Fabrication and assembly of the gyrotron multi-stage depressed collector prototype at KIT

In this paper details of the fabrication and assembly of the first Multi-stage Depressed Collector (MDC) prototype developed at KIT for megawatt-class gyrotrons are presented. Utilizing the E×B drift concept for electron trajectory separation, the cylindrical Short-Pulse (SP) MDC prototype features a design compatible with applications in different fusion gyrotrons at KIT, for W7-X, ITER, and DEMO. The fabrication process includes inner electrodes out of copper-chromium-zirconium (CuCr1Zr) with a triple helix isolation design, modular vacuum housing consisting of four parts, and additional external coils for electron beam confinement. Detailed assembly procedures are provided for two configurations: the 170 GHz 2 MW coaxial cavity gyrotron and the W7-X upgrade SP gyrotron. The successful manufacturing of the modular collector and a robust design for vacuum tightness are demonstrated. The prototype is now primed for verification in the KIT FULGOR test stand with the W7-X gyrotron for validation of the E×B drift concept and improvement of the gyrotron efficiency. This comprehensive work bridges theoretical concepts with practical implementation, offering insights crucial for refining and advancing MDCs for megawattclass gyrotrons for fusion applications.