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

Taichi Miyagawa; Junki Tanaka; Shinsuke Ota; Masanori Dozono; Nobuyuki Kobayashi; Lakmin Wickremasinghe; Fumiya Furukawa; Daichi Ishii; Sho Nishioka; Kota Takahashi; Erika Ukai

arXiv · 2605.08127

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

Taichi Miyagawa·Junki Tanaka·Shinsuke Ota·Masanori Dozono·Nobuyuki Kobayashi·Lakmin Wickremasinghe·Fumiya Furukawa·Daichi Ishii·Sho Nishioka·Kota Takahashi·Erika Ukai

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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.

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Taichi Miyagawa, Junki Tanaka, Shinsuke Ota, Masanori Dozono, Nobuyuki Kobayashi, Lakmin Wickremasinghe, Fumiya Furukawa, Daichi Ishii, Sho Nishioka, Kota Takahashi, Erika Ukai. 2026-04-30. Ion-Optical Tuning of the Large Acceptance Spectrometer for Improved Angular Resolution and Acceptance. https://arxiv.org/abs/2605.08127

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