Modeling of a passive fourth harmonic cavity for the Hefei Light Source upgrade HLSII

Abstract

The use of a fourth-harmonic cavity is studied for the planned upgrade of the 800-MeV Hefei Light Source HLSII. Analytic modeling and simulations indicate that such a cavity can successfully suppress parasitic coupled bunch instabilities and lengthen the bunch by a factor of 2.6. For optimally lengthened bunches, the microwave instability is not expected for broadband impedances of 2 ohms or less. The modeling suggests that a fourth-harmonic cavity may be successfully used at HLSII.