Series diode X-ray source

A multiple cathode-anode pulsed X-ray source utilizes a first X-ray transparent cathode spaced apart from a solid tungsten first anode between which is disposed a second tungsten anode spaced apart from the first cathode and electrically connected to a second X-ray transparent cathode which is also spaced apart from a solid tungsten first anode. Electrons emitted from the first cathode are caused to bombard the second anode to emit X-radiation therefrom where the electrons are then conducted to and emitted by the second cathode to bombard the first anode to again emit X-radiation therefrom. The X-radiation emitted from the first and second anodes passes through the first and second cathodes to a target.

BACKGROUND OF THE INVENTION 
This invention relates generally to X-ray sources, and in particular to 
multiple cathode-anode X-ray sources. 
The multiple cathode X-ray tubes of the prior art generally used the 
multiple cathodes to produce separate energy level X-rays or multiple 
images to achieve a three-dimensional perspective for better analysis of 
the subject being irradiated. 
Other multiple anode X-ray sources were used to create a uniform or 
homogenious X-ray field by the arrangement of the various anodes. Such 
sources were particularly adapted to irradiate various substances to alter 
their physical, chemical or biological characteristics. 
Still other dual or multiple cathode X-ray sources used each cathode for 
different purposes such as one cathode for fluoroscopy purposes and the 
other cathode for direct photography. 
In all the prior art X-ray sources, the total current accelerated was equal 
to that provided by the Generator. The present invention provides a method 
of accelerating currents greater than the generator current by using the 
generator current more than once. 
SUMMARY OF THE INVENTION 
The apparatus of the present invention has low voltage diode X-ray sources 
arranged in a series configuration. The apparatus of the present invention 
thus includes the advantage of using the generator current more than once 
by driving multiple cathode-anode sources in series. 
A further advantage of the apparatus of the present invention includes 
providing a dual feed configuration. The opposing magnetic fields of the 
dual feeds reduce the pinch effect a high current densities and thus 
reduces the loss of electrons bypassing the intermediate electrode. 
Basically, the X-ray source of the present invention comprises a first 
X-ray transparent cathode which is spaced apart from a first anode, 
between which is disposed an electrically floating second anode which is 
electrically connected to a second X-radiation transparent cathode. 
Electrons from an electrical current source are caused to be emitted from 
the first cathode and bombard the second anode to emit X-radiation. The 
electrons are then conducted to the second cathode where they are caused 
to be emitted and bombard the first anode to emit X-radiation. 
A further embodiment of the present invention utilizes a dual current feed 
to the first cathode and, because of inductance considerations, a dual 
feed to each subsequent cathode. 
It is, therefore, an object of the present invention to provide a multiple 
cathode-anode X-ray source. 
It is another object of the present invention to provide a multiple 
cathode-anode X-ray source by which the generator current is used more 
than once. 
It is another object of the present invention to provide a source of 
X-radiation having a high intensity output at a low voltage. 
It is still a further object of the present invention to provide a source 
of X-radiation having an efficient transformation of electrical energy 
into X-radiation. 
It is still a further object of the present invention to provide an X-ray 
source utilizing a dual current feed to the cathodes by which low voltage, 
high current density multiple cathode-anode X-ray sources can be used in 
series. 
These and other objects of the present invention will become manifest upon 
study of the following detailed description when taken together with the 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 1, there is illustrated a first embodiment of the 
X-ray source of the present invention comprising, basically, a first 
cathode 12, a first tungsten anode 14 disposed parallel to and spaced 
apart from cathode 12, a second tungsten anode 16 electrically connected 
to second cathode 18, also disposed parallel to and spaced apart between 
first cathode 12 and first anode 14. A vacuum tight, X-ray transparent 
housing 20 is arranged to enclosed the multiple cathode-anode 
configuration of FIG. 1 and is evacuated to a high vacuum by means of 
vacuum pumps (not shown) well known in the art. Also, diode impedance is 
decreased because 
First cathode 12 defines a generally planar X-ray transparent grid and is 
connected about its outer periphery to the negative side of a source of 
electrical current (not shown) common in the art, through electrical 
conducting members 21 and 22. Insulators 23 or radiused ports are used to 
electrically insulate conductors 22 where they pass through electrical 
conducting plate 24. 
Electrical conductors 22 are arranged as extended members electrically 
connecting the end of cylindrical conductor 21 to first cathode 12. 
Although conductors 22 are shown connected to conductor 21 proximate 
conducting end plate 30, the end of cylindrical conductor 21 could extend 
to a point near insulators 23 before being connected to conductors 22 in 
order to take full advantage of its coaxial relationship to outer 
cylindrical conductor 26. 
First anode 14 is electrically connected to the ground side of previously 
referred to electrical current source (not shown) common in the art, 
through electrically conducting plate member 24 which is, in turn, 
electrically connected to electrically conducting cylindrical member 26. 
Electrically conducting cylindrical member 26 is also arranged to be 
coaxial with cylindrical conductor 21 being spaced apart therefrom by 
electrical insulator spacer members 28. 
A conducting end plate 30 is used to maintain the end portion of conducting 
member 22 in a cylindrical shape, and, together with insulators 28 and 
conductors 26, serves as a liquid-to-vacuum seal. 
Second anode 16 is held in spaced apart relation between first cathode 12 
and first anode 14 by means of insulated spacer blocks 32. 
Electron emission for the cathodes can be controlled through various 
techniques such as surface heating, surface conditioning or by 
cathode-anode spacing. 
In the illustrated embodiment, electron emission from first cathode 12 to 
second anode 16 is controlled by the spacing of the surface of second 
anode 16 from first cathode 12 which is less than the spacing of second 
cathode 18 from first cathode 12. The same is true for the spacing of 
second cathode 18 from the surface of first anode 14 which is less than 
the spacing of the back of second anode 16 from conducting plate 24. 
With reference to FIG. 2, first cathode 12 comprises a peripheral support 
ring 40 on which are attached electrically conductive wires 42 spaced 
apart from each other to define a grid to permit the X-radiation emitted 
from second anode 16 and first anode 14 to pass therethrough. 
Still with reference to FIG. 2, second cathode 18 comprises an inner 
support ring 46 on which is attached one end of spaced apart electrically 
conductive support wires 48 in the manner of spokes of a wheel. The other 
end of support wires 48 are attached to the underside of second anode 16. 
For additional rigidity and support, a conductive support wire or rod 50 is 
located at equi-angular spacing and attached to both second anode 14 and 
inner support ring 46. 
Second cathode 18 thus defines a generally X-ray transparent annular ring 
comprising a plurality of fine, spaced apart wires arranged spoke-like to 
allow X-rays emitted by first anode 14 to pass therethrough. 
To operate the apparatus of FIGS. 1 and 2, a pulse of electrical current 
(negative) from an electrical current source (not shown) common in the 
art, is caused to flow through inner cylindrical conductors 21 and 22 in 
the direction of arrows 60. 
Upon reaching first cathode 12, the electrical current then disperses 
through the wire grid formed by conductors 42, where the electrons are 
caused by the potential difference between anode 16 and cathode 12 to be 
emitted therefrom toward second solid tungsten anode 16, as shown by 
arrows 62, to bombard the surface of anode 16 and emit X-radiation 
therefrom as indicated by wave symbol 64. 
The current is then conducted from second anode 16 to conducting wires 48 
and 50 of second cathode 18, as indicated by arrows 66, where the 
potential difference between anode 14 and cathode 18 causes electrons to 
be emitted from cathode 18 as indicated by arrows 68 and bombard the 
surface of first solid tungsten anode 14 to emit X-rays therefrom as 
indicated by wave symbol 70. 
The current then returns to the ground side of the electrical current 
source (not shown), as indicated by arrows 72, through outer conductor 26. 
Electrons are accelerated twice in separate diodes in series for greater 
utilization of generator current. 
Although the X-ray source configuration of FIGS. 1 and 2 will provide an 
efficient utilization of generator current, where it is desired to utilize 
high current densities and have a relatively low impedance, there is a 
potential limitation in the use of such a configuration. This limitation 
is due to the self-magnetic fields created by the high density current 
which tends to pinch the electron beam toward the center of the 
configuration along axis of rotation or centerline 80 (FIG. 1). This could 
result in the pinching of the beam of electrons emitted from first cathode 
12 toward centerline 80 and first anode 14, causing the emitted electrons 
to bypass second anode 16. For such higher current densities, the X-ray 
source configuration of FIGS. 3 and 4 can be used. 
With reference to FIG. 3, there is illustrated a cross-sectional 
elevational view of a further embodiment of the multiple cathode-anode 
X-ray source of the present invention in which the inner diameter of the 
first anode is greater than the outer diameter of the second anode. This 
configuration is used to achieve higher density electrical currents and 
avoid the tendency of the electron beam emitted from the cathodes to pinch 
towards centerline or axis of rotation of the circular configuration. 
FIG. 4 is a partial cut-away view of the apparatus of FIG. 3 taken at lines 
4--4. 
With reference to FIG. 3, the second embodiment of the X-ray source of the 
present invention comprises, basically, a first X-ray transparent cathode 
112, a first solid tungsten anode 114 disposed parallel to and spaced 
apart from cathode 112, a second solid tungsten anode 116 electrically 
connected to second X-ray transparent cathode 118 also disposed parallel 
to and spaced apart between first cathode 112 and first anode 114. A 
vacuum tight housing 120 is arranged to enclose the multiple cathode-anode 
configuration of FIG. 3 and is evacuated to a high vacuum by means (not 
shown) well known in the art. 
First cathode 112 is connected about its outer periphery to the negative 
side of a source of electrical current (not shown) common in the art, 
through electrical conducting members 121 and 122. 
Insulating members 123 are used to electrically insulate electrical 
conductors 122 from conductor 126. 
Anode 114 is electrically connected to the ground side of the previously 
referred to electrical current source (not shown) common in the art, 
through electrical plate member 124 which is, in turn, electrically 
connected to electrically conductive cylindrical member 126. 
Electrically conducting cylindrical member 126 is arranged to be coaxial 
with conductor 121 utilizing electrical insulation spacer member 128 to 
maintain the coaxial relationship throughout its length. 
A conducting end plate 130 is used to maintain the end portion of 
conducting member 122 in a cylindrical configuration. 
Electrical conductors 122 are connected about the peripheral rim of first 
cathode 112 and extend to electrically connect cylindrical conductor 121 
to first cathode 112. Although conductors 122 are shown connected to 
cylindrical conductor 121 proximate conducting end plate 130, the end of 
cylindrical conductor 121 could extend to a point near insulators 123 
before being connected to conductor 121 in order to take full advantage of 
its coaxial relationship to outer cylindrical conductor 126. 
In addition, a conducting post member 131, disposed coincident with the 
axis rotation or centerline 180 of the apparatus, is electrically 
connected to conducting end plate 130 and the center of first cathode 112. 
Second anode 116 is held in spaced apart relation between first cathode 112 
and first anode 114 by insulated spacer block 132 which is also attached 
to conducting post member 131. As an alternative, second anode 116 could 
be supported by an insulated block or post member attached to conducting 
end plate 130. 
With reference to FIG. 4, first cathode 112 comprises a peripheral spacer 
ring support 140 on which are attached electrical conducting wires 142 
spaced apart from each other to permit the X-radiation emitted by second 
anode 116 and first anode 114 to pass therethrough. 
Still with reference to FIG. 4, second cathode 118 comprises an outer 
support ring 146 on which is attached one end of spaced apart electrically 
conductive support wires 148. The other end of support wires 148 is 
attached to the underside of second anode 116. 
For added rigidity and support, conducting support rods or wires 150 are 
located at equi-angular spacing and are attached to both second anode 114 
and outer support ring 146 in a like manner as wires 148. 
Second cathode 118 thus defines a generally X-radiation transparent annular 
ring to allow X-rays emitted by first anode 114 to pass therethrough. 
The operation of the apparatus of FIGS. 3 and 4 is similar to that for 
FIGS. 1 and 2, however the current flow is markedly different to avoid the 
pinching effect of high current densities. 
In the apparatus of FIGS. 3 and 4, a pulse of electrical current (negative) 
from an electrical current source (not shown) common in the art, is caused 
to flow in inner cylindrical conductor 121 in the direction of arrows 160. 
Upon reaching the junction of conducting end plate 130 and conductor 122, 
the current flow is divided as shown by arrows 162 and 164, with a portion 
of the current, as indicated by arrows 162, travelling to the center 
portion of conducting end plate 130 where the current is then conducted 
through electrically conducting post 131, as indicated by arrows 166. The 
current flowing in conducting member 122, as shown by arrows 164, 
continues on to the outer peripheral conducting support 140 of first 
cathode 112 where it is then dispersed through the grid defined by 
conducting wires 142, as shown by arrow 168. 
Concurrently, the current passing through conducting post 131, as shown by 
arrows 166, also flows into and is dispersed through the grid defined by 
wires 142 of first cathode 112, as shown by arrows 170. 
Upon entering first cathode 112, the electrical current dispersed through 
the wire grid formed by conductors 142 is then caused to be emitted 
therefrom toward second anode 116, as shown by arrows 172, to bombard the 
surface of anode 116 to emit X-radiation as indicated by the wave symbol 
174. 
The current is conducted from second anode 116 to second cathode 118 and 
through conducting wires 148 and 150 as indicated by arrows 176, to be 
emitted from second cathode 118 to bombard the surface of first anode 114 
and emit X-radiation, as indicated by wave symbol 82. 
The current then returns to the ground side of the current source (not 
shown) as indicated by arrows 184 through electrical conducting plate 124 
and cylindrical conducting member 126. 
Thus electrons are accelerated twice in separate diodes in series for 
greater utilization of generator current. 
It will be noted that the current following parallel paths through central 
conducting post 131 and cylindrical arranged conducting members 122 tends 
to reduce the magnetic field in the area of second cathode 118 and second 
anode 116, thus reducing the pinch effect at high current densities. As 
can be seen in FIGS. 3 and 4, the magnetic fields created by the high 
current flow not only tending to pinch the beam inwardly, such as the 
current through conductors 122, but there are also created magnetic fields 
which tend to pinch the beam outwardly, such as the magnetic field caused 
by the current through central post member 131. The combined result is the 
containment of the electron beam on the annular anode surfaces. 
In addition, the two current feeds in parallel yield a lower inductance 
than either mode alone. Impedance is decreased because each dual feed 
diode is really two diodes in parallel. 
For the configurations of FIGS. 3 and 4, central conducting post member 131 
could be removed and anode 116 extended to the centerline 180. This, of 
course, would increase the pinch effect on the anodes, because of the 
higher magnetic field associated with the single current path. Any 
pinching of the beam of electrons coming from cathode 118 may cause a 
portion of the electrons to miss first anode 114 inside the inner diameter 
of anode 114 and behind second anode 116. There would be only a loss in 
utilization of electrons. The electrons from second cathode 118 would be 
deflected toward axis of rotation or centerline 180 and would therefore be 
lost from bombardment of first anode 114. 
With reference to FIGS. 5, 6 and 7, there is illustrated a representation 
of an X-ray pin-hole camera picture of the surface of first anode 114 and 
second anode 116 of the dual feed configuration of FIGS. 3 and 4. The dots 
or stippling represent the intensity of X-radiation which, of course, is 
generally proportional to the number or density of electrons bombarding 
each anode. 
By adjusting the ratio of outer current I(o) feeding the outside edge of 
first cathode 112 though peripheral spacer ring support 140, to inner 
current I(i) feeding first cathode 112 through conducting post member 131, 
the concentration of electrons by the magnetic pinch effect can be 
controlled. 
As previously described, if conducting center post 131 were removed and the 
inner diameter of second anode 116 reduced to centerline 180 thus 
enlarging the surface area of anode 116, the pinch effect on the electrons 
emitted by cathodes 112 and 118 would be increased. This would case a 
portion of the electrons emitted by cathode 118 to miss first anode 114 
and flow inside the inner diameter of anode 114 and behind anode 116. 
With reference to FIG. 5, the X-radiation distribution is shown where the 
ratio of outer current I(o) to inner current I(i), I(o)/I(i), is 1.3. The 
pinch effect caused by the flow of current in central conducting post 131 
tends to cause the flow of electrons emitted from cathode 112 and 
accelerated to anode 116 to move radially away from central conducting 
post 131 and strike, for the most part, the area of anode 116 proximate 
its outer peripheral edge. The inner edge of anode 116 is shown to emit 
little, if any, X-radiation indicating few electrons are bombarding this 
region of the anode. 
With reference to FIG. 6, the X-radiation distribution is shown where the 
ratio of outer current I(o) to inner current I(i), I(o)/I(i), is 1.7. The 
pinch effect caused by the current in central conducting post 131 is 
almost equal to the pinch effect caused by the flow of current in outer 
conductors 122. The X-radiation and, therefore, electron density, is 
fairly evenly distributed over the entire surface of anodes 116 and 114. 
With reference to FIG. 7, the X-radiation distribution is shown where the 
ratio of outer current I(o) to inner current I(i), I(o)/I(i), is 2.8. The 
pinch effect caused by the current in outer conductors 122 is greater than 
the pinch effect caused by the current in inner conducting post 131. Thus, 
the electrons emitted by cathodes 112 and 118 are caused to flow toward 
centerline 180 and, for the most part, bombard the inner edges of anodes 
114 and 116 as shown by the greater density of stippling in FIG. 7. 
Thus, by controlling the ratio of current flow between the inner and outer 
current feed paths, such as, by varying the inductive reactance of those 
paths, the vector motion of the electrons emitted by the cathodes can be 
controlled to provide full utilization of the electrons at the anodes. For 
example, this inductive reactance can be adjusted by decreasing or 
increasing the diameter of conducting post 131, or by increasing or 
decreasing the number of conductors 122, or by employing flux excluders in 
the region of current arrows 162 and 168. The ratio of current in the 
inner current feed path defined by arrows 162 and 170, relative to the 
outer current feed path defined by arrows 164 and 168, will be inversely 
proportional to the inductive reactance of these two paths. Thus, by 
increasing the inductive reactance of the current feed path defined by 
arrows 162 and 170, the current through central electrode will be reduced. 
In a like manner, by increasing the inductive reactance in the current 
feed path defined by arrows 164 and 168, the current to outer peripheral 
conducting support 140 will be reduced. 
It can be seen that the dual current feed configuration of FIG. 3 can also 
be applied to the double diode arrangement of FIG. 1. As in the case of 
the dual diode feed configuration of FIG. 3, the ratio of inner to outer 
currents must be adjusted to prevent the "pinch" from causing electrons to 
be deflected away from anodes 14 and 16.