3D TWT modeling and experimental validation

Summary form only given. The ability to fully simulate the 3D effects of RF and space charge forces on the electron beam of a helix TWT during energy extraction is important for TWT design and optimization. A helix TWT simulator, CHRISTINE3D, has been developed to achieve this capability. Validation of code results is an important step to address before the code can be reliably used for TWT design. CHRISTINE3D has been used to compute the output power and efficiency of a C-Band TWT as a function of frequency and input drive power and showed excellent agreement with experimental results. The greatest value of the model, however, lies in its ability to calculate the full set of phase space information of all particles as they travel along the length of the simulation. This allows the determination of such parameters as beam expansion and spent beam distribution which can then be used to determine magnetic field profiles and collector design. This information is not available in a 1 D simulation and is critical for overall TWT design optimization. The TWT used for the validation exhibits forward helix intercept current for certain magnetic field configurations and is a good vehicle to test the beam expansion predictions of the simulator. Comparison of computed results with experimental data will be reported for several experimental configurations. Also, several spent beam distributions were computed for varying values of circuit efficiency. These distributions were also measured for comparison with prediction. The results presented will show good correlation between experiment and simulation for the wide range of magnetic field and distribution functions studied. These results give confidence in the predictive capability of the CHRISTINE3D TWT simulator and in the ability to understand and to continually improve TWT performance through simulation.