Electron Cloud Buildup Characterization Using Shielded Pickup Measurements and Custom Modeling Code at CESRTA

TL;DR

This study combines shielded pickup measurements and custom ECLOUD modeling to analyze electron cloud buildup in CESRTA, revealing sensitivities to photoelectron and secondary emission parameters across different chamber coatings and beam conditions.

Contribution

It introduces a detailed measurement approach with shielded pickups and applies a specialized ECLOUD model to understand electron cloud dynamics in various chamber coatings.

Findings

Measurements are sensitive to photoelectron energy and azimuthal distributions.

Secondary yield parameters significantly influence cloud buildup.

Results vary with chamber coating and beam parameters.

Abstract

The Cornell Electron Storage Ring Test Accelerator experimental program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1-m-long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. They detect cloud electrons migrating through an 18-mm-diameter pattern of small holes in the top of the chamber. A digitizing oscilloscope is used to record the signals, providing time-resolved information on cloud development. Carbon-coated, TiN-coated and uncoated aluminum chambers have been tested. Electron and positron beams of 2.1, 4.0 and 5.3 GeV with a variety of bunch populations and spacings in steps of 4 and 14 ns have been used. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to the physical phenomena determining cloud buildup such as the photoelectron production azimuthal and energy distributions, and the secondary yield parameters including the true secondary, re-diffused, and elastic yield values.