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Description
This work presents the design and multi-code simulation of a 10 MW-class L-band (1.3 GHz) multi-beam klystron (MBK) intended as a high-efficiency RF power source for superconducting linear accelerators. The design covers the electron gun, magnetic focusing system, RF interaction structure, output window, and collector. Six low-perveance (0.57 μP) beamlets extracted at a cathode voltage of -115.1 kV provide a total space-charge-limited current of 134.8 A, corresponding to a DC beam power of 15.5 MW. The maximum surface electric field is limited to 5.8 kV/mm, approximately 27% below the estimated breakdown limit, while the cathode loading is maintained ~2.0 A/cm² to ensure long cathode life. A ten-coil confined-flow focusing system transports the beam with an average beam radius of 5.1 mm, a magnetic field ripple of 5.0%, and a fill factor of 0.57. The 2D and 3D magnetic field simulations agree within approximately 0.2%. Beam dynamics simulation cross-validated using AJDISK (1D), KlyC (1.5D), and KlyC (2D) predict RF efficiencies of 69–74% and output powers of 10.5–11.3 MW, exceeding the 10 MW design target. The RF output window achieves an S11 of −35.4 dB and a VSWR of 1.034 at 1.3 GHz. Coupled thermal-mechanical analysis gives a peak temperature of 41.4 °C, corresponding to a temperature rise of approximately 16.4 °C, and a maximum von Mises stress of 0.0197 GPa. For the collector, a grooved, double-walled structure reduces the peak surface temperature from 259.6 °C to 183.5 °C under the full 15.5 MW DC beam, demonstrating adequate thermal and structural margins throughout. These results confirm the feasibility of the proposed 10 MW L-band MBK design and provide a comprehensive simulation basis for subsequent prototype fabrication and experimental validation.
