Preliminary study of dual annular multiple-beam cathode for V-band coaxial transit-time oscillator

Abstract

Since the research toward high-power millimeter-wave generator becomes a tendency in high-power microwave, overmoded structure with the high-order mode has been a considerable interest because of its potential to increase power handling capacity (PHC). To expand the PHC of V-band transit-time oscillator and excite higher mode TM03, a dual annular multiple-beam cathode has been proposed. In the geometric structure of the dual annular multiple-beam diode, cathode rods around two concentric circles are uniformly placed on cathode base, and each circle has several graphite rods. Because of space charge shielding effect and fluctuation of electron beam, explosive emission current of inner and outer cathode circles is difficult to be balanced, and the electron beam transmission rate is not very high. To solve those two problems, the relative length (ΔL) and the relative radius (Δr) between the inner and outer cathode circles are optimized to obtain balanced currents of inner and outer beams and a good transmission rate. In this paper, the preliminary study of a dual annular multiple-beam cathode is carried out by optimizing the cathode structure. When ΔL and Δr are equal to 2.5 and 4 mm, respectively, the dual annular multiple-beams cathode can provide 2.71 kA uniform intense relativistic electron beams under 421 kV, and the magnetic field is 1.2T. As a simulation result, explosively emitted and the 95.2% of total beam current transmission rate can be reached.