Effect of transverse electron velocities on the longitudinal cooling force in the Fermilab electron cooler

TL;DR

This paper investigates how transverse electron velocities, induced by magnetic field adjustments, affect the longitudinal cooling force in Fermilab's electron cooler, comparing measurements with theoretical models.

Contribution

It introduces a model that accounts for the impact of helix-like electron trajectories on the cooling force, highlighting the effects of transverse velocities.

Findings

Qualitative agreement between measurements and the model.

Helical trajectories influence the cooling force.

Magnetic field adjustments can modify electron trajectories.

Abstract

In Fermilab's electron cooler, a 0.1A, 4.3MeV DC electron beam propagates through the 20 m cooling section, which is immersed in a weak longitudinal magnetic field. A proper adjustment of 200 dipole coils, installed in the cooling section for correction of the magnetic field imperfections, can create a helix-like trajectory with the wavelength of 1-10 m. The longitudinal cooling force is measured in the presence of such helixes at different wavelengths and amplitudes. The results are compared with a model calculating the cooling force as a sum of collisions with small impact parameters, where the helical nature of the coherent angle is ignored, and far collisions, where the effect of the coherent motion is neglected. A qualitative agreement is found.