Tuning of Multicell Superconducting Accelerating Cavities using Pressurized Balloons

TL;DR

This paper introduces a novel, non-invasive, and cost-effective method using pressurized balloons to locally tune dressed multicell superconducting cavities, demonstrated on a 9-cell 1.3 GHz cavity.

Contribution

It presents a new balloon-based tuning technique for jacketed cavities that avoids cutting the vessel, improving efficiency and reducing costs.

Findings

Successfully tuned a 9-cell 1.3 GHz cavity using the method.

The technique allows localized deformation without disassembling the cavity.

The method is applicable to dressed superconducting cavities in accelerator development.

Abstract

Plastic tuning of multicell superconducting accelerating cavities is crucial in the development cycle of cavities for particle accelerators. Cavities must meet stringent requirements regarding the operating mode frequency, field flatness, and eccentricity before lining them up in a cryomodule string. After dressing bare cavities with helium vessels, the welded vessel prevents access to individual cavity cells disallowing any further localized tuning. Currently, there is no straightforward way to tune dressed cavities other than cutting the vessel and then tuning the bare cavity and dressing it back, which would significantly impact cost and schedule. In this paper, we present a novel tuning technique for already jacketed cavities that is non-invasive and cost-effective. The proposed scheme employs pressurized balloons to be temporarily deployed inside the cavity as a means to localize mechanical deformation in specific cells. The proposed tuning technique was successfully utilized to recover a 9-cell 1.3 GHz tesla-style cavity.