Equivalent circuit model for stability modulation in Drift Tube Linac

Drift tube linac (DTL) uses the post coupler structure to achieve field stability. In order to explain the mechanism of stability modulation, we explained the structure of the DTL, then, we used the equivalent circuit model to analyse the structure and listed the circuit diagram. At last, we paid attention to the equivalent capacitance which represents the effect between post coupler and drift tube, and made its simulation. The circuit model was used to analyse the disturbed field and provide an explanation of post coupler stabilization. Through comparing the post coupler capacitances from simulation and circuit model, we got the reasonable width of the gap between post coupler and drift tube. Finally, we simulated the disturbed field under different conditions and the circuit theory was confirmed. (authors)