Effect of secondary ions on the electron beam optics in the Recycler Electron Cooler

TL;DR

This paper investigates how secondary ions influence electron beam optics in Fermilab's Recycler Electron Cooler, demonstrating that ion removal significantly improves cooling efficiency by nearly doubling the longitudinal cooling rate.

Contribution

It introduces a method to clear ions from the electron beam and analyzes its impact on beam optics and cooling performance.

Findings

Ion removal doubles the longitudinal cooling rate.

Accumulated ions significantly degrade beam optics.

Interrupting the beam effectively clears ions.

Abstract

Antiprotons in Fermilab's Recycler ring are cooled by a 4.3 MeV, 0.1 - 0.5 A DC electron beam (as well as by a stochastic cooling system). The unique combination of the relativistic energy ({\gamma} = 9.49), an Ampere - range DC beam, and a relatively weak focusing makes the cooling efficiency particularly sensitive to ion neutralization. A capability to clear ions was recently implemented by way of interrupting the electron beam for 1-30 \mus with a repetition rate of up to 40 Hz. The cooling properties of the electron beam were analyzed with drag rate measurements and showed that accumulated ions significantly affect the beam optics. For a beam current of 0.3 A, the longitudinal cooling rate was increased by factor of ~2 when ions were removed.