The research work of Hefei Advanced Light Facility (HALF) is
in progress. A 499.8 MHz superconducting cavity will be used in the
HALF RF system. The preliminary RF design and thermal analysis for
the fundamental power coupler (FPC) of HALF 499.8 MHz
superconducting cavity have been completed. Multipacting (MP) is one
of the major causes of the breakdown in many high power input
couplers and RF cavities, thus, MP simulation for our FPC is
necessary. In this paper, the MP simulation for the FPC was
performed by using the CST. The MP performance of the FPC was
studied. The formation process of the MP in the FPC was investigated
and the physical mechanism of the delay of the MP establishment was
analyzed. The simulation results show that MP will occur when the
power level is higher than 175 kW, and the MP location is near the
ceramic. Therefore, MP suppression is required in the FPC. In order
to suppress the MP, the effect of the biasing DC electric voltage to
MP in the FPC was analyzed in this paper. The simulation results
indicates that the biasing DC electric voltage not only can suppress
the MP, but also can excites new MP in the coupler. Thus, it is
crucial to select the appropriate biasing DC electric voltage for
the MP suppression in the coupler. The results show that the MP in
the FPC can be suppressed very well by using 2 kV or 3 kV biasing
DC electric voltage.