# Proposal for VEPP-4M beam energy measurement using magnetic spectrometer with Compton calibration and photon detector

## TL;DR

This paper proposes a novel method for measuring beam energy in circular accelerators using a magnetic spectrometer calibrated with Compton backscattering and photon detection, promising high accuracy with minimal setup.

## Contribution

It introduces a new technique combining magnetic spectrometry and Compton calibration for precise beam energy measurement in circular accelerators.

## Key findings

- Expected measurement uncertainty better than 10^-4
- Method can be implemented with minimal effort on existing equipment
- Calibration using two laser wavelengths enhances accuracy

## Abstract

A method for circular e$^-$/e$^+$ accelerator beam energy measurement is proposed. Coordinate of an electron (or a positron) in a focusing magnetic spectrometer built in a circular accelerator depends on its energy, two spectrometer parameters, and the circulating beam energy. The spectrometer parameters can be defined using minimum electron energies from Compton backscattering with two laser wavelengths, and an additional photon coordinate detector. The photon detector is calibrated at once at well-known beam energy. The VEPP-4M collider has appropriate equipment for the method implementation: built-in focusing magnetic spectrometer, Compton calibration system with two lasers and a photon coordinate detector. Thus, the proposed technique could be implemented with minimum efforts; tests and further upgrade are planned. The beam energy can be defined with expected uncertainty better than $10^{-4}$.