Dual-mode high-voltage sawtooth wave buncher for low-energy ion injection at HIRFL-SFC cyclotron

Background Sawtooth wave buncher is widely used in low-energy ion injection at cyclotron accelerators. Its performance significantly impacts on the intensity of ion beam delivered to experimental terminals. In order to meet the high-intensity requirement of physical experiments, we upgrade the existing B02 buncher in the axial injection line of the SFC with the dual-model sawtooth wave buncher for low-energy ion injection. Methods We use a three harmonics synthesis method in the dual-sawtooth wave buncher. First, we use three harmonics to generate a low-level sawtooth wave. Second, the low-level wave is amplified by a broadband amplifier to generate high voltage at a single-gap electrode. Third, the electrode is matched to the amplifier by a 1:9 transmission line transformer. Results The new buncher has been installed online since September 2022. Our tested results show that the buncher is capable of being operated at the full-frequency mode and half-frequency mode with the corresponding frequency ranging from 2.75 to 8.0 MHz and 5.5 to 16.0 MHz, respectively. The effective voltage can be up to 2.54 kV and 1.6 kV, respectively. Also, the sawtooth wave buncher works reliably, and a 4.5–8.6 times gain in the beam intensity is achieved. Conclusion By using the three-harmonic synthesis method, a new dual-mode high-voltage sawtooth wave buncher has been built. This sawtooth wave buncher has succeeded in being applied with the high buncher voltage over a wide frequency range with good reliability and stability. This newly-built sawtooth wave buncher significantly increases the ion beam current for low-energy ion injection at the HIRFL-SFC cyclotron.