Coupled-cavity monotron

We demonstrate that on considering an electric-field longitudinal profile in the shape of a two-level transition curve the monotron conversion efficiency can attain values in excess of 30%, 1.5 times as high as that obtained from the conventional uniform field distribution. This is accomplished by using two cavities electromagnetically coupled by an annular slit crossed by an electron stream. A two-cavity monotron is developed to operate in the TM₀₂₀ mode at 6.6 GHz when self-excited by a 20 keV, 50 A hollow electron beam. The device operation is examined through a 2 1/2-D particle-in-cell (PIC) simulation giving a 33.0% conversion efficiency.