Periodic structures manufactured by 3D printing for electron beam excitation of high power microwave sources

A Two-dimensional (2D) Periodic Surface Lattice (PSL) can produce distributed feedback in high power microwave sources driven by an oversized electron beam of annular geometry. Such 2D periodic structures can be formed in cylindrical waveguide with a grating machined on the walls, where the diameter of the waveguide is larger than the wavelength λ (D >> λ). In this case localised surface fields can be excited around the perturbations if the structure is radiated by an external source (for example an electron beam). Experiments were conducted using a velvet cathode electron gun with the electron accelerating voltage produced by a cable Blumlein generator. 'Additive Manufacturing' or '3D printing' was used to construct a silver 2D PSL quickly, efficiently and relatively inexpensively. The electron beam formed within an 18 mm bore 1.8 T solenoid was transported through the 7.2 mm inner diameter silver 2D PSL beam-wave interaction region. An 80 kV, 100 A electron beam with an outer diameter of 4 mm and inner diameter of 2mm which was approximately 1.8 mm away from the inner surface of the 2D PSL corrugation was measured. Millimetre wave radiation at a frequency of 80GHz at an output power of 130 ± 30 kW corresponding to an operating efficiency of 1.7 % was measured.