Patent Number: 
Section: claims

1. A diagnostic resonant cavity for use in determining characteristics of a charged particle beam traveling along a beam line of a charged particle accelerator, comprising two electrically conductive opposing end walls spaced apart from one another by an electrically conductive tubular wall, said end walls having openings centered therein for interposition of the cavity in the beam line by connection of said end walls to a beam tube having a central longitudinal axis defining the nominal path of travel of the charged particle beam, and an even plurality of at least four pairs of electrically conductive rods extending into said cavity from said end walls, each of said pairs of rods consisting of two rods extending inwardly and coaxially toward one another from said two opposing end walls and extending parallel to said central longitudinal axis said of said beam tube, said two rods of each pair of opposing rods being spaced from one another so as to form a capacitative gap between one another, and wherein said pairs of rods are equally spaced azimuthally in a symmetrical array around said central longitudinal axis of said beam tube. 2. The diagnostic resonant cavity defined in claim 1 wherein said end walls are each substantially planar and extend parallel to one another. 3. The diagnostic resonant cavity defined in claim 2 wherein said end walls are each orthogonal to said central longitudinal axis of said beam tube. 4. The diagnostic resonant cavity defined in claim 3 wherein said tubular wall of said diagnostic resonant cavity is cylindrical. 5. The diagnostic resonant cavity defined in claim 4 wherein said rods extend from said end walls from points contiguous to said openings in said end walls. 6. The diagnostic resonant cavity defined in claim 5 wherein said rods extend tangentially to said openings in said end walls. 7. The diagnostic resonant cavity defined in claim 6 comprising four pairs of rods to enhance the shunt impedance of the quadrupole resonant mode of the cavity. 8. The diagnostic resonant cavity defined in claim 6 comprising, six pairs of rods to enhance the shunt impedance of the sextupole resonant mode of the cavity. 9. The diagnostic resonant cavity defined in claim 1 comprising four pairs of rods to enhance the shunt impedance of the quadrupole resonant mode of the cavity. 10. The diagnostic resonant cavity defined in claim 1 comprising six pairs of rods to enhance the shunt impedance of the sextupole resonant mode of the cavity. 11. A diagnostic resonant cavity for use in determining characteristics of a charged particle beam traveling along a beam line of a charged particle accelerator, comprising first and second electrically conductive opposing end walls spaced apart from one another by an electrically conductive tubular wall, said end walls having openings centered therein for interposition of the cavity in the beam line by connection of said end walls to a beam tube having a central longitudinal axis defining the nominal path of travel of the charged particle beam, and an even plurality of at least four electrically conductive rods extending into said cavity from said first end wall, each of said rods extending inwardly in a direction parallel to said central longitudinal axis said of said beam tube, and each of said rods having an end distal from said first end wall, said distal end of each rod being spaced from said second end wall so as to form a capacitative gap between the rod and said second end wall, and wherein said rods are equally spaced azimuthally in a symmetrical array around said central longitudinal axis of said beam tube. 12. The diagnostic resonant cavity defined in claim 11 wherein each of said rods extends a distance greater than the major length of said cavity along said axis of said beam tube. 13. The diagnostic resonant cavity defined in claim 12 wherein said tubular wall of said cavity is cylindrical in cross section. 14. The diagnostic resonant cavity defined in claim 13 comprising four rods to enhance the shunt impedance of the quadrupole resonant mode of the cavity. 15. The diagnostic resonant cavity defined in claim 13 comprising six rods to enhance the shunt impedance of the sextupole resonant mode of the cavity. 16. The diagnostic resonant cavity defined in claim 11 wherein said rods extend tangentially to said openings in said end walls.