Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2003-05-23
2004-08-10
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S448000
Reexamination Certificate
active
06774552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun for use with a traveling wave tube, a klystron and the like, and more particularly, to a Pierce type electron gun which has a Wehnelt electrode (also referred to as a “focus electrode”) for focusing an electron beam.
2. Description of the Related Art
A traveling wave tube and a klystron are electron tubes which rely on interaction of an electron beam emitted from an electron gun with a high frequency circuit for amplifying and oscillating microwaves. As illustrated in
FIG. 1
, for example, these electron tubes are each composed of electron gun
21
for emitting an electron beam; high frequency circuit
22
for promoting the interaction of the electron beam emitted from electron gun
21
with a high frequency signal (microwave); a collector
23
for capturing the electron beam delivered from high frequency circuit
22
; and anode electrode
24
for guiding the electron beam emitted from electron gun
21
into high frequency circuit
22
.
An electron beam emitted from electron gun
21
is introduced into high frequency circuit
22
by anode electrode
24
, and travels within high frequency circuit
22
while it interacts with a high frequency signal applied to high frequency circuit
22
. The electron beam delivered from high frequency circuit
22
is applied to collector
23
and captured by a collector electrode included in collector
23
. In this event, high frequency circuit
22
delivers a high frequency signal which is amplified through the interaction with the electron beam.
While many types of electron guns are known for use with such traveling wave tubes and klystrons, a Pierce type electron gun has a Wehnelt electrode for focusing an electron beam, as one of such electron guns.
FIG. 2
is a lateral sectional view illustrating the structure of a conventional Pierce type electron gun.
As illustrated in
FIG. 2
, the conventional Pierce type electron gun comprises cathode
11
for emitting electrons; and a Wehnelt electrode
15
for focusing electrons emitted from cathode
11
.
Cathode
11
is made of a discal porous tungsten base impregnated with an oxide (emitter material) of barium (Ba), calcium (Ca), aluminum (Al) or the like, and is bonded to cylindrical heater cap
12
made of molybdenum (Mo) or the like by welding or brazing to seal an open end thereof. Cathode
11
should be formed thick enough to endure the welding or brazing temperature and facilitate the bonding of cathode
11
to the cylindrical inner wall of heat cap
12
at a right angle. A heater, not shown, is disposed within heater cap
12
for applying thermal energy for emitting electrons from cathode
11
.
Wehnelt electrode
15
is formed in a troidal shape having an opening at the center by cutting a metal material such as molybdenum, and bonded to one open end of Wehnelt support
14
formed in a cylindrical shape by welding or brazing.
Heater cap
12
mounted with cathode
11
is supported in Wehnelt supporter
14
, for example, in a tripod structure, by metal supporters
16
made of tantalum (Ta), molybdenum (Mo), molybdenum-rhenium (Mo—Re) alloy, iron-nickel-cobalt alloy (koval:Kv), or the like, and fixed at a position at which an electron emitting surface of cathode
11
is substantially coplanar with the surface of Wehnelt electrode
15
. As illustrated in
FIG. 2
, Wehnelt electrode
15
is formed such that its surface closer to anode electrode
19
has an angle of approximately 67.5 degrees to the outermost shell of electron beam
18
(referred to as the “Pierce angle”).
Wehnelt supporter
14
, which contains heat cap
12
mounted with cathode
11
, is securely fixed within an electron gun housing for vacuum encapsulation.
In the foregoing Pierce type electron gun, Wehnelt electrode
15
is applied with the same potential as cathode
11
to make a focusing action which shapes electrons emitted from cathode
11
into a beam which is introduced into the high frequency circuit (see
FIG. 1
) by anode electrode
19
.
In the conventional Pierce type electron gun, an electrode spacing between the cathode and Wehnelt electrode, and an electrode spacing between the cathode and anode electrode, i.e., perveance must be made consistent with design values with high accuracy in order to focus electrons emitted from the cathode within a desired beam diameter. Particularly, it is critical to satisfy a dimensional accuracy for a narrow spacing between the cathode and Wehnelt electrode.
A large perveance between the cathode and Wehnelt electrode would give rise to collision of electrons emitted from the cathode with the anode electrode, and a varying diameter of an electron beam within the high frequency circuit to cause uneven interaction with a high frequency signal, resulting in increased power consumption, degraded amplification performance, and the like of the traveling wave tube.
In the structure of the conventional Pierce type electron gun illustrated in
FIG. 2
, it is quite difficult to integrally form the Wehnelt electrode, Wehnelt supporter and metal supporters through cutting operations, so that the Wehnelt electrode, heater cap, metal supporters and Wehnelt supporter are separately formed and bonded to one another by welding, brazing or the like. Thus, the conventional Pierce type electron gun has disadvantages of a larger number of parts and a long time required for assembling. In addition, since a larger number of parts causes an increase in dimensional errors of respective parts, mounting errors and distortion associated with bonding, and the like, it is difficult to limit the perveance of the cathode and Wehnelt electrode within a predetermined value.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a Pierce type electron gun which prevents an increase in power consumption of a heater and an increase in perveance, and is composed of a fewer number of parts to facilitate its assembly.
To achieve the above object, an electron gun according to the present invention has a cathode for emitting electrons, a heater cap which contains a heater for applying the cathode with thermal energy for emitting electrons, a retainer for securing the cathode on the heater cap by holding the peripheral edge of the cathode to the heater cap, and a cylindrical Wehnelt supporter that has a Wehnelt electrode for focusing an electron beam formed in such a shape that an average angle of the surface thereof with respect to an outermost shell of said electron beam matches a Pierce angle, and three or more heater cap supporters for securely supporting said heater cap at a position at which an electron emitting surface of said cathode and an opening formed through said Wehnelt electrode satisfy a predetermined perveance.
Thus, the number of parts is reduced by integrally forming the Wehnelt supporter, Wehnelt electrode and heater cap supporters, resulting in a reduction in dimensional error of each part, mounting errors and distortion associated with bonding, and the like. Consequently, the perveance of the cathode and Wehnelt electrode is readily limited within a predetermined value. In addition, since the Wehnelt supporter including the Wehnelt electrode and heater cap supporters can be formed through pressing, less time is required for machining respective parts and assembling these parts into the Wehnelt supporter, and the cost is also reduced for the electron gun.
Also, in the present invention, each of the heater cap supporters is formed by cutting out the cylindrical side surface of the Wehnelt supporter in a strip shape except for one short side. In this event, the short side, left uncut, is one of sides parallel with the circumferential direction of the Wehnelt supporter, which is closer to the Wehnelt electrode. By thus forming the heater cap supporters in a strip shape except for the side closer to the Wehnelt electrode, heat radiated from the heater cap is prevented from leaking from strip-shaped openings formed through the side surface of the Wehnelt supporter, thereby sa
NEC Microwave Tube, Ltd.
Patel Vip
Sughrue & Mion, PLLC
Zimmerman Glenn
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