A new 4th Generation Storage Ring (4GSR) will be constructed in Ochang, South Korea, by the end of 2029. A technical design review for the Korea 4GSR was completed at the end of 2023. The storage ring has a circumference of 799 meters and is designed for a maximum current of 400 mA at 4 GeV electron beam energy. The target emittance is below 100 pm-rad, with a calculated emittance of 62 pm-rad—100 times smaller than that of PLS-II, a 3rd-generation storage ring in Korea. The RF system for the Korea 4GSR comprises 10 normal-conducting cavities, a low-level RF (LLRF) system, a high-power RF (HPRF) system, and additional components. To ensure beam stability, Higher Order Mode (HOM)-damped cavities have been implemented. Additionally, we plan to install harmonic cavities to improve beam lifetime and reduce wakefields. For the LLRF system, we aim to apply a new digital feedback control scheme and implement FPGA chips. For the HPRF system, we have chosen to use a solid-state RF power amplifier (SSPA). This presentation highlights the design results of the RF system for the Korea 4GSR, as well as prototypes of the 3rd harmonic cavity and SSPA.

The adoption of Solid State Power Amplifier (SSPA) is rapidly increasing in major accelerators worldwide, replacing tube amplifiers such as Klystron and IoT. This study aimed to develop a High-Power RF system for Multipurpose Synchrotron Radiation Accelerators and to design and implement a GaN transistor-based SSPA. Through this research, we verified control performance equivalent to that of a 150 kW SSPA and successfully developed a prototype of a 5 kW RF module. Experimental results confirmed that the GaN transistor-based SSPA provides high efficiency and stable performance in the 500 MHz band, and based on this, we established a performance assurance plan for the 150 kW SSPA. This study demonstrates that GaN devices can effectively replace LDMOS devices with similar performance and competitiveness in the RF applications operating in the 500 MHz frequency range, which has traditionally been dominated by LDMOS. These results have significant implications for enhancing the performance and efficiency of High-Power RF systems and are expected to greatly expand the potential applications of GaN-based SSPA in various scientific and industrial research fields.