Development of high-power vacuum dry RF loads in IHEP

Purpose In Linacs, achieving higher accelerating gradients inevitably demands higher-power RF sources and RF loads. These loads are crucial for absorbing the residual RF power. While IHEP has developed a series of SiC dry loads covering several frequency bands, their peak power capacity is limited to only several tens of megawatts. Therefore, this paper presents the development and proposal of pure stainless steel loads that are capable of withstanding power levels in the hundreds of megawatts range.
Methods Simulations and optimizations of the pure stainless steel load were conducted in CST with the aim of attaining lower input reflection and a broader operating frequency band. Low-power RF tests and high-power conditioning were carried out to verify the design.
Results The length of the pure stainless steel load was optimized, and it was ultimately reduced to less than 1 m. Throughout the processes of fabrication, welding and high-power conditioning, the load achieved a VSWR of less than 1.1 at the operating frequency and a bandwidth of over 100 MHz (with S₁₁ < -20.0 dB). During the high-power conditioning stage, the load operated stably at a peak power of 177.8 MW.
Conclusions This paper comprehensively details the design, simulation, fabrication, cold test, and high-power conditioning of all-metal loads. The obtained results are satisfactory, demonstrating that the loads exhibit strong absorption and thermal stability during high-power conditioning.