• X.C. Wang, L.G. Shen, Z. Shu, Y. Sun
  USTC/PMPI, Hefei, Anhui
• K. Jin, Y.J. Pei
  USTC/NSRL, Hefei, Anhui

Microwave-absorbing material is an essential part of LINAC collinear load. It is coated on the inner walls of several trailing accelerating cavities to transform the remnant microwave power into heat. Fe-85%Si-9.6%Al-5.4% alloy, which reveals low outgassing rate and high attenuation, is selected for collinear load R&D. To measure the permittivity and permeability of FeSiAl at 2856 MHz, the coaxial transmission-reflection method is adopted. The system is firstly examined by testing the hollow coaxial fixture and comparing the results with the electromagnetic parameters of the air. Measurements of two PTFE rings show that the air gaps between the fixture and samples influence the test results seriously. CST is utilized to simulate the effects on the FeSiAl measure-ments. Eventually a scheme of molding the samples of FeSiAl powder mixed with paraffin to form a wax mold is proposed and the permittivity and permeability of FeSiAl are derived from the electromagnetic parameters equivalent formulas of mixed medium.

• C.-F. Wu, H. Fan, W. Fan, G. Feng, W.W. Gao, K. Jin, W. Li, G. Liu, L. Wang, S.C. Zhang, Y. Zhao
  USTC/NSRL, Hefei, Anhui
• R.A. Bosch
  UW-Madison/SRC, Madison, Wisconsin

A radio frequency system with a higher-harmonic cavity will be used to increase the beam lifetime and suppress coupled-bunch instabilities of the upgrade Hefei Light Source. In the paper, the simulated results confirm that tuning in the harmonic cavity may suppresses the parasitic coupled-bunch instabilities. The higher-harmonic cavity has been designed and the calculated optimum lifetime increase ratio is 2.58.