Patent Number: 
Section: description

A target grid assembly incorporating various features of the present invention is illustrated generally at 10 in the figures. The target grid assembly 10 includes a target grid for use with a conventional target assembly. The target grid defines a simpler grid design and is easier to manufacture than the hexagonal grid of the prior art, while being capable of providing support to a target window similar to that of the hexagonal grid. In the preferred embodiment, the target grid assembly 10 is designed to include a means for helium cooling the target window and target material such that the target assembly in which the target grid assembly is employed can remove more heat and operate under higher pressure and higher beam currents than the target systems of the prior art. The target grid assembly 10 of the present invention includes at least a target grid 16. The target grid 16 defines a target grid portion 20 which is linear in design, as shown most clearly in the exploded view of FIG. 3b. More specifically, the target grid portion 20 defines a plurality of grid supports 22 or septa which are configured to form a plurality of oblong openings 24. The grid supports 22 are minimized in thickness to increase the transparency of the grid portion 20 and more specifically, the grid support thickness is on the order of 0.010xe2x80x3 thick. The target grid 16 also defines at least one fluid cooling channel around its periphery (not shown). The target assembly 60 in which the target grid assembly 10 is employed is conventional and includes a target window 63, a target body 64 and a target housing. The target body 64 defines a reservoir 65 for receiving target material 66 therein The target window 63 is positioned against the target body 64 to seal the target reservoir 65, and the target housing (not shown) serves to enclose the target grid assembly 10, the target window 63 and the target body 64 therein. The target window 63 is supported by the downstream side 54 of the grid supports 22 of the target grid 16, as shown most clearly in the schematic diagram of FIG. 2. The target grid portion 20 serves to divide the target window 63 into several smaller subwindows With the use of a target grid 16 to support the target window 63, the target window 63 can be fabricated from materials which lack tensile strength but provide other benefits. For example, copper beryllium provides high thermal conductivity but lacks tensile strength. The target grid 16 eliminates the drawbacks with respect to the target window""s lack of strength. It will be noted that the oblong geometry of the openings 24 of the target grid portion 20 of the present invention does not support the target window 63 as effectively as the hexagonal geometry of the prior art target grid, shown in FIGS. 1a and 1b for the same characteristic dimensions. The characteristic size (width) of the oblong openings 24 or linear grid must be scaled accordingly to maintain the window strength of a hexagonal geometry. In the preferred embodiment, the target grid assembly 10 further includes a vacuum window 12. The vacuum window 12 is positioned on the upstream side 56 of the target grid supports 22, as shown most clearly in FIG. 2. The target grid 16 further defines a helium input 26 and a helium output 28, shown most clearly in FIG. 3a.  It is desirable to establish a good contact between the vacuum window 12 and the face of the target grid supports 22. Moreover, it is desirable to increase the operating pressure of the helium recirculating system. For these reasons, it is preferable to employ an interception grid 32 to support the vacuum window 12. The interception grid 30 defines an interception grid portion 32 which defines a plurality of grid supports 34 or septa. The grid supports 34 are configured to form a plurality of oblong openings 36 similar in configuration to the oblong openings 24 defined by the target grid portion 20, as shown in FIGS. 2-4. The vacuum window 12 is positioned between the interception grid supports 34 and the target grid supports 22, as shown most clearly in FIG. 2. It will be noted that it is preferable that the interception gird supports 34 and the target grid supports 22 are aligned. In the preferred embodiment, the interception grid 30 further defines at least one fluid cooling channel on its periphery (not shown). A helium space 40 is defined between the vacuum window 12 and the target window 63. More specifically, the area defined by the target grid oblong openings 24 and enclosed between the vacuum window 12 and the target window 63 serves as the helium space 40. Referring to the exploded views of FIGS. 3a and 3b, a slotted O-ring 42 is positioned between the target grid 16 and the vacuum window 12. More specifically, the O-ring 42 defines two spaced apart slots 44, 46. These slots 44, 46 are spaced to coincide with helium input 26 and the helium output 28, respectively, of the target grid 16 and run perpendicular to the upper portion 23 and lower portion 25, respectively, of the oblong openings 24 defined by the target grid portion 20. FIG. 2 illustrates a schematic diagram of a particle beam 68 striking the preferred embodiment of the target grid assembly 10 to ultimately bombard the target material retained in the target body 64 of a target assembly 60. The interception grid supports 34 intercept a portion of the incoming beam 68 thereby causing the supports 34 to heat up. This heat is removed by the cooling water or fluid circulating through the fluid cooling channels (not shown). Because the interception grid supports 34 are not in contact with the target window 63, the heat absorbed therein does not contribute to the heat in the target window 63 and target material 66. More specifically, without the interception grid 30, the target grid supports 22 would absorb heat from the incoming particle beam 68 which would contribute to the heat in the target window 63 and target material 66. It will be noted that heat absorbed in the target grid 16 is removed by fluid cooling channels (not shown) around the target grid periphery. The remainder of the beam 68 passes through the vacuum window 12 and target window 63 to bombard the target material 66 retained in the target body reservoir 65. As the target material 66 is bombarded, it heats up and this heat is conducted to the target window 63. Cooling the target window 63 with helium will serve to cool the target window 63 and the target material 66. Further, the vacuum window 12 will be cooled. In the prior art, a high velocity helium jet is utilize to cool target windows. In the present invention, a helium cooling regime 50 is established. This helium cooling regime 50 is high density and therefore, high mass flow and high heat capacity. This high density regime 50 is more effective at heat removal than the helium jet of the prior art. However, the vacuum window 12 must be able to tolerate the higher pressure of the helium cooling regime 50. It is an added benefit of the preferred embodiment of the present invention that the interception grid 30 upstream of the vacuum window 12 provides precisely the necessary support for such a scenario. In FIG. 2, it will be noted that the vacuum window 12 and target window 63 are bowed out between each of their respective grid supports 34, 22. The high pressure in the target reservoir 65 bows the target window 63 and the high pressure of the helium cooling regime bows the vacuum window 12. Helium flows into and out of the helium space 40 via the helium input 26 and the helium output 28 of the target grid 16, respectively. The vacuum window 12 and target window 63 serve as upper and lower boundaries of the helium cooling regime 50. Helium flows into the upper portion 23 of each oblong opening 24 via the first slot 44 defined by the O-ring 42 and exits the lower portion 25 of each oblong opening 24 via the second slot 46 of the O-ring 42. The close contact established between the vacuum window 12 and the target grid supports 22 via the interception grid supports 34 serves to minimize cross flow of helium from one oblong opening 24 to another such that the helium cooling regime 50 can be established and maintained. From the foregoing description, it will be recognized by those skilled in the art that a target grid assembly offering advantages over the prior art has been provided. Specifically, the target grid assembly includes a grid which defines a configuration such that helium cooling to cool the target window and target material can be employed, while being capable of providing support to the target window similar to that of the hexagonal grid of the prior art. Further, the linear target grid assembly can remove more heat for the front (upstream) of the target than gridded window systems of the prior art. Further, the grid defines a simpler grid design which is easier to manufacture than the hexagonal grid of the prior art. Further, the target grid assembly can withstand higher pressures and higher beam currents than the non-gridded assemblies of the prior art. Moreover, the thickness of the grid septa or supports is minimized for transparency. While a preferred embodiment has been shown and described, it will be understood that it is not intended to limit the disclosure, but rather it is intended to cover all modifications and alternate methods falling within the spirit and the scope of the invention as defined in the appended claims.