Recent advances with the electrostatically focused high power amplifier klystrons

In an electrostatically focused klystron (ESFK) the electron beam is focused by a periodic system of electrostatic lenses. These lenses are formed by the walls of successive cavities and a ring shaped electrode located between adjacent cavities. The latest model of the ESFK employs a solid beam of circular cross section having a perveance of 0.7 × 10^-6a/v^3/2. By a proper choice of lens dimensions, optimum operating performance of the tube is achieved with the lens voltages equal to cathode voltage. The tube incorporates four cavities and is of all metal-ceramic construction. Cavities and collector are water-cooled. The rf output coupler is a standard wave-guide flange containing a beryllia window. At the present moment, the tube which was designed for an average power output of 5 kw is still being tested. With a beam voltage of 25 kv, and a frequency of 2.8 Gc, the following, results have been achieved to date: Power output 28 kw peak Saturated gain 30 db Small Signal Gain > 67 db Saturated efficiency 41% All measurements were taken at a duty cycle of 0.003. With a previous model of the ESFK, which was limited only by the power handling capability of the coaxial rf window, an average rf output power of 850 watts was achieved.