Optimization and Upgrade of Slow Extraction Control System for HIRFL CSR Main Ring

The heavy ion beam from Heavy Ion Research Facility in Lanzhou (HIRFL) CSR Main Ring (CSRm) is slowly extracted by using a third-order resonance driven by sextupole magnets and delivered to various experimental facilities. The slow extraction is driven by the transverse radio frequency knockout (RF-KO) exciter. Many physics and radiation medicine experiments require high-quality spill-structure. In other words, the extracted spill should have flat structure and low ripple noise [1]. Therefore, a novel RF-KO exciter and spill feedback control system has been implemented and tested in CSRm. INTRODUCTION The HIRFL accelerator complex is illustrated in Fig. 1. The particles accelerated by CSRm are slowly extracted to external experimental terminals, or extracted in fast extraction mode to CSR Experiment Ring (CSRe). In slow extraction mode, many physical, material, biological, and medical experiments require high-quality spill that has flat structure and low ripple noise. For CSRm, the resonant slow extraction is driven by RF-KO exciter. In the new spill control system of CSRm, the host machines are employed to calculate amplitude modulation curve and spill duty factor, publish the control variables, and manage the various parameters that are often stored in the database. In addition, two FPGA boards are dedicated to control RF power amplifier and a pair of fast quadrupole (FQ) magnets. Figure 1: HIRFL accelerator complex. SPILL CONTROL In the HIRFL, the particles are extracted slowly out of the CSRm by using RF-KO exciter. The two FQ magnets are additionally used to achieve better spill quality. As shown in Fig. 2, the typical shapes of spill are achieved by RF-KO extraction without feedback unit at CSRm after upgrading. Fig. 3 shows the block diagram of the new spill control system. In the RF-KO method, the beam is partially moved into resonance by transverse excitation. The suitable parameters of the RF-KO exciter dose improve efficiency and spill quality reasonably. In the feedback unit, the spill signal is used to calculate the exciting signal for FQ magnets which is used to suppress the spill ripple noise and make rectangular-shaped spill structure. Figure 2: Typical spill shapes archived by RF-KO extraction without feedback control at CSRm. Here: Carbon beam, energy E = 190, 260, 330, and 400 MeV/u. Host Machine (Industry PC) FPGA Target Database