# Measurement of the Spin Tune Using the Coherent Spin Motion of Polarized Proton in a Storage Ring

## TL;DR

This paper introduces a method to precisely measure the spin tune of polarized protons at high energies using driven coherent spin motion, enabling better polarization control in proton colliders.

## Contribution

It demonstrates the first high-energy spin tune measurement using driven coherent spin motion with a spin flipper and turn-by-turn polarization measurement.

## Key findings

- Successful measurement at 24 GeV and 255 GeV energies.
- High spin-flip efficiency demonstrated with a nine-magnet spin flipper.
- Measurement preserves polarization, enabling in-operation spin tune determination.

## Abstract

This paper reports the first spin tune measurement at high energies (24 GeV and 255 GeV) with a driven coherent spin motion. To maintain polarization in a polarized proton collider, it is important to know the spin tune of the polarized proton beam, which is defined as the number of full spin precessions per revolution. A nine-magnet spin flipper has demonstrated high spin-flip efficiency in the presence of two Siberian snakes [1]. The spin flipper drives a spin resonance with a given frequency (or tune) and strength. When the drive tune is close to the spin tune, the proton spin direction is not vertical anymore, but precesses around the vertical direction. By measuring the precession frequency of the horizontal component the spin tune can be precisely measured. A driven coherent spin motion and fast turn-by-turn polarization measurement are keys to the measurement. The vertical spin direction is restored after turning the spin flipper off and the polarization value is not affected by the measurement. The fact that this manipulation preserves the polarization makes it possible to measure the spin tune during operation of a high energy accelerator.