Four-dimensional emittance measurement at the Spallation Neutron Source

TL;DR

This paper develops and tests methods to measure the four-dimensional emittance of a hadron beam in the SNS ring, enabling better control and optimization of beam properties for improved accelerator performance.

Contribution

It introduces a variant of the multi-optics method and modifications to the wire-scanner region to accurately measure 4D emittance during accumulation.

Findings

Successful implementation of the multi-optics method with wire-scanners.

Modified wire-scanner region reduces uncertainty in fixed-optics measurements.

Demonstrated 4D emittance evolution during beam accumulation.

Abstract

A coasting hadron beam with an elliptical transverse profile, uniform charge density, and small transverse four-dimensional (4D) emittance could improve accelerator performance in several contexts. A phase space painting method to generate such a distribution is being tested in the Spallation Neutron Source (SNS) accumulator ring. A critical component of these efforts is to measure the 4D emittance of the beam during accumulation. The 4D emittance can be reconstructed from measured beam profiles in two ways: in the multi-optics method, the optics between a reconstruction and measurement location are varied; in the fixed-optics method, multiple measurement locations are used without modifying the optics. The fixed-optics method is faster but can lead to large uncertainty in the reconstructed 4D emittance. In this paper, we implement a variant of the multi-optics method using the four available wire-scanners near the SNS target. We also modify the wire-scanner region to reduce the uncertainty of the fixed-optics method. We then demonstrate the usefulness of the fixed-optics method by reconstructing the 4D emittance evolution during accumulation in the SNS ring.