RF Simulation and Testing for HALF 499.8 MHz Higher-Order-Mode Absorber Prototypes

In modern particle accelerators, Beam Line higherorder mode Absorber (BLA) has been successfully employed in storage ring cavities to cope with high average beam current. Two BLAs with different microwave absorbing material and cooling structure have been designed and fabricated during the Hefei Advanced Light Facility (HALF) pre-research period. In this paper, the microwave design, the absorptance and the vacuum test of the two absorbers were presented. The test results show that the TEM mode absorptance of the two BLAs are better than 40% and 55% in the frequency range of 0.6 to 3 GHz and 0.8 to 1.5 GHz, respectively. Especially, the hybrid BLA reached $\mathbf{8 0 \%}$ in the frequency range of 1.25 to 1.8 GHz. The ultimate vacuum of the ferrite BLA were tested $3.7 * 10^{-10}$ mbar and the hybrid BLA $4.6 * 10^{-10} \mathrm{mbar}$. Design specifications has been satisfied.