SEQUOIA: A Newly Operating Chopper Spectrometer at the SNS

TLDR

SEQUOIA, a fine‑resolution chopper spectrometer, recently received its first neutrons at the SNS. The instrument’s commissioning phase is currently underway. SEQUOIA uses neutrons with incident energies between 10–2000 meV, delivers a monochromatic beam via a Fermi chopper 18 m from the source, and detects scattered neutrons with a 3He linear position‑sensitive tube array on a 5.5‑m radius vertical cylinder. Current commissioning results show that SEQUOIA’s actual performance matches predictions from analytical calculations and Monte Carlo simulations.

Abstract

A fine resolution chopper spectrometer (SEQUOIA) recently received first neutrons at the SNS. The commissioning phase of the instrument is underway. SEQUOIA is designed to utilize neutrons of an incident energy (Ei) between 10-2000 meV. A monochromatic beam is provided on a sample, 20 m from the decoupled ambient temperature H2O moderator, by filtering the white beam with a Fermi chopper located 18 m from the source. After interacting with the sample, neutrons are detected by an array of 3He linear position sensitive tubes located on a vertical cylinder with a radius of 5.5 m. This contribution presents current results from the commissioning experiments and compares SEQUOIA's actual and predicted performance. These commissioning experiments include characterization of the beam by monitors, determination of the chopper phase offsets, and runs with V and C4H2I2S. The predicted performance is provided by analytical calculations and Monte Carlo simulations.