Coil Creep and Skew-Quadrupole Field Components in the Tevatron

TL;DR

This paper investigates the causes of strong beam coupling in the Fermilab Tevatron, identifying coil displacement in superconducting dipoles as a key factor and demonstrating how in situ adjustments improved performance.

Contribution

It reveals that coil displacement in superconducting dipoles causes skew quadrupole fields, and shows how in situ corrections enhance collider operation.

Findings

Coil displacement in dipoles causes skew quadrupole fields.

Adjustments of magnets improved Tevatron performance.

Strong coupling was linked to coil displacement and was mitigated by in situ corrections.

Abstract

During the first 20 years of operation, the Fermilab Tevatron developed strong coupling between the two transverse degrees of freedom. The required strength of the circuit of skew quadrupole magnets used to correct for coupling, though capable, had increased by an order of magnitude since 1983. Changes made to the Tevatron for colliding beams operation had altered the skew quadrupole corrector distribution and strong coupling became evident, often encumbering routine operation during the colliding beam physics run. It was discovered that the superconducting coils of the main dipole magnets had become vertically displaced relative to their yokes since their construction. The ensuing systematic skew quadrupole field introduced by this displacement accounts for the required corrector settings and observed beam behavior. The magnets were adjusted in situ over the course of several long maintenance periods and the Tevatron performance improved as a result.