High precision tuning of RF cavity for 6 MeV SKKU X-band medical LINAC

Abstract

An X-band electron LINAC comprising 23 cells was fabricated and tuned for radiation therapy. The fabrication process used oxygen-free high-conductivity copper, which was divided into roughing and finishing stages to minimize machining errors. Resonance frequency measurements and tuning were performed for the half-cell, the unit cell with two half-cells combined, and all cells after assembly. Finally, the electric field inside the entire RF cavity was measured and tuned using a bead-pull test. The reason for the multi-step measurement and tuning was to minimize the number of tunings. Most of the tuning was done in the direction of increasing the frequency, and only a few were done in the direction of decreasing the frequency. All cells were tuned the same way. The finalized cavity had a resonance frequency of 9.306 GHz and a coupling coefficient of 1.277. Performance validation was performed through the percentage depth dose (PDD) test, confirming good agreement with the results for 6 MV X-rays.