Ion-Optical Tuning of the Large Acceptance Spectrometer for Improved Angular Resolution and Acceptance

TL;DR

This paper evaluates how ion-optical tuning of the Large Acceptance Spectrometer affects angular resolution and acceptance, demonstrating a trade-off influenced by magnet field strength and focusing adjustments.

Contribution

It provides a quantitative analysis of the resolution-acceptance trade-off in LAS and explores how magnetic field strength and focusing impact spectrometer performance.

Findings

Resolution improves with increased field strength, reaching about 5.5 mrad at +20%.

Stronger fields decrease acceptance and solid angle.

Enhanced focusing allows high-precision angle reconstruction.

Abstract

The trade-off between angular resolution and acceptance in scattering-angle measurements with a magnetic spectrometer is quantitatively evaluated for the Large Acceptance Spectrometer (LAS). The dependence on the multipole magnet field strength is investigated. Third-order transfer matrices were calculated with GICOSY, and particle transport was simulated with MOCADI. The vertical angular resolution is defined as the standard deviation between reconstructed and true angles, while the acceptance is determined from the transport efficiency within an elliptical gate in target angle space. The resolution improves with increasing field strength, reaching $\sigma_b \sim 5.5$ mrad at +20\%, consistent with $5.43 \pm 0.20$ mrad. In contrast, stronger fields reduce the vertical acceptance and solid angle. These results demonstrate a trade-off between resolution and acceptance. Enhanced vertical focusing shifts the focal condition away from the nominal focal plane, enabling high-precision reconstruction.