Design and commissioning of a multiharmonic bunching system for the high-intensity heavy-ion accelerator facility

Abstract: The High Intensity Heavy Ion Accelerator Facility (HIAF) is currently under construction in China for multidiscipline research. The front-end section has been completed and is currently undergoing commissioning. To optimize beam quality, an external multiharmonic buncher (MHB) that reduces longitudinal emittance has been installed before the radio frequency quadrupole. The MHB system includes both cavity and low-level radio frequency (LLRF) system designs. The cavity consists of a quarter-wave resonator and a half-wave resonator, with a single grid-less gap, capable of providing the required voltage of 1.5 kV. With the newly developed multiharmonic LLRF control system, precise individual control of the four harmonic components can be achieved,enabling flexible synthesis of various waveform configurations. The buncher can generate a 1 ^st + 2^nd + 3^rd + 4^th harmonic bunching electric field with a fundamental frequency of 40.625 MHz, or a 1 ^st + 2^nd harmonic bunching electric field with a fundamental frequency of 81.25 MHz. In addition, the first O⁶⁺ beam commissioning results of front-end accelerator are presented herein, providing insights into the contribution of the MHB.