Overmoded cavity bounded by first and second grids for providing electron beam/RF signal interaction that is transversely distributed across the cavity
View Patent ↗An overmoded distributed interaction network is provided that generates high peak and average RF power amplification at high frequencies. A series of overmoded cavities are bounded by parallel or concentric grids that may be separated by metallic spacers adapted to function as a photonic bandgap circuit to suppress competing electromagnetic modes. The selected electromagnetic modes have wavelengths much shorter than the lateral dimension of the grids, allowing the beam-wave interaction to be distributed transversely for improved interaction efficiency. The grids may optionally be slotted and arranged to provide a serpentine traveling wave tube configuration.
1. An overmoded distributed interaction network (ODIN) configured to support an interaction between an electron beam and a radio frequency (RF) signal, wherein the ODIN comprises:
an overmoded cavity bounded by a first grid and a second grid, wherein the first grid and the second grid each includes a plurality of apertures arranged to enable the electron beam to pass through the overmoded cavity along a beam direction from the first grid to the second grid; wherein:
the overmoded cavity is oriented transverse to the beam direction;
the first grid and the second grid are separated by a distance of the order of one radian of electron beam transit angle;
the overmoded cavity is adapted such that at least one electromagnetic field mode is supported within the overmoded cavity, the supported electromagnetic field mode having a wavelength smaller than a dimension of the first grid measured along a direction substantially perpendicular to the beam direction; and
wherein the interaction between the electron beam and the RF signal is distributed within the overmoded cavity transverse to the beam direction.
2. The ODIN of claim 1 , further adapted to include an RF coupling circuit operatively connected to the overmoded cavity to couple the RF signal to or from the overmoded cavity.
3. The ODIN of claim 1 , wherein the first grid and the second grid each comprise concentric cylinders and the beam direction is substantially radial.
4. The ODIN of claim 3 , wherein the at least one supported electromagnetic field mode has a transverse electromagnetic mode (TEM) characteristic.
5. The ODIN of claim 1 , wherein the first grid and the second grid each comprise parallel planar grids positioned substantially perpendicular to the beam direction.
6. The ODIN of claim 1 , wherein a distance between the first grid and the second grid is maintained by a plurality of spacers.
7. The ODIN of claim 6 , wherein the plurality of spacers is formed from a material selected to be one of a metallic material and a dielectric material.
8. The ODIN of claim 6 , wherein the plurality of spacers is arranged to form a photonic bandgap circuit operative to attenuate one or more electromagnetic field modes within the overmoded cavity.
9. The ODIN of claim 1 , comprising additional transversely overmoded cavities formed by stacking additional grids parallel to the first grid and the second grid, each one of the additional grids comprising:
a plurality of apertures arranged to allow passage of the electron beam; and
a plurality of spacers arranged to maintain a selected distance to an adjacent grid.
10. The ODIN of claim 9 , configured to operate as a coupled-cavity traveling wave tube and including an RF coupling circuit comprising:
an input waveguide coupled to at least one of the transversely overmoded cavities; and
an output waveguide coupled to at least one of the overmoded cavities which is not coupled to the input waveguide.
11. The ODIN of claim 10 , wherein each of the parallel grids is further adapted to include a coupling slot such that each of the transversely overmoded cavities is electromagnetically coupled to an adjacent transversely overmoded cavity via the respective coupling slot.
12. The ODIN of claim 11 , wherein the coupling slots in adjacent parallel grids are arranged in a staggered configuration such that an electromagnetic wave follows a serpentine path between the input waveguide and the output waveguide.
13. In an overmoded distributed interaction network (ODIN) comprising at least a first grid and a second grid each having a plurality of apertures and bounding an overmoded cavity, a method of creating a spatially distributed interaction between an electron beam and a radio frequency (RF) signal comprises the steps of:
locating the first and second grids such that they are separated by a distance of the order of one radian of electron beam transit angle;
injecting the electron beam into the overmoded cavity in a beam direction through the plurality of apertures from the first grid to the second grid, wherein the overmoded cavity is oriented in a direction transverse to the beam direction; and
exciting the RF signal in the transversely overmoded cavity such that an electromagnetic field mode is supported that has a wavelength shorter than a dimension of the first grid measured in a direction substantially perpendicular to the beam direction.
14. The method of claim 13 , further comprising the step of dividing the electron beam into a set of electron beamlets, each beamlet arranged to align with a corresponding one of the plurality of apertures, such that electron beam impingement on the first grid and second grid is reduced.
15. The method of claim 13 , further comprising the step of bunching the electron beam before entering the overmoded cavity.
16. The method of claim 14 , wherein the step of dividing the electron beam into a set of electron beamlets further includes enhancing one or more electromagnetic modes by selectively directing the electron beamlets through certain ones of the plurality of apertures located in regions where the one or more electromagnetic modes have peak field intensities.
17. The method of claim 13 , wherein the step of coupling the RF signal into the overmoded cavity further includes the step of rejecting selected electromagnetic modes by positioning spacers between the first grid and second grid to form a photonic bandgap circuit within the overmoded cavity to attenuate the selected electromagnetic modes.