Development and commissioning of the pre-bunching system at RAON

Abstract

The low-energy experimental systems at the Rare isotope Accelerator complex for ON-line experiments (RAON) consist of the Korea Broad Acceptance Recoil spectrometer and Apparatus (KoBRA) and the Nuclear Data Production System (NDPS). Controlling the beam repetition rate is essential for Time-of-Flight (TOF) experiments because too frequent primary beam bunches can cause overlapping of secondary beam bunches, leading to uncertainty in the TOF measurements of secondary beam particles. This study presents the design, fabrication, and commissioning results of a pre-bunching system at RAON to manage the beam repetition rate. The developed pre-bunching system combines a fast chopper with a Double Gap Buncher (DGB). The fast chopper utilizes the existing slow chopper electrodes by adapting them to generate pulsed beams with controlled repetition rates. Meanwhile, the DGB reduces the pulse length to less than one Radio Frequency Quadrupole (RFQ) cycle at the RFQ entrance, thereby minimizing the formation of satellite bunches during RFQ acceleration. Simulations using the SIMION code validated the pre-bunching system's performance prior to beam commissioning. Additionally, we have developed RF voltage-boosting circuits to supply high-voltage RF to both the fast chopper and the DGB. Following the design and development phase, we performed beam commissioning with Ar8+ ion beams, which successfully demonstrated the generation of single bunches for the first time at RAON, confirming the performance of the pre-bunching system.