmentary view showing some
of the electrodes after a period of operation oi
25 the device.
Referring now to the drawing in detail, the
discharge device 4 of the present invention as
shown in Fig. 1 comprises a vitreous envelope -5
provided with a pair of electrodes 6 and 'l shown
paramount importance. For example, it is de
sirable that loss of the‘evolved metallic particles 30 as of rectangular pieces of metal of substantially
from one of the electrodes in no way adects the
uniform cross-section, such as copper, gold, silver,
We have found that for extended useful life
and reliability of operation of discharge devices
of this type certain considerations become of
characteristics of the device‘and that a uniform
uranium, or the like, and riveted or otherwise
añixe'd to very rigid leading-in conductors 8 and
electrode spacing be maintained throughout life.
9 so that the free ends of the rectangular elec
It is accordingly an object of the present in
vention to provide a discharge device operating v35 trodes 6 and 'i are disposed in a veritcal plane
parallel to each other with a small spacing of
by iield emission of electrons and wherein the
the order of a .0l in. therebetween depending
same has a` relatively long commercially useful
`upon the voltage to be applied.
liie in comparison with such devices previously
y" The leading-in conductors 8 and I9 are each in
known to the art.
Another object of the present invention is the 40 turn welded, soldered, or otherwise secured to
metallic terminals l0 and Il. These terminals
provision of a discharge device operating by ñeld
may be of tantalum, molybdenum, or the like,
emission of electrons and wherein the operating
but preferably are of copper and as shown, these
characteristics of the device remain substantially
terminals l0 and li are provided with an en
constant during` a relatively long commercially
45 larged ñanged portion, the periphery of which
useful life.
_
is feather-edged and forms an hermetical seal
Another object of the present invention is the
with an annular projection l2 provided at the
provision of a discharge device operating by iield
bottom of the envelope.
emission of electrons and wherein the electrode
spacing is maintained substantially uniform
An anode electrode I3 of a refractory metal
throughout a relatively long commercially use 50 having a higher melting point than that of the
electrodes t and l, such as tungsten, molybdenum
ful life of the device.
or the like, is also provided interiorly of the en
A still further object of the present invention
is the provision of a discharge device operating
velope 5. As shown in Fig. 1, this anode is of
by" field emission of electronsl and wherein the ` substantially _U-shaped configuration and sup
electrodes arè'ri'gi‘dly supported~ so" asmto-- prevent 55 portedin an inverted posîtiori'bya rigid leading
2,409,717
3
in conductor I4 so that the sides of the anode
I3 are equi-distant on both sides of the elec
trodes 6 and 'I and overlap the gap between the
latter, as shown in Fig. 2, which allows an in
crease in the thickness of the electrodes 6 and
'I without reducing the accessiblity of the cur
rent ñow tothe anode. The ano-de leading-in
conductor I4 is secured to the top of the envelope
5 by a terminal I5 hermetically sealed to a pro
jection I6 in the same manner as the leading
in conductors 8 and 9.
After assembly of the device, it is exhausted to
loss of evolved material does not always occur
from the cathode 'I but, as we have found, from
the starting electrode 6 and, in fact, the cathode
'I may accumulate material so that after consid
erable operation the appearance of the electrodes
6 and ‘l may be somewhat as shown in Fig. 6
with the starting electrode 6 eaten away and a
deposit built up on the cathode l. For this rea
son it is desirable to reverse the connections to
10 the electrodes 6 and 'I so that the transfer of ma
terial will be in the opposite direction,
Thus
since the electrodes 6 and 'I are of uniform cross
a high degree of evacuation through an exhaust
section and of similar material, it is a simple
matter to operate ñrst one and then the other
oughly degasified as is customary in the art so
of the electrodes 6 and 'I as cathode, by changing
that satisfactory operation is entirely independ
the reversing switch 2| from its full line position
ent of vapor or gas present in the device. If de
to that shown in dotted lines in Fig. 1, and so ex
sired, however, a metal vapor such as mercury
tend the useful life of the device.
may be introduced into the envelope 5 prior to
It is also to be noted that while most of the
“tipping-off” at Il which also results in satisfac 20 electrode material is transferred from one of the
tory operation so long as its pressure is such that
electrodes 6 and l to the other, there is some of
the spacing between the electrodes is less (and
this material vaporized away. This accumulates
preferably many times less) than the mean free
on the anode I3 and in the absence of provisions
path of electrons in the vapor so that ignition
to the contrary, since in most instances it is de
and operation of the device is entirely independ 25 sirable to have the anode fairly closely spaced, a
ent of the mercury vapor present.
further reduction in the spacing would result
As illustrated in Fig. l, the electrode 6 consti
from the accumulated material on the anode,
tutes the starting electrode while the electrode l
thus changing the operating characteristics of
is the cathode. In order to initiate a discharge
the tube. For this reason it is preferable to em
between the Starting electrode 6 and the cath 30 ploy a refractory material which operates con
ode 1, a high tension transformer I8 is shown,
tinuously or intermittently at a temperature
the primary winding I9 of which may be oon
above the melting point of the material of which
nected to the customary commercial source of
the electrodes 6 and 'I -are composed. Moreover,
supply of 115-230 volts. The secondary wind
by the anode I3 overlapping the gap between the
ing 20 has one end grounded at 22 while the op 35 electrodes 6 and 'í allowance is thereby made for
posite end is connected to the terminal Iil
an increase in thickness of the electrodes 6 and
through one blade of a reversing switch 2I and
’l without reducing the accessibility of the cur
hence to the starting electrode 6. Inasmuch as
rent flow to the anode.
the device of the present invention is particular
It will thus be seen that although the spacing
ly operable as a control tube, a source of supply 40 between the electrodes is rather minute, their
tip I‘I with the various metallic parts being thor
such as a transformer 23 is shown which may
likewise have its primary winding 24 connected
to the customary commercial source of 115-220
volts.
The secondary winding 25 of this transformer
23 has one end thereof connected to ground at
25 and to the terminal Il through the remain
ing blade of the reversing switch 2|, thus con
necting to the cathode l, while the remaining
end of the secondary winding and a connection
from the anode terminal I5 extends to the
“load,” thus positioning the discharge device be
tween the source and the load in order that en
ergization of the latter may be controlled by the
device 4.
When it is desired to operate the discharge
device 4, a high voltage impulse is applied be
tween the starting electrode 6 and the cathode
i mounting is not as critical as might be supposed
since any irregularity in the spacing will be elim
inated after operation of the tube. Also through
out tube life a uniform spacing is maintained be
¿ tween the electrodes at all points. This follows
because any point that tends to become nearer
than another will cause the discharge to transfei
to such point with resultant vaporization of ma
terial and the discharge thus moves around con
stantly maintaining an equalized spacing.
For exceptionally long tube life electrodes in
parallel may be employed such as shown in Figs.
4 and 5. In these ñgures the starting electrode 6
and cathode 'I may be formed of a plurality of
- parallel metallic plates and the anode I3 formed
in the same manner as shown in Fig. l except that
tarily energizing the primary winding I9. This
it is provided with a plurality of tines disposed
between the parallel plates of the starting elec
trode 6 and cathode 'I and also overlapping the
'i from the transformer i8, such as by momen
causes ñeld emission of electrons from the cath
space therebetween.
ode 'I due to the high potential gradient atthe
cathode with the resulting electrostatic field
A still further requirement for stable operation
is rigidity of the electrode structure for if the
causing a minute arc to form between the start
electrode supports, and particularly the supports
ing electrode 6 and cathode 1 because of evolved
metal vapor. The positive ion bombardment re
sulting from ionization of the evolved metal par
ticles caused by the arc forms a cathode spot on
the electrode 1, and the impedance of the device
is so reduced that an electron discharge is almost
instantaneously initiated or transferred between
the closely spaced cathode -I and anode I3, re
sulting in the “load” being energized from the
for the starting electrode 6 and cathode 1, are not
sufficiently rigid, the electrostatic pull of the volt
age tends to affect the electrode spacing and
produce erratic performance. Although it is not
possible to state the exact amount of rigidity re
quired for all applications, it is believed preferable
to have rigidity greater than that obtainable with
100 mil diameter molybdenum three inches long.
Also to increase rigidity the leading-in and sup
porting conductors 8, 9, and I4 may be formed
high tension transformer 23~
Contrary to what might be expected, the net 75 as channels such as shown in Fig. 3 with the
2,409,717
5
electrodes 'ô and 1 welded or riveted thereto in
6
between with attendant evolution of metallic par
the same manner as when rods are employed.
ticles from one of said electrodes which build up
It thus becomes obvious to those skilled in the
on the adjacent surface of the other of said elec
art that a discharge device operable by field
trodes, a refractory metal anode positioned on
emission of electrons is herein provided in which
each side of said oppositely disposed electrodes
a substantially uniform electrode spacing and
and overlapping the space therebetween for sup
hence constant operating characteristics are
porting an electron discharge with one of the
maintained throughout a relatively long commer
electrodes of said pair immediately following the
cially useful life. Moreover, the device is of ex
ñeld emission arc discharge between said pair
ceptionally rigid construction so that electro l0 of electrodes and said anode being operable at
static pull of the voltage has no material affect
a temperature above the melting point of the
on the device, which still further contributes to
metal of said pair of electrodes to prevent ac
the elimination of erratic perfomance during
cumulation of evolved metallic particles from the
operation.
latter on said anode, and means for reversing
Although several embodiments of the present
current flow between said pair of electrodes to
cause the evolved metallic particles accumulated
invention have been shown and described, it is to
be understood that still further modifications of
on one of the electrodes of said pair to be re
the’ same may be made without departing from
turned to the other of said electrodes from which
the spirit and scope of the appended claims.
such particles originated.
5. A discharge device wherein operation is ini
We claim:
.
l. A discharge device wherein operation is ini
tiated by ñeld emission of electrons comprising a
pair of oppositely disposed spaced metallic elec
tiated by field emission of electrons comprising a
pair of oppositely disposed spaced electrodes
trodes each consisting of a plurality of parallel
between which a. field emission arc discharge oc
plates and between which electrodes a i'leld emis
sion arc discharge occurs upon the application
curs upon the application of a potential thereto,
and an anode positioned on each side of said op
of a potential thereto, and an anode provided
positely disposed electrodes and overlapping the
with a plurality of portions and positioned to dis
space therebetween for supporting an electron
pose a portion thereof on each side of the paral
discharge with one of the electrodes of said pair
immediately following initiation of the ñeld emis
sion arc discharge between said pair of electrodes.
2. A discharge device wherein operation is ini
tiated by ñeld emission of electrons comprising a
lel plates of said pair of electrodes and overlap
ping the space therebetween for supporting an
electron discharge with one of the electrodes of
said pair immediately following initiation of the
trodes between which a field emission arc dis
ñeld emission arc discharge between said pair of
electrodes.
6. A discharge device wherein operation is ini
charge accompanied by evolved metallic particles
tiated by ñeld emission of electrons comprising
occurs upon the application of a potential thereto,
and a refractory metal anode positioned on each
a pair of electrodes including metallic plates dis
posed in a common plane with their edges in
pair of oppositely disposed spaced metallic elec
spaced parallel relation to each other and between
side of said oppositely disposed electrodes and
overlapping the space therebetween for support 40 which a field emission arc discharge occurs upon
ing an electron discharge with one of the elec
the application of a potential thereto, and a sub
trodes of said pair immediately following initia
stantially U-shaped refractory metal anode po
sitioned to dispose its parallel portions substan
tion of the ñeld emission arc discharge between
tially equi-distant on each side of said pair of
said pair of electrodes and said anode being
operable at a temperature above the melting point 45 metallic plate electrodes and being of a width
greater than the spacing between said pair of
of the metal of said pair of electrodes to prevent
electrodes so as to overlap the latter and opera
accumulation of evolved metallic particles from
ble to support an electron discharge with one of
»
the electrodes of said pair immediately following
3. A discharge device wherein operation is ini
tiated by field emission of electrons comprising a 50 initiation of the field emission arc discharge be
tween said pair of electrodes.
pair of oppositely disposed spaced> metallic elec
7. A discharge device operable by field emission
trodes, means for applying a potential to said
of electrons comprising a pair of oppositely dis
electrodes of sufficient magnitude to cause the
the latter on said anode.
posed spaced metallic electrodes and between
initiation of a ñeld emission arc discharge there
between with attendant evolution of metallic par 55 which a field emission arc discharge occurs upon
the application of a potentia1 thereto, leading
ticles from one of said electrodes which build up
in and supporting conductors for said electrodes
on the adjacent surface of the other of said elec
having a rigidity greater than that attainable
trodes, an anode positioned on each side of said
with molybdenum of 100 mil diameter to pre
oppositely disposed electrodes and overlapping
the space therebetween for supporting an electron 60 vent the electrostatic pull of the voltage from
changing the electrode spacing and causing er
discharge with one of the electrodes of said pair
ratic performance of the device during operation,
as cathode immediately following initiation of
and a refractory metal anode supported by a
the ñeld emission arc discharge between said pair
leading-in conductor of equal rigidity as the lead
of electrodes, and means for reversing current
ing-in conductors for said pair of electrodes and
flow between said pair of electrodes to cause the
provided. with a portion thereof on each side of
evolved metallic particles accumulated on one
said pair of electrodes which portions overlap
the spacing therebetween and said anode being
operable to support an electron discharge with
particles originated.
4. A discharge device wherein operation is ini 70 one of the electrodes of said pair immediately fol
lowing the initiation of the field emission arc
tiated by field emission of electrons comprising a
pair of oppositely disposed spaced metallic elec
discharge between said pair of electrodes.
CHARLES M. SLACK.
trodes, means for applying a potential to said
of the electrodes of said pair to be re-transferred
to the other of said electrodes from which such
electrodes of sufficient magnitude to cause the
initiation of a field emission arc discharge there 75
ANDREW PFEIF‘FER.
CLARENCE E. DAWLEY.
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