Application of an Improved Large-Signal Code TESLA-2.5D to the Modeling of a 45 MW Relativistic Klystron

We present results of the very first successful application of the 2.5-D large-signal klystron code TESLA to the modeling of an existing, mildly relativistic S-band klystron VKS-8245C, which was manufactured and tested at Microwave Power Products (MPPs), Inc., formerly CPI, Palo Alto, CA. The device consists of five single-gap cavities, uses an electron beam of 313 kV voltage and 336 A current and produces 45MW of peak output power. Because of its compactness, this advanced klystron design is characterized by a significant role of 2-D effects, including active rotation and radial motion of the electron beam’s particles. Therefore, accurate modeling of this klystron requires the use of an advanced, fully 2-D computational tool. To validate the code TESLA-2.5D algorithm, we have compared its predictions for this klystron with the predictions of the Particle-in-Cell (PIC) code MAGIC-2D. The existing code TESLA-2.5D algorithm initially made wrong predictions for particles’ trajectories and drive-curve, which were found to be very different from the ones computed by MAGIC-2D. After detailed investigations, we have found and corrected the problem in the TESLA-2.5D algorithm to ensure a proper choice for the sign of the RF field’s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{\theta }$</tex-math> </inline-formula>–component, which becomes critically important for accurate modeling of the relativistic beam’s dynamics in high-power devices. Results of this our study highlight the importance of the relativistic effects, which already cannot be ignored. As result of the made correction, code TESLA-2.5D is now capable of properly modeling the dynamics of the relativistic electron beam, including its pinching. The improved version of the code TESLA-2.5D shows good agreement with the predictions of MAGIC-2D and available test data. As we have demonstrated, the corrected TESLA-2.5D algorithm is capable of accurately modeling the advanced relativistic klystron with all its challenging features included. For additional comparative analysis, we have also performed modeling by using simplified klystron settings: first applying corrected code TESLA-2.5D, and then its 1.5-D version (TESLA-1.5D); these results were compared with MPP’s 1-D code LSCEX.