Design, fabrication, and testing of an X-band 9-MeV standing-wave electron linear accelerator

In this study, an X-band standing-wave biperiodic linear accelerator was developed for medical radiotherapy that can accelerate electrons to 9 MeV using a 2.4-MW klystron. The structure works at π/2 mode and adopts magnetic coupling between cavities, generating the appropriate adjacent mode separation of 10 MHz. The accelerator is less than 600-mm long and constitutes four bunching cells and 29 normal cells. Geometry optimizations, full-scale radiofrequency (RF) simulations, and beam dynamics calculations were performed. The accelerator was fabricated and examined using a low-power RF test. The cold test results showed a good agreement with the simulation and actual measurement results. In the high-power RF test, the output beam current, energy spectrum, capture ratio, and spot size at the accelerator exit were measured. With the input power of 2.4 MW, the pulse current was 100 mA, and the output spot root-mean-square radius was approximately 0.5 mm. The output kinetic energy was 9.04 MeV with the spectral FWHM of 3.5%, demonstrating the good performance of this accelerator.