US2728029A - Interdigital magnetron - Google Patents

Description

Dec. 0, 1955 P. R. FINGER INTERDIGITAL MAGNETRON Filed May 11, 1950 INVENTOR. Paul RFmger United States Patent O INTERDIGITAL MAGNETRON Paul R. Finger, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application May 11, 1950, Serial No. 161,387

3 Claims. c1. 31539.73)

This invention relates in general to inter-digital magnetrons, and in particular to a magnetron which has liquidcooled fingers.

Inter-digital magnetrons have been used, but two adverse eilects are noticed:

1. The fingers become too warm, and

2. The cathode couples a great deal of energy from the magnetron cavity due to antenna action.

It is an object of this invention, therefore, to provide an interdigital magnetron which has liquid-cooled fingers.

A further object of this invention is to provide an interdigital magnetron which has shorting bars with polarities such as to counteract the antenna effect of the center cathode.

Yet another object of this invention is to provide a magnetron which has inter-digital members fluidly connected in an economical and practical manner.

A feature of this invention is found in the provision to an interdigital magnetron comprising a center cathode, an annular resonating anode structure supported about the cathode, which has a meshing conduit system that serves as the inter-digital radio frequency inducing members.

Further objects, features, and advantages of this invention will become apparent from the following description and claims when read in view of the drawings, in which;

Figure 1 represents a cut-away view of the inter-digital magnetron of this invention showing the relative spatial relationship among the various parts;

Figure 2 is a sectional view taken on line 22 of Figure 1 illustrating how the inter-digital members are spaced relative to each other; and,

Figure 3 is a detailed view of the indirectly heated cathode.

Figure 1 shows an inter-digital magnetron which has a portion cutaway so as to illustrate more clearly the internal structure of the tube. An external air-tight cover of a generally cylindrical shape encloses the tube. A mag netic pole 11 extends through the top of the container-10 and a second magnetic pole 12 extends through the bottom of the container. Magnetic means, not shown, complete the magnetic circuit externally of the container 10 between the poles 11 and 12. The pole 12 is formed with an axial opening 15 through which extends a cathode support member 13. A suitable vacuum seal exists between the pole 12 and support 13. The upper end 14 of the cathode support is indirectly heated by a heating coil, as shown in Figure 3, and furnishes the electron supply for the tube. The support 13 is hollow and contains a rod 16 which is insulated from and supported within the support 13. The rod 16 terminates adjacent the upper end of the support 13 and a resistance member 17 is connected between the rod 16 and the active portion 14. An opening 18 is formed in the support member 13 within the confines of the container 10 to allow the interior of the tube to be evacuated. The end members 16 and 13 are sealed by glass or other suitable material.

A generally hollow annular-shaped member 19 is sup ported within the container and attached to the container walls by support means 21. A cross section of the annular member 19 is of a generally U shape with the open side of the U pointing toward the active portion 14 which forms the cathode of the tube. A direct current potential is impressed between the cathode 14 and the annular member 19. This may be accomplished by impressing a high negative potential on the support 13 through an external circuit and by grounding the container 10 which may be electrically connected to the annular member 19. This high direct current potential tends to accelerate electrons emitted from the cathode 14 towards the annular member 19. A magnetic field is impressed between the pole pieces 11 and 12, and thus the emitted electrons are acted upon by the magnetic and electric fields combined. The strengths of the fields are adjusted so that the electrons will have a generally spiralling path from the cathode; some falling back into the cathode, while others reach the anode 19.

A plurality of inter-digital fingers are formed by the conduit means illustrated in Figure 1. For illustrative purposes, a structure with eight fingers is shown, but it is to be understood that any number of fingers may be used. One half of the fingers are attached to the upper edge 22 of the annular member 19, and the other half of the fingers are connected to the lower surface 23 of the annular member 19. A fluid inlet conduit 24 is ring-shaped and supported within the container 10 above the top surface 22. An outlet conduit 26 is also supported above the surface 22. Likewise, a second inlet pipe 27 is supported within the container adjacent the wall 23 and a second outlet pipe 28 is supported adjacent pipe 27. Connected to the inlet pipe 24 is a tube 29 which bends down to contact the wall 22 and extends radially to the internal opening of the annular member 19. The tube 29 passes transversely down the open side of the annular member 19 to a point beyond the end wall 23, but it does not contact the wall 23. A chord 31 of the tube 29 extends approximately of the circumference of the central opening be fore passing upwardly to contact the upper Wall 22 and to the outlet pipe 26. The tube 29 is electrically connected to the upper wall 22 adjacent the upper ends 32 and 33 respectively, but does not make electrical contact with the end Wall 23. A second tube 34 is connected to the pipe 24 and extends down through the anode cavity and back to the outlet pipe 26 in a manner similar to the first tube 29. The tube 34 is spaced so as to be symmetrical with the tube 29 and on the opposite side of the annular member 19. As is best shown in Figure 2, a pair of tubes 36 and 37 extend upwardly through the central opening formed in the annular ring 19 and have their inlet and outlet ends connected to the headers 27 and 28 respectively. The tubes 36 and 37 are electrically connected to the inner edge of the wall 23 but, as shown in Figure 2, do not engage the upper Wall 22. Strapping strips of conducting material 38 connect the upper ends of tubes 36 and 37 together so that they may be maintained at the same electrical potential. Likewise, straps 39 connect the lower corners of tubes 29 and 34.

Water is supplied to the inlet rings 24 and 27, and is removed through the outlet rings 26 and 28, respectively. Water flows between the rings 24 and 26 through the tubes 29 and 34. The vertical portions of the tubes comprise active portions or" the anode and have radio frequency current induced in them during operation. These induced currents tend to heat the active portions and limit the maximum power obtainable from the magnetron. The cooling fluid flowing through the tubes will remove heat from them, and thus allow the maximum energy to be greatly increased.

Another advantage of this invention is that the upwardly extending cathode 13 which has its active portion 14 within the power generating cavity acts as an antenna, and

normally couples a great deal of energy from the device. It has been customary prior to this invention to put external choke coils about the support 13 to choke the high frequency energy and thus keep it from being lost through the cathode connection. The efficiency of the apparatus, therefore, has not been high. Applicants structure with the horizontal cross portions of the tubes 29 and 34 and the straps 38 will eliminate this antenna effect. As shown in Figure 2, the cross portions of the tubes and straps 38 adjacent the upper wall 22 of the annular member 19 are electrically connected to the lower wall 23 of the annular member, and thus are maintained at this potential. The upper wall 22 and the lower wall 23 are 180 degrees out of phase and it is this phase relationship which normally induces currents in the cathode supports 13. Because of the electrical connection of the straps 38 and the horizontal portions of the tube, the capacitive effect of the end walls 22 and 23 will be counter-balanced by the straps 3S and the horizontal portions of the tubes. The spacings of the tubes may be adjusted so as to cause complete cancellation of the antenna effect.

In operation the magnetron illustrated in Figure 1 will run relatively cool, due to the coolant flowing through the inter-digital tubes. Thus, the power output may be safely increased. The output energy is removed from the magnetron by the coupling loop 41 in a well known manner. At the same time the efiiciency of the tube will be increased because of the cancellation of the antenna effect of the cathode support 13 which is accomplished by the horizontal portions of the tube and the joining strips. Since they are connected to end walls which have opposite polarity, they will tend to cancel the capacitive effect upon the cathode support. Since the horizontal portion of the tubes and the straps are nearer to the cathode support than are the end walls 22 and 23, it is not necessary that they have as large an area or as strong a field as exists between the end walls.

Although this invention has been described with respect to a preferred embodiment, it is not to be so limited as changes and modifications may be made herein which are Within the full intended scope of the invention, as defined by the appended claims.

I claim:

1. A magnetron comprising, an annular anode having first and second axially spaced walls for terminating a first axially directed electric field and an outer wall defining a resonant cavity, an axially extending cathode, said anode and said cathode being coaxially disposed and defining an interaction space therebetween, means for exciting said cavity with radio frequency oscillations, a first set of axially extending anode segments disposed adjacent the inner periphery of said annular anode, each of said segments electrically connected at one end to the first of said axially spaced walls and spaced at the other end from the second of said axially spaced walls, a second set of axially ex-.

tending anode segments interdigitally disposed with respect to said first set of segments and electrically connected at one end to the second of said axially spaced walls and spaced at the other end from the first of said axially spaced walls, means electrically connecting the said other ends of each of said sets of segments together, said means terminating a second electric field directed oppositely to said of hollow anode fingers being electrically connected at one end to said first wall and being electrically connected at the other end by a hollow portion so that cooling fluid may flow therethrough, said portion extending adjacent the plane of said second wall, with said other ends and said portion spaced from said second wall, said second pair of hollow anode fingers being electrically connected at one end to said second wall and being electrically connected at the other end by a second hollow portion so that cool- 7 ing fluid may flow therethrough, said second portion extending adjacent the plane of said first wall, With said other ends and said second portion spaced from said first wall,

' and means for supplying cooling fluid to said pairs of fingers.

3. In an interdigital magnetron having a central axially extending cathode and a coaxial annular anode including a pair of axially spaced walls and being of a generally U shape in cross section, interdigital means comprising a first tube connected to the first wall of said anode and having a first portion extending axially through the anode cavity, a second portion extending transversely through the anode cavity and a third portion extending axially through the cavity to said first wall, a second tube connected to the second anode wall and having a first portion extending axially through the anode cavity, a second portion extending transversely through the cavity and a third portion extending axially to connect to the second anode wall, said first tube spaced from said second anode wall, said second tube spaced from said first anode wall, a first input manifold connected to one end of said first tube to supply cooling fluid thereto, a first exhaust manifold connected to the opposite end of said first tube to remove the fluid therefrom, a second input manifold connected to one end of said second tube to supply cooling fluid thereto, and asecond exhaust manifold connected to the opposite end of said second tube to remove the fluid therefrom.

References Cited in the file of this patent UNITED STATES PATENTS Brown Oct. 21, 1952

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