Pic Simulations of a X-Band Traveling-Wave Tube Using Two Spiral Metamaterials

We developed a new X-band traveling-wave tube using two-spiral metamaterials
^1,2
which form a regular hexagonal ring unit cell. An array of these form a slow wave structure (SWS) in a circular waveguide. A transparent cathode with 6 emitters is used to generate the electron beam. The outer radius of the hexagonal unit cell is 4.3 cm while the radius of the inscribed circle is 3.723 cm. The hexagonal unit cell is connected to a structure with radius 1.32 cm and is inside a cylindrical waveguide of 5.63 cm radius. The transparent cathode radius is 1.5 cm and its length is 3.0 cm. The two spiral metamaterial unit cell is scaled to make the TM
01
mode operate at 8.8 GHz with output power as high as 378 MW with 20% efficiency when an applied voltage of 965 kV and total beam current of 2 kA are used. These results show the advantage of using metamaterials as a SWS in a traveling-wave tube with low start-current.