Transverse instability of the antiproton beam in the Recycler Ring

TL;DR

This paper investigates the transverse instability limiting antiproton beam brightness in Fermilab's Recycler Ring, introducing a threshold phase density concept and confirming it aligns with a resistive wall instability model.

Contribution

It introduces the threshold phase density for beam stability and demonstrates its agreement with a resistive wall instability model in the Recycler Ring.

Findings

Threshold phase density characterizes beam stability.

Reducing RF potential well depth lowers the instability threshold.

Observed features match resistive wall instability predictions.

Abstract

The brightness of the antiproton beam in Fermilab's 8 GeV Recycler ring is limited by a transverse instability. This instability has occurred during the extraction process to the Tevatron for large stacks of antiprotons even with dampers in operation. This paper describes observed features of the instability, introduces the threshold phase density to characterize the beam stability, and finds the results to be in agreement with a resistive wall instability model. Effective exclusion of the longitudinal tails from Landau damping by decreasing the depth of the RF potential well is observed to lower the threshold density by up to a factor of two.