Field Stabilization of Alvarez-Type Cavities

TL;DR

This paper introduces a novel method for stabilizing the electromagnetic field in Alvarez-type cavities by optimizing stem configurations, eliminating the need for post-couplers and enhancing field homogeneity and robustness.

Contribution

It proposes using the cavity stems' azimuthal orientations as adjustable parameters to improve field stability, supported by analytical and simulation-based optimization.

Findings

Achieves flat field distributions without post-couplers

Reduces field tilt sensitivities significantly

Provides a systematic approach for cavity field optimization

Abstract

Alvarez-type cavities are commonly used to reliably accelerate high quality hadron beams. Optimization of their longitudinal field homogeneity is usually accomplished by post-couplers, i.e. additional rods being integrated into the cavity. This paper instead proposes to use the stems that keep the drift tubes for that purpose. As their individual azimuthal orientations do not change the cavity's undisturbed operational mode, they comprise a set of free parameters that can be used to modify higher mode field patterns. The latter have significant impact on the robustness of the operational mode w.r.t. eventual perturbations. Several optimized stem configurations are presented and benchmarked against each other. The path to obtain these configurations is paved analytically and worked out in detail through simulations. It is shown that the method provides for flat field distributions and very low field tilt sensitivities without insertion of post-couplers.