US3227904A - Collector for electron beam tube - Google Patents

Description

Jan. 4, 1966 M. E. LEVIN COLLECTOR FOR ELECTRON BEAM TUBE Filed April 9, 1962 IN V EN TOR.

MART/N E, LEVIN ATTORNEY United States Patent 0 3,227,994 CGLLECTGR FOR ELECTRON BEAM TUBE Martin E. Levin, Millbrae, (Ialifi, assignor to Eitel- McEullough, Inc, San Carlos, Calif a corporation of California Filed Apr. 9, 1962, Ser. No. 185,966 4 Claims. (Cl. 313-21) This invention relates to collector electrodes for electron beam tubes, and particularly to a fluid cooled collector electrode.

Collector electrodes for high power electron beam tubes are usually fabricated from one or more copper billets hollowed to provide a chamber within which the electron beam is trapped. The exterior of the billets are sometimes provided with spiral channels for the passage of fluid coolant around the collector to effect a transfer or" heat from the metallic collector block to the fluid coolant. Collectors fabricated in this manner are frequently either difficult to fabricate and therefore expensive, or are inefficient. Accordingly, it is one of the important objects of the present invention to provide a collector which is economical to manufacture and relatively inexpensive, and which is extremely efiicient in the dissipation of heat.

High power electron beam tube collectors which are required to dissipate large amounts of power are usually large in physical dimensions, and require the passage therethrough of large volumes of fluid coolant to effectively dissipate the required power. Such collectors also require that substantial pressure he applied on the fluid coolant in order to provide the required velocity to effect efficient heat transfer. It is therefore another of the objects of this invention to provide a compact collector utilizing a relatively small volume of fluid coolant at relatively low pressure but with sufiicient velocity to provide turbulent flow.

Another problem often encountered is the tendency to develop zones of unequal heating and heat conduction through the metallic collector block. It is therefore a still further object of the invention to provide a collector in which there is substantial uniformity of heat conduction through the metallic collector block and uniformity of heat transfer from the collector block to the fluid coolant.

Most conventional collectors for electron beam tubes are constructed so as to provide a high volume of fluid coolant through the collector with a small rise in the coolant temperature and without regard to other factors controlling hydraulic turbulence. This practice is said to be justified by the fact that when there is only a small rise in the fluid coolant temperature, the fluid coolant may be admitted to the collector at a higher temperature; as a consequence of the higher inlet temperature, a smaller heat transfer unit may be utilized to cool the fluid coolant after it has left the collector. However, if the collector can be designed to use a greater differential between inlet and outlet temperatures and simultaneously allows a high inlet temperature and low flow rate, a very efiicient collector will result. It is accordingly another object of the present invention to provide a collector which is relatively small in physical dimensions, which operates at a relatively great disparity between the inlet and outlet temperatures, which possesses a low volume flow, and which permits high inlet temperatures.

Another important consideration in the design of a collector electrode for an electron beam tube utilizing a re-entrant magnetic circuit is the outside diameter of the collector. Most conventional electron beam tubes re quire a magnetic circuit to radially confine the electron beam. With tubes using a re-cntrant magnetic circuit,

the diameter of the collector has a twofold effect on the size and efficiency of the magnetic circuit. First, the magnetic field strength obtained from a coil depends di rectly on its mean diameter which is determined in part by the diameter of the collector which the coil must surround. Second, the total gap field of the magnetic circuit depends on the area of the magnetic pole piece, which is again a function of the collector diameter where a pole piece forms an integral part of the tube assembly. It is therefore another important object of the present invention to provide a collector electrode having a small diameter in roportion to the amount of power which it dissipates.

During operation of an electron tube equipped with a fluid cooled collector, the coolant flow rate in terms of volume should be as small as possible With a reasonable pressure drop in the coolant system. It is also desirable that the fluid coolant passages be of simple and uncomplicated configuration so as to eliminate difliculties attendant to fabrication of the collector. It is therefore a still further object of the present invention to provide a collector which utilizes simply formed longitudinally extending parallel passageways for passage of the fluid coolant.

The invention possesses other objects and features of value, some of which, with the foregoing, will be apparent from the following description and the drawings. it is to be understood, however, that the invention is not limited to the embodiment illustrated and described, as the invention may be embodied in various forms within the scope of the appended claims.

Broadly considered, the collector construction of the invention comprises an elongated metallic block, preferably of copper and having an interior chamber within which the electron beam is adapted to impinge. Around its exterior periphery the collector block is provided with a plurality of longitudinally extending passageways constituted by circumferentially spaced radially extending fins formed by milling grooves in the outer peripheral surface of the collector block. The fins lie parallel to each other and parallel to the axis of the collector. At one end the collector block is provided with an annular manifold plate or block having a chamber therein and a plurality of radially extending passageways forming a set thereof communicating the manifold chamber with specific passageways or grooves formed in the circumferential periphery of the collector, groups of these latter being arranged in sets, each set comprising a plurality of longitudinally extending passageways, one of which is designated an inlet passageway and another an outlet passageway with the radial passageways in the manifold plate connecting the inlet passageways of each set. Other longitudinally extending passageways formed in the manifold plate communicate with the outlet passageways of the circumferentially spaced collector block passageways. A fluid coolant admitted to the chamber flows from the manifold chamber into the longitudinally extending parallel inlet passageways. After coursing in parallel the length of the collector block through the inlet passageways, the fluid coolant flows into the next adjacent pas sageway of the set which channels it in the opposite direction to again traverse the length of the collector block, after which it flows in opposite directions in the next two passageways constituting the set, from the last one of which, designated an outlet passageway, the coolant again flows through the manifold plate and exits from the collector. It will thus be seen that a multiplicity of sets of coolant passageways are provided, with the passageways in each set connected in series and with the sets of passageways connected in parallel. This interconnection of the collector passageways with the manifold plate to permit parallel interconnection has the beneficial effect of causing the heat to distribute evenly throughout the collector block, and also effects a uniform heat transfer from the metallic wall of the collector to the fluid coolant. To channel the fluid coolant serially through the proper passageways, the exterior peripheral cylindrical surface of the collector block is sealed into a cylindrical stainless steel sleeve which fits in a fluid-tight shrink-fit closely about the outer peripheral edges of the fins or lands which form the collector passageways.

Because it is desirable that electrons that enter the hollow collector be trapped therein, and that secondary electrons liberated by high velocity primary electrons also be trapped within the collector, the open or input end of the hollow collector block is provided with a secondary electron suppressor shield or baflle plate to prevent egress of electrons from the collector and impingement on the body of the electron tube. Means are also provided electrically insulating the conductive collector block from the adjacent electron tube body.

Referring to the drawings:

FIGURE 1 is a vertical cross-sectional view disclosing the interior construction of the collector. Portions of the structure are in elevation to disclose the interconnection of the collector block coolant passageways.

FIGURE 2 is a horizontal cross-sectional view taken in the plane indicated by the line 2--2 in FIGURE 1. The view illustrates the relationship of groove depth, fin thickness and wall thickness of the collector.

FIGURE 3 is a horizontal cross-sectional view taken in the plane indicated by the line 33 in FIGURE 1. The view illustrates the relationship between adjacent parallel sets of passageways extending longitudinally of the collector block.

FIGURE 4 is a horizontal sectional view taken in the plane indicated by the line 4-4 in FIGURE 1. The view illustrates the radially and longitudinally extending slots or passageways formed in the manifold plate for interconnecting respectively, the inlet and outlet passageways of the collector.

FIGURE 5 is a horizontal cross-sectional view taken through the manifold plate, the section being taken in the plane indicated by the line 55 of FIGURE 4.

All of the figures are drawn approximately actual size.

In the design ofan-eflicient collector for an electron beam tube, one of the first considerations is the power density distribution of the beam after it has entered the collector. Conveniently, the power density distribution of the beam within the collector is proportional to the power density distribution of the electron beam before it enters the collector. This enables close approximation of the power density of impingement of the electron beam within the collector, the inside diameter and configuration of the collector surface against which the electrons impinge being selected with due consideration to the impinging power density and the total power required to be dissipated. Ideally, the inner surfaces of the collector block will possess a curved configuration providing a constant impinging power density over an appreciable length of collector. Such a surface is extremely difficult to ma chine, and is costly in time and money. It is possible and practicable, however, to approximate such a curved surface by formation of a part of the collector block in a single or plurality of axially aligned portions having their interior surfaces conically tapered toward the axis of the collector.

With the inside diameter of the collector block a known factor, and with the thermal conductivity of copper and the power to be dissipated also known, it is possible to determine the length of the collector which will dissipate with a reliable margin of safety the heat generated in the collector by impingement of the electron beam notwithstanding the fact that the interior surfaces of the collector block only approximate a configuration which would provide a constant impinging power density.

Since it is desired to transfer the heat so generated into a suitable fluid coolant, it is important that the temperature of the copper remain below the critical temperature at which boiling of the fluid coolant occurs, it being noted that this critical temperature is dependent on several facors such as coolant used, pressure and velocity. The heat transfer through the collector block and into the fluid coolant is proportional to the temperature of the copper less the temperature of the fluid coolant. Heat transfer is also proportional to the velocity of the fluid coolant flowing through the passageways, and is inversely proportional to the hydraulic diameter of the passageways themselves.

The velocity and hydraulic diameter of the passageways is important because these factors, with pressure, control the total amount of fluid coolant required in the system and determine also whether the flow of the fluid coolant is laminar or turbulent. Turbulent flow and not laminar flow is preferred because heat transfer is more efiicient with turbulent flow. Since the amount of power which must be dissipated per unit area of collector surface is known, and since the flow rate in volume of fluid coolant for a given system is more or less discretionary, it is desirable that heat transfer efficiency of the collector be optimized for a reasonably small volume of fluid coolant by increasing the surface area over which the fluid coolant will flow.

The collector of this invention therefore comprises a longitudinally extending hollow metallic body symmetrical about a longitudinal axis, and having a first hollow cylindrical body portion 2, having a cylindrical interior surface 3 formed therein, and a multiplicity of longitudinally extending collector block passageways 4 formed in its outer periphery at circumferentially equally spaced intervals. The passageways 4 are defined by longitudinal radially extending fins 7, left projecting from the cylindrical surface of the collector block by the milling operation which forms the passageway 4. The fins may of course be formed by a hobbing operation or as extrusions. At one end of the tubular collector block portion 2, the end portions of alternate fins 7 are milled away as shown at 8 in FIGURE 1, to provide a connection at this end of the collector of two adjacent passageways forming a pair. From FIGURE 1 it will be seen that adjacent pairs are circumferentially spaced about the collector block and that the intermediate fin 7 between the adjacent pairs of connected passageways prevents flow of fluid coolant from one pair to the other at this end of the collector. Instead of being milled away a depression may be formed in flange 23 opposite the end of a fin to provide intercommunication between two adjacent passageways forming a pair.

At the other end, the collector block 2 is closed by a terminal or end block collector portion 13, having conically tapered interior walls 14 defining a hollow chamber 16 communicating at one end with the collector portion 2 and closed at its opposite end by wall 17. The exterior cylindrical surface of the collector end block portion 13 is milled to provide the same number and spacing of fins as in collector block portion 2. The collector blocks 2 and 13 are brazed at the jointure line 18 so that the fins align themselves to provide continuous passageways over the entire length of the collector. At the end of collector block 13 adjacent end Wall 17 thereof, every fifth fin is milled away as indicated at 19 in FIG- URE 1 so that also at this end of the collector two adjacent passageways 4 are serially interconnected to form a pair, one passageway of this pair constituting one of the passageways of the pair thereof discussed with respect to the other end of the collector. In this way four adjacent passageways are serially interconnected to form one set of four passageways. As shown in FIGURE 1, the outer passageways of each set form inlet and outlet passageways, with the inlet passageway of each set being next adjacent the outlet passageway of the next adjacent set of passageways. For increased efficiency and reduction of the pressure drop through the system, the inlet and outlet passageways are charnfered at their ends adjacent the collector end wall as shown at 29. The inlet passageways may collectively be considered a set of inlet passageways and the outlet passageways may collectively be considered a set of outlet passageways.

Thus, in the embodiment illustrated, at each twentyfour degree interval about the collector, a fin extends the entire length of the collector, while of the three fins therebetween, the two outside fins are milled away at one end adjacent the input end of the collector while the remaining fin between these two is milled away at the opposite or closed end of the collector. Two adjacent full length fins thus define between them a set of passageways.

In order that fluid coolant may progress through the passageways, the entire collector block is enclosed within a stainless steel sleeve 21 which forms a shrink-fit about the outer ends of the fins. At its input end, the collector is provided with a cylindrical member 22, having a radially extending flange 23 brazed within the end of the sleeve. The flange also abuts the end of the tubular portion 2, and is brazed thereto in a fluid-tight manner. At its opposite end, the tubular member 22 is provided with a truncated hollow conical secondary electron suppression shield or baflle plate 24 having its large base brazed to one end of the tubular member 22, and having an aperture 26 at its apex end through which the beam enters the collector body. As shown in FIGURE 1, the aperture in the apex end of the suppressor shield is materially smaller than the inner diameter of either the tubular member 22 or the collector portion 2. The aperture is preferably proportioned to closely surround the beam after it passes the last interaction gap and before it spreads materially, which eflect occurs after the beam has passed into the collector where the electrons spread outwardly and impinge upon the inner surface of the collector as indicated by the dash lines 27. As often happens, the primary electrons entering the collector will release secondary electrons from the walls of the collector. With the present design of the secondary electron suppressor plate or shield, these secondary electrons impinge on the shiled plate and do not impinge upon the body of the electron tube as would be the case in the absence of the shield plate. Since the collector electrode is electrically insulated from the radio frequency body structure 28 of the electron tube by the sealing means 29 illustrated in FIGURE 1, electrons which impinge upon the suppressor shield have no effect on either the temperature or the body current of the electron tube, the value of the latter of which is an excellent indication of the percentage beam current being intercepted by the body of the electron tube.

To admit a fluid coolant into the collector passageways, an annular manifold plate 31 is superposed over and brazed to the closed end wall 17 of the collector block 13 within the cylindrical sleeve 21. The manifold plate is brazed about its outer periphery within the sleeve, and is provided with a central aperture 32, rabbeted as shown, to receive the inner end of an inlet conduit 33. Adjacent the opposite face of the manifold plate the central aperture is increased in diameter and communicates with a manifold chamber 34, having a plurality of radially extending slots 36 milled in the manifold plate between the inner periphery of the centrally disposed manifold chamber and the outer perpihery of the manifold plate. As shown best in FIG- URE 4, there are conveniently fifteen such passageways connecting the manifold chamber with the exterior periphery of the manifold plate.

The passageways 36 are circumferentially equally spaced about the manifold plate and constitute inlet passages connected to selected ones of the passageways 4 constituting inlet passageways in each set of four passageways and which extend longitudinally along the periphery of the collector block as discussed above. As shown in FIGURES l and 5, the radially extending grooves 36 do not extend longitudinally through the entire depth of the plate 31, but rather extend only to a depth correponding to the depth of the manifold chamber 34.

Also milled into the manifold plate are a multiplicity of slots or passageways 37 which do extend longitudinally through the manifold plate. These passageways, as shown best in FIGURES 1, 4 and 5, extend through the thickness of the manifold plate and extend radially for a distance, but not suificiently to communicate the inner and outer peripheries of the plate. In the structure illustrated, there are preferably fifteen such passageways 37, each connecting a selected one of the outlet passageways 4 formed in the collector block. It will thus be seen that by orienting the manifold plate so that one of the inlet slots 36 registers with a selected one of the inlet passages 4 in the collector block, fluid coolant will be caused to flow in parallel through the sets of passageways, and serially through adjacent passageways 4 in each set. This occurs by virtue of the fact that the inlet slots 36 are spaced circumferentially 24 apart about the manifold plate 31, and the passageways 4 in the collector block are correspondingly spaced.

As viewed in FIGURE 1, therefore, the fluid coolant will flow from the chamber 34 radially outwardly through the radially extending slots 36 into the longitudinally extending inlet passageways 4 which are registered with the associated slots 36. Fluid coolant will then flow in the same direction through all the inlet passageways 4 longitudinally of the collector block as shovm best by the arrows in FIGURE 1.

As the fluid coolant comes to the end of the fin at the input end of the collector which has been milled away as at 8, the fluid coolant is channeled around the fin 7 by the flange 23 and progresses in the opposite direction through the next adjacent passageway 4, until it reaches the opposite end of the collector block and the area 19 produced by milling away the end of another of the fins 7, at this end constituting every fourth one. The fluid coolant flows around the end of the fin, channeled by the flat surfaces 38 of the manifold plate, and flows the length of the collector block again, and is again directed or channeled into the next adjacent passageway by another area 8 formed as before by milling away the end of the fin.

In its fourth and last passage over the length of the collector block, the fluid coolant exits from the fourth or outlet passageway into one of the passageways 37 which communicates with an annular chamber 39 defined between plate 31, sleeve 21 and a closure plate 41, the chamber 39 functioning to combine the fluid coolant from all of the outlet passageways 37 and discharge the fluid coolant into the outlet conduit 42.

It will thus be seen that the longitudinally extending passageways 4 surrounding the collector block are arranged in a plurality of circumferentially spaced sets, there being 15 such sets spaced 24 apart about the outer periphery of the collector block in the embodiment illustrated. Each set of passageways is connected in parallel with the remaining sets through the medium of the collector manifold chamber 34 and associated inlet passageways 36. Each set is also connected in parallel with the remaining sets by outlet passageways 37 connected with each associated set and combining the outflow from each set into a common chamber 39.

Within each set, there are four passageways, two of the passageways carrying the fluid coolant in one direction longitudinally of the collector, and the remaining two passageways of the set carrying the fluid in the opposite direction. As shown by the arrows in FIGURE 1, within each set the direction of flow reverses in adjacent passageways. In this manner fluid coolant admitted to each set of passageways at the closed end of the collector block egresses from that particular set at the same end of the collector block. This facilitates connection of the collector to a coolant system.

Another advantage of this arrangement is that it places the outlet passageway for each set next adjacent the inlet passageway for the next set. In this manner, the coldest fluid coolant entering the system is placed next adjacent the outlet passage carrying the hottest fluid coolant. This arrangement ensures that as the hottest portion of the coolant egresses from the collector cooling system, the fins which define this outlet passageway will remain at a temperature below the critical temperature previously defined. The arrangement thus minimizes non-uniformity in the distribution of heat through the collector block.

In the manufacture of the electron tube collectors which utilize thick billets of copper to form collector block portions, it has been found that the copper blocks are often defective in that in the process of manufacture of the blocks, pipes or longitudinally extending passageways are formed in the copper which permit the passage of air. In a construction such as that illustrated, where a relatively short block 13 is provided with a conical depression 16 closed by a relatively thin wall 17, such pipes may extend from the interior of the collector to an exterior surface thereof. In the collector illustrated, in order to preclude the pipes from forming a passageway for air between the exterior and the interior of the collector, the end of the collector block 13 next adjacent the manifold plate is provided with a copper seal plate 44 fabricated so that its grain structure lies in a direction perpendicular to the grain structure of the block 13. The plate is preferably brazed in a recess formed in the end of the collector block 13 and possesses a thickness suflicient to provide a projecting portion as shown useful as a guide to center the manifold plate over the end of collector block.

It will thus be seen that for eflicient operation of the collector, it is important that the cylindrical sleeve 21 which surrounds the passageways 4 and fins 7 be united to the ends of the fins in a fluid-tight manner to confine the flow of fluid coolant in the desired passageways. To accomplish this, the fins 7 and passageways 4 are preferably silver plated, and so is the interior surface 43 of the sleeve 21. The sleeve is then assembled onto the collector block by shrink-fitting the sleeve 21 thereon. The entire assembly is then passed through a brazing furnace to effect brazing of the sleeve to flange 23 and plate 41. In this operation the silver plate and the copper of the fins 7 form a eutectic which brazes the outer edge of each fin 7 to the inner surface 43 of the sleeve 21 in a watertight manner.

In operation, it has been found that a collector fab ricated according to this invention is capable of efliciently dissipating at least 70 kw. of power. In the structure shown, the heat transfer capacity is designed to be about one kilowatt per square inch of collector surface. It has been found that this power dissipation is conveniently etfected with fins that are A; of an inch high, spaced at equal intervals about the outer periphery of the collector block and arranged in parallel sets as discussed above. The spacing of the grooves and fins at whole number degrees about the outerperiphery of the collector block is important in that it greatly facilitates milling of the collector block's. When fins are spaced whole number degrees apart, the indexing guide or head of the milling machine on which the collector is milled may be set directly without consideration of fractions of degrees. This greatly increases uniformity of fin dimension, facilitates fabrica tion, and lessens the time spent in milling the collector, with an attendant saving in cost.

I claim:

1. In an electron tube, a fluid-cooled electrode element comprising a hollow body having a cylindrical side wall disposed about a longitudinal axis, a multiplicity of elongated circumferentially spaced parallel projections on the cylindrical side wall defining axially extending channels through which a fluid coolant may flow, elected ones of said circumferentially spaced projections defining noncommunicating sets of said channels, two adjacent of said selected projections having disposed therebetween three intermediate projections arranged to provide two pair of adjacent parallel channels serially intercommunicated with each other, jacket means surrounding said body to enclose said channels, and means connecting the separate sets of channels in parallel connection with a source of fluid coolant.

2. The combination according to claim 1, in which one end of one of said three intermediate projections adjacent one end of the body is axially spaced from the associated ends of the adjacent selected ones of said projections.

3. The combination according to claim 1, in which one channel in each set constitutes an inlet channel and another channel in each set constitutes an outlet channel, the inlet channel of each set being disposed on one side of each respective selected projection and being circumferentially spaced next adjacent the outlet channel of the next adjacent set of channels which is located on the other side of the selected projection.

4. A fluid-cooled electrode for an electron tube comprising a hollow body having a cylindrical side wall disposed about a longitudinal axis and an end wall closing one end of the hollow body, a multiplicity of elongated parallel passageways extending axially through the side wall adjacent the outer cylindrical periphery thereof and through which a fluid coolant may flow, said passageways being arranged in at least two separate sets of passageways, each set having four of said passageways including an inlet and an outlet passageway, and means adjacent one end of the hollow body connecting in parallel the inlet passageways of the separate sets and connecting in parallel the outlet passageways of the separate sets.

References Cited by the Examiner UNITED STATES PATENTS 2,871,397 1/1959 Preist et al. 3155.46 3,098,165 7/1963 Zitelli 3132l DAVID J. CALVIN, Primary Examiner.

Claims (1)

1. IN AN ELECTRON TUBE, A FLUID-COOLED ELECTRODE ELEMENT COMPRISING A HOLLOW BODY HAVING A CYLINDRICAL SIDE WALL DISPOSED ABOUT A LONGITUDINAL AXIS, A MULTIPLICITY OF ELONGATED CIRCUMFERENTIALLY SPACED PARALLEL PROJECTIONS ON THE CYLINDRICAL SIDE WALL DEFINING AXIALLY EXTENDING CHANNELS THROUGH WHICH A FLUID COOLANT MAY FLOW, SELECTED ONES OF SAID CIRCUMFERENTIALLY SPACED PROJECTIONS DEFINING NONCOMMUNICATING SETS OF SAID CHANNELS, TWO ADJACENT OF SAID SELECTED PROJECTIONS HAVING DISPOSED THEREBETWEEN THREE INTERMEDIATE PROJECTIONS ARRANGED TO PROVIDE TWO PAIR OF ADJACENT PARALLEL CHANNELS SERIALLY INTERCOMMUNICATED WITH EACH OTHER, JACKET MEANS SURROUNDING SAID BODY TO ENCLOSE SAID CHANNELS, AND MEANS CONNECTING THE SEPARATE SETS OF CHANNELS IN PARALLEL CONNECTION WITH A SOURCE OF FLUID COOLANT.

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