Progress of three-layer structure RFQ linacs and the applications

The three-layer structure RFQ linac features a simple structure and fabrication method while providing excellent electrical performance. The main components of the four-vane RFQ cavity (four vane electrodes and the cavity body) are divided into three parts, and machined with high precision from blocks of oxygen-free copper. Since no thermal processes such as brazing or welding are required, the machining accuracy of the vane electrodes is preserved. It has therefore been adopted for heavy-ion therapy injectors and proton accelerators for compact neutron sources. As an advanced development, a tuner-less frequency adjustment technique has been realized. Furthermore, the development of the energy-tunable cavity addresses the inherent limitation of RFQs in beam energy variability.