Analyzing the effects of post couplers in DTL tuning by the equivalent circuit model

TL;DR

This paper uses an equivalent circuit model to analyze how post couplers stabilize the accelerating field in Drift Tube Linacs, revealing the relationship between frequency errors and field sensitivity, and comparing symmetrical and asymmetrical PCs.

Contribution

It introduces a circuit model for asymmetrical post couplers and demonstrates their effect on field stabilization and distribution in DTLs.

Findings

Field sensitivity is proportional to √(δω/ω₀) without PCs.

Field sensitivity is proportional to δω/ω₀ with PCs.

Asymmetrical PCs have similar stabilization effects as symmetrical ones.

Abstract

Stabilization of the accelerating field in Drift Tube Linac(DTL) is obtained by inserting Post Couplers(PCs).On the basis of the circuit model equivalent for the DTL with and without asymmetrical PCs, stabilization is deduced quantitatively: let $\delta \omega/\omega_0$ be the relative frequency error, then we discover that the sensitivity of field to perturbation is proportional to $\sqrt{\delta \omega / \omega_0}$ without PCs and to $\delta \omega/\omega_0$ with PCs. Then we adapt the circuit model of symmetrical PCs for the case of asymmetrical PCs. The circuit model shows how the slope of field distribution is changed by rotating the asymmetrical PCs and illustrates that the asymmetrical PCs have the same effect as the symmetrical ones in stabilization.