Advanced modeling of Helix TWTs

Summary form only given. The Tube Research, Development, and Engineering (TRD&E) group of Northrop Grumman ESID-ES has invested a significant amount of effort improving our ability to accurately model helix TWTs. Enhanced design capability for subsystems such as the electron gun, circuit, and the depressed collector has lead to advances in the rapid prototyping of new designs and the optimization of existing TWT products. In some cases, new codes have been developed for use by the tube industry, and Northrop Grumman has been proactive in benchmarking and determining their potential for improved modeling. In other cases, existing codes, such as particle-in-cell (PIC) and 3D finite-difference codes, have been applied to helix TWT design. Our experience with these codes and their effectiveness in TWT modeling will be discussed. Comparisons to experimental data will be made wherever possible. For circuit design the one-dimensional parametric code CHRISTINE has proved particularly useful for rapid evaluation and optimization of helix TWT circuits. In the case of the Northrop Grumman C-Band MPM TWT the success of this modeling effort has been presented elsewhere. Here we will discuss the effectiveness of the CHRISTINE code in modeling the performance of multi-octave TWTs, in particular the 4.5-18 GHz, 125 W Ultraband MPM TWT. Harmonic performance and multitone operation will be compared with experimental data.