Optimization of multi-gap extended output cavity for a G-band sheet beam extended interaction klystron

For a G-band sheet beam extended interaction klystron (SBEIK), an eight-gap extended output cavity that operates in the 2π mode, is optimized by using an equivalent method, in which the external load is replaced by a lossy region in 3D particle-in-cell model. The optimized eight-gap extended output cavity has 681.9 unloaded Q, 952 external Q and 397.3 loaded Q at 220 GHz. The simulations based on the prebunched sheet beam predict that the output power and bandwidth of the eight-gap extended output cavity are larger than 600 W and 200 MHz, respectively. It is efficient for rapidly designing the G-band SBEIK.