The New Fabrication Method for a Periodic Permanent Magnet (ppm) C-band (5712 Mhz) Klystron

PPM focusing is quite an attractive scheme, since it eliminates the focusing solenoid (and its power supply) from the klystron. However, one technical difficulty lies in how to integrate the magnetic-circuit, which is relatively complicated, into the vacuum tube. We have solved this problem by introducing a new fabrication technique of metal-to-metal diffusion-bonding by hot-isostatic-pressing (HIP). After simply stacking alternatively the disks made of magnetic stainless-steel (Mag-SUS) and oxygen-free-copper (OFC) without any brazing-material, they were bonded together by pressing with a high-pressure (1200-kgf/cm) at a high temperature (800-°C) for 2 hours. Machining this bonded block produces the drift-tube for the PPM-klystron. We chose the neodymium magnet because of its high maximum BH-product (>40 MGOe), while still having relatively low cost. A 50-MW class C-band PPM klystron is under fabrication. Already magnetic field measurement has been performed, and the axial-field profile was confirmed to be within tolerance. A high power test is scheduled in July 2000.