US3526798A

US3526798A - X-ray shield structure for liquid cooled electron beam collectors and tubes using same

Info

Publication number: US3526798A
Application number: US730509A
Authority: US
Inventors: Lars H Sandstrom
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1968-05-20
Filing date: 1968-05-20
Publication date: 1970-09-01
Anticipated expiration: 1987-09-01

Description

p 1970 L. H. SANDSTROM 3, 8

X-RAY SHIELD STRUCTURE FOR LIQUID COOLED ELECTRON BEAM CQLLECTQRS AND TUBES USING SAME Filed May 20, 1968 INVENTOR. LARS H.5ANDSTROM @M l; Z

ATTORNEY United States Patent O 3,526,798 X-RAY SHIELD STRUCTURE FOR LIQUID COOLED ELECTRON BEAM COLLECTORS AND TUBES USING SAME Lars H. Sandstrom, Cupertino, Califi, assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed May 20, 1968, Ser. No. 730,509 Int. Cl. G21f 7/00; H01j 19/36 U.S. Cl. 313-22 1 8 Claims ABSTRACT OF THE DISCLOSURE An electron beam tube is disclosed. The tube includes an electron gun for forming and projecting a beam of electrons over an elongated beam path to a beam collector structure disposed at the terminal end of the beam. The beam collector structure includes a chamber having an opening at one end for passage of the beam into the chamber and which is closed on the other end to collect that portion of the beam which passes through the chamber to the closed end. An array of liquid coolant channels are provided along the side Walls of the beam collector chamber in heat exchanging relation with the chamber walls for cooling same. A liquid coolant manifold structure is disposed over the closed end of the collector for distributing to and collecting liquid coolant from the array of coolant passageways. The liquid coolant manifold includes first and second axially spaced chambers with a pair of pipes communicating with the first chamber and a pair of pipes interconnecting the first and second chamber. An X-ray shield as of lead is provided closely surrounding the beam collector chamber and the liquid coolant channels, such shield also covering over the end of the coolant manifold and including a portion disposed intermediate the first and second axially spaced chambers thereof. The coolant pipes connected into the first chamber and interconnecting the first and second chambers of the manifold are axially offset with respect to each other such that the X-ray shield portion disposed between the two chambers blocks any line of sight passageway for X-rays from the beam collector chamber through the two sets of pipes. In the preferred embodiment, a pair of elbow-shaped X- ray shield members are provided covering elbow pipe fittings connecting into the first manifold chamber.

DESCRIPTION OF THE PRIOR ART Heretofore, electron beam tubes have included collector structures having an X-ray shield for preventing escape of X-rays from the collector. Typical of such prior art X-ray shields is that disclosed in U.S. Pat. 3,374,390 issued Mar. 19, 1968 and assigned to the same assignee as the present invention. In that prior tube structure, the beam collector chamber is surrounded by an elongated cup-shaped X-ray shield, as of lead. The bottom of the cup-shaped lead shield member is apertured to accommodate passage of a pair of pipes for conducting liquid coolant to and from a coolant manifold structure afiixed over the end of the beam collector chamber.

The problem with such an X-ray shield structure is that X-rays, generated within the beam collector chamber, can pass out of the X-ray shield by passing through the apertures in the shield which were provided to accommodate Patented Sept. 1, 1970 the liquid coolant pipes. When the electron tubes are operating at relatively high beam voltages and high power levels, the X-ray radiation escaping from the beam collector through the apertures provided for the coolant pipes becomes substantial and constitutes a radiation hazard to operating personnel. Previous attempts to solve the escape of radiation from the aforementioned tube structure have included the provision of additional X-ray shielding members, such as sheets of lead, wrapped around and over the coolant pipes leading to and from the beam collector structure. While such additional shielding members can substantially reduce the dangerous X-ray radiation such members become excessively large and bulky because they are disposed at some distance from the collector structure.

Therefore, a need exists for an improved X-ray shielding structure that may be incorporated as an integral unit into the beam collector structure, thereby reducing the size and weight of the required X-Iay shielding members.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved X-ray shield for liquid cooled electron beam collectors and tubes using same.

One feature of the present invention is the provision, in a liquid cooled electron beam collector structure, of separating the liquid coolant manifold structure into a pair of axially spaced coolant chambers disposed at the end of the beam collector and offsetting the axial centerlines of one pair of coolant pipes, communicating With the outer chamber, with respect to the axial centerlines of a second pair of coolant pipes communicating through the axial space between the axially spaced chambers, and disposing an X-ray shield structure with a first portion in the space betweent he two axially spaced chambers and a second portion over the outer end of the manifold to block a line of sight path for the X-rays from the inside of the beam collector to the outside thereof through the liquid coolant manifold structure.

Another feature of the present invention is the same as the preceding feature wherein the X-ray shield structure disposed between the two axially spaced chambers is apertured to accommodate the pipes communicating therebetween and is split axially and transversely thereof along a line intersecting with the apertured portion to facilitate placement of the X-ray shield around the liquid passageways.

Another feature of the present invention is the same as any one or more of the preceding features wherein the end portion of the X-ray shield structure, which covers over the liquid coolant manifold, includes one or more apertures to accommodate the liquid passageways communicating with the manifold and such end covering shield structure being axially split along a transverse line intersecting with the apertured portion of the structure to facilitate placement of the X-ray shield structure around the liquid passageways.

Another feature of the present invention is the same as any one or more of the preceding features wherein the liquid passageways communicating with the fluid manifold structure include a pair of elbow pipe fittings and a pair of elbow-shaped X-ray shield structures being fitted over said elbow pipe fittings to further reduce the possibility of stray X-ray radiation leaking through the X-ray shield structure.

Another feature of the present invention is the same as any one or more of the preceding features wherein the outer end manifold chamber includes a partitioning wall partitioning the chamber into two lesser chambers for passage of liquid coolant in opposite directions through the partitioned chamber.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal view, partly in section, of an electron beam tube incorporating features of the present invention,

FIG. 2 is an enlarged longitudinal sectional view of a portion of the structure of FIG. 1 delineated by line 22,

FIG. 3 is a schematic line diagram of a transverse sectional view of the structure of FIG. 2 taken along lines 3-6 in the direction of the arrows, and

FIG. 4 is a sectional view of a portion of the structure of FIG. 3 taken along the lines 4-4 in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown an electron beam tube 1 incorporating features of the present invention. The tube 1 includes an electron gun 2 for forming and projecting a beam of electrons 3 over an elongated beam path to a beam collector structure 4 disposed at the terminal end of the beam path. An electromagnetic interaction circuit 5 is disposed intermediate the gun 2 and collector 4 and along the beam path 3 for electromagnetic interaction with the beam to produce an output microwave signal.

Input microwave signals to be amplified are applied to the upstream end of the interaction circuit 5 via an input coaxial line 6. Output microwave energy is extracted from the downstream end of the microwave circuit 5 via output waveguide 7 which is sealed in a vacuum tight manner by means of a wave permeable dielectric window member 8. A beam focus solenoid 9 coaxially surrounds the tube 1 for producing an axially directed beam focus magnetic field over the beam path for confining the beam to a desired beam diameter throughout the interaction circuit 5. Inside the collector structure 4 the beam spreads due to space charge debunching forces and is collected more or less uniformly over the interior surfaces of the collector, more fully described below with regard to FIGS. 2-4. The aforedescribed tube structure is essentially similar to that described and claimed in the aforecited US. Pat. 3,374,390.

Referring now to FIGS. 2 and 3, there is shown the beam collector structure 4 incorporating features of the present invention. More specifically, the collector structure 4 includes a hollow conductive chamber 11 as of copper which is open at one end 12 for passage of the electron beam 3 into the collector chamber 11. The other end of the chamber 11 is closed by a conical end wall 13- for collecting that portion of the beam which passes through the beam collector chamber 11 to the wall 13. The external side surfaces of the beam collector chamber 11 include an array of closely spaced longitudinally directed fins 14 as of copper. The spaces between adjacent fins 14 constitute liquid coolant passageways which extend substantially the full length of the collector chamber 11. A radial array of fins 14 extend radially from the center of the end wall 13 to the outer diameter of the chamber. The radially directed fins 14 define liquid coolant passageways therebetween on the outside of the conical end wall 13. The radial passageways communicate only with alternate ones of the passageways along the side walls of the chamber.

A cylindrical baffle 15, as of stainless steel, surrounds and is aifixed over the outer side edges of the vanes 14 1 to define the outer side wall of the coolant passageways. The bafile 15 is sealed at its upstream end to a shoulder portion 16 of the beam collector structure 4. A hollow toroidal shaped coolant collecting chamber 17 is defined by the spaces between the upstream ends of the fins 14 and the inside surface of the shoulder 16. A conically shaped bafile plate 18, as of stainless steel, is affixedover the conical array of coolant fins 14 and passageways provided of slots and thence along the sides of the collector to the toroidal collecting chamber 17 from whence the coolant passes in a reverse direction along the outside of the collector chamber 11 in the adjacent set of slots through the slotted peripheral margins of the bafiie 18 into an annular collecting chamber .20 of a coolant distribution manifold structure 21 disposed over the outer end of the collector chamber 11.

In the coolant distribution manifold structure 21., the.

structure is divided into a pair of axially spaced chambers, i.e., annular collection chamber 20 and an outer axially spaced shallow cylindrical chamber 22.

Chambers

20 and 22 are defined by the regions of space between

transverse disc structures

23, 24, 25 and the outer surface of the conical baffie 18. More specifically, end chamber 22 is defined by the region of space between the end disc-shaped wall 23 and transverse disc 24, whereas collector chamber 20* is defined by the space between the conical bafiie 1'8 and the disc 25. The side walls of the

chambers

20 and 22, respectively, are defined lby cylindrical sections of the cylindrical bafile 15. A pair of

cylindrical coolant pipes

26 and 27 interconnect chambers 22 i with the collection chamber 20 and with the conical array of radially directed coolant channels on the end of the collector wall 13, respectively. The

coolant pipes

26 and 27 pass through the axial space 28 between the collec-v tion chamber 20 and the outer chamber 22.

An apertured disc-shaped X-ray shield member 29, as

of "/2 inch thick lead, is disposed in the region 28 between the collection chamber 20 and the end chamber 22. The lead shield member 29 includes a pair of

apertures

31 and 32, respectively (see FIG. 3) to accommodate the

coolant pipes

27 and 26, respectively. The,

X-ray shield disc 29 is axially split along a transverse line 33 which intersects both apertures 31- land 32 to divide the disc-shaped shield member 29 into two parts to facilitate placement of the shield 29 in the space 28,- since by splitting the member 29 it may be slipped into the region 28 from diametrically opposed sides as in dicated by the arrows 34 in FIG. 3. A similarly discshaped lead shielding member 35 is affixed .over the outer end of the coolant distribution manifold 21 and is similarly apertured by a pair of

holes

36 and 37 to a accommodate a pair of elbow pipe fittings 38 which are in fluid communication with the end chamber 22 via a pair of ports 39 provided in the end wall 23. The ports 39,

elbow fittings 38, and the corresponding apertures 36 i and 37 in the lead shielding member 35 are axially oifset.

with respect to the axes of the

coolant pipes

26 and 27 which pass through the first X-ray shielding disc 29. In

this manner, X-rays generated within the collector chamber 11 and tending to pass in straight line out through i the end of the collector structure are blocked due to the lack of a straight line passageway'through bothof the first and second pairs of holes in the X-ray shields 31 and 32 and 36 and 37, respectively. The end X-ray shielding disc 35 is axially split by means of a transverse joint 41 which intersects both

apertures

36 and 37 such that the end shield 35 may he slipped into position around the elbows 38 from diametrically opposed sides as in dicated by arrows 42.

One elbow-shaped lead shield member 43 is aflixed over the pair of elbow fittings 38 to further block the escape of X-rays that may possibly find an off axis straight line path through aperture 32 in shield member 29 and through either

aperture

36 or 37 in shield member 35.

The transverse joints 33 and 41 in X-ray

shielding disc members

29 and 35 include an axially offset region as shown in FIG. 4, such that X-rays cannot pass axially through the joints.

The end chamber 22 in the coolant distribution manifold includes an internal partition 44 which has a right angle bend as shown in FIG. 3 to separate the chamber 22 into two separate portions to accommodate the inflow of cold coolant and the outflow of warm exhaust coolant. The direction of coolant flow is indicated by the arrows of FIG. 3 and, briefly, input coolant flows through input elbow pipe fitting 38 through port 39 thence through the centrally disposed coolant pipe 26 into the center of the conical array of cooling fins provided on the end of the collector. The coolant then flows radially across the end of the collector and down the sides returning through adjacent channels in the sides and into the collector chamber 20. From the collector chamber 20, the coolant flows through pipe 27 into the exhaust side of the partitioned chamber 22 and thence through the exhaust elbow fitting 38 which communicates through the shield aperture 36 with the chamber 22.

A cylindrical X-ray shielding member 45 surrounds the sides of the collector chamber 11 and the distribution manifold 22 to prevent the escape of X-rays out the sides of the collector. A magnetic shielding cup-shaped member 46 as of iron surrounds the X-ray shielding members I 45 and 35, respectively. In certain tube embodiments, it

is desirable to have the collector 4 operating at a potential independent of the potential applied to the body of the tube such that body current can be monitored independently of the current collected by the collector 4. In such a case, conventional insulator structures, not shown, support the collector chamber 11 from the body of the tube. However, the outer

X-ray shield structure

35, 45, and 43 and the magnetic shield member 46 are typically operated at body potential and, therefore, an insulator must be provided between the external

X-ray shielding members

35, 45 and 43 and those internal portions of the collector structure to be operated at the independent potential. Accordingly, a thin cup-shaped insulator 47 as of sheet Teflon, is aflixed over the end of the coolant dis tribution manifold structure 21 and an elbow-shaped insulator 48 is disposed between the elbow X-ray shielding members 43 and the elbow pipe fittings 38. Insulative hoses, as of rubber, are then utilized for connecting the elbow fittings 38 to suitable pipes for piping a liquid coolant to and from the collector structure 4.

The advantage of the X-ray shield structure of the present invention is that the pair of axially spaced discshaped

X-ray shielding members

29 and 35, having offset apertures therein to accommodate the flow of coolant through the coolant manifold structure, effectively blocks all X-ray emission from the collector which tends to pass out the end thereof. The cylindrical X-ray shielding member 45, which surrounds the side of the collector chamber 11, and the sides of the distribution manifold 21 effectively blocks all X-ray radiation which tends to pass out through the sides of the collector 4. Thus, an efficient and compact X-ray shield structure for beam collector structures is obtained.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an electron tube apparatus, means for forming and projecting a beam of electrons over an elongated beam path, means at the terminal end of the beam path for collecting and dissipating energy of the beam, said beam collecting means including a chamber having an opening in one end for passage of the beam into said chamber and being closed on the other end to collect that portion of the beam passing through said chamber to the closed end thereof, means forming liquid coolant passageways for passing a liquid coolant along the side walls of said beam collector chamber in heat exchanging relation with the walls of said chamber for cooling same, means forming a liquid coolant manifold structure disposed over the closed end of said beam collector chamber for distributing and collecting the liquid coolant through said liquid coolant passageways, means form ing an X-ray shield structure disposed closely surrounding said collector chamber and liquid coolant passageways and having a portion covering the end of said beam collector chamber and said liquid coolant manifold, the improvement wherein, said liquid coolant manifold structure comprises first and second axially spaced chambers, said first chamber having a pair of fluid passageways communicating therewith through said end covering portion of said X-ray shield, means forming a second pair of liquid passageways communicating between said first and second axially spaced chambers of said manifold, said first and second pairs of fluid passageways being disposed in axially offset relation with respect to each other such as to block an axially directed straight line passageway through both of said first and second pairs of passageways, and an X-ray shield structure disposed in the axial space between said first and second manifold chambers for blocking passage of X-rays except through said liquid passageways communicating between said axially spaced chambers.

2. The apparatus of claim 1 wherein said X-ray shield structure disposed in the space between said first and second manifold chambers comprises a structure apertured to accommodate said pair of fluid passageways communicating between said first and second manifold chambers, and said apertured structure being axially split along a transverse line intersecting said apertured portion of said structure to facilitate placement of said X-ray shield structure around said liquid passageways.

3. The apparatus of claim 2 wherein said apertured X-ray shield structure includes two apertures, and said structure is axially split along the transverse line intersecting both of said apertures in said structure.

4. The apparatus of claim 2 wherein said apertured X-ray shield structure is disc-shaped.

5. The apparatus of claim 1 wherein said end portion of said X-ray shield structure which covers over said liquid coolant manifold includes an apertured structure to accommodate said liquid passageways communicating with said liquid manifold chamber through said end portion of said X-ray shield structure, said end covering shield portion being axially split along a transverse line intersecting with said apertured portion of said end portion to facilitate placement of said X-ray shield structure around said liquid passageways.

6. The apparatus of claim 5 wherein said end covering X-ray shield portion includes two apertures, and said portion is axially split along a transverse line intersecting both of said apertures in said end portion.

7. The apparatus of claim 5 wherein said liquid passageways communicating with said first chamber are defined by a pair of elbow pipe fittings and a pair of elbowshaped X-ray shield structures being fitted over said elbow pipe fittings.

7 8 8. The apparatus of claim 1 wherein said first mani- 3,122,669 2/1964 Nelson 313*24 fold chamber includes a partitioning wall partitioning 3,305,742 2/1967 McCune 313--21 X said chamber into two lesser chambers for passage of 3,359,451 12/1967 Zitelli et a1 31330 X liquid coolant in opposite directions through said parti i d h b 5 JAMES W. LAWRENCE, Primary Examiner References Cited E. R. LA ROCHE, Assistant Examiner UNITED STATES PATENTS US. Cl. X.R.

3,098,165 7/1963 Zitelli 313-32 X 313-32, 35; 315-5.38;250-108 3,104,338 9/1963 Symons 3l55.38 X 10