New 2.5D code for simulation of nonlinear multisignal amplification in a wideband helix TWT

Summary form only given. In this paper, we describe a new 2.5D code for simulation of a helix TWT, developed by Saratov State University and SPRC Istok company. Such codes are important for numerical modeling of broadband high-gain traveling wave tubes (TWT) that are widely employed in satellite communications and other related applications. Amplification of a multifrequency signal is simulated by the method of fundamental frequency. The beam is modeled with a set of macro-particle disks and rings having finite length along z-axis. To find trajectories of the particles three-dimensional relativistic equations are solved. The method of space-charge simulation is similar to that of the CHRISTINE-3D code. The space charge and current densities are represented as harmonic series in z. The amplitudes of the harmonics are calculated with the particle-in-cell (PIC) method. Thereupon Helmholtz equations are solved by finite-difference method and transversal distributions of the electric and magnetic fields of each harmonic are found. Electro- and magnetostatic fields of the beam are considered in a similar way. The code has been applied successfully in Istok Corp. for the design of wideband TWT amplifiers.