BTF measurements with beam-beam interactions

TL;DR

This paper investigates the transverse beam transfer function (BTF) of particle beams affected by beam-beam interactions and Gaussian electron lenses, using simulations and analytic models to understand and quantify these effects.

Contribution

It extends BTF formalism to include electron lens effects and compares analytic predictions with PIC simulations for beam-beam interactions under split tune conditions.

Findings

The analytic BTF model accurately describes the electron lens influence.

PIC simulations confirm the validity of the formalism under certain conditions.

The formalism can estimate electron lens strength through fitting procedures.

Abstract

We present considerations about the transverse beam transfer function (BTF) of beams under the influence of two effects: The strong-strong beam-beam effect and the influence of a Gaussian electron lens. The BTF are investigated using two methods: BTF excitation is simulated in a particle-in-cell (PIC) code. The BTF model is verified using a known analytic expectation. Analytic expectations for BTF of beams under a stationary electron lens are derived by extending BTF from the formalism of Berg and Ruggiero. Finally we compare the analytic BTF results for a stationary Gaussian lens to both the PIC simulation for split tune conditions and to PIC simulations for a beam influenced by an electron lens. We conclude that the formalism represents the electron lens well and can be applied to a limited extend to the beam-beam effect under split tune conditions. The analytic formalism allows us to recover the strength of an electron lens by means of fitting and can give clues regarding the strength of the beam-beam effect under split tune conditions.