Experimental investigation of pulsed gallium nitride solid-state power amplifier for the China Spallation Neutron Source Phase II linac

In the Phase II upgrade of the China Spallation Neutron Source, the linac system will achieve a beam energy upgrade from 80 to 300 MeV through the implementation of twenty 324 MHz spoke superconducting radio frequency (SRF) cavities and twenty-four 648 MHz elliptical SRF cavities. Each spoke cavity requires a dedicated solid-state power amplifier (SSPA) delivering 300 kW peak RF power at a pulse width of 1.2 ms and a repetition rate of 50 Hz. This paper presents the development and experimental validation of a novel pulsed GaN (Gallium Nitride) based SSPA system that employs high-power GaN HEMTs (high-electron-mobility transistors), a redundant direct-current supply subsystem, a compact power-combining network, and a modular architecture. The first prototype SSPA has been successfully built and tested. Measurement results demonstrate that the GaN-based PA modules provide 130% higher output power than conventional laterally diffused metal–oxide–semiconductor (LDMOS) technology at 324 MHz, thereby reducing the number of required amplifier units by 50% while maintaining sufficient power margin. The system exhibits excellent reliability, availability, and operational flexibility, meeting all design specifications.