Speaker
Description
The cold neutron direct geometry inelastic spectrometer(CNIS) is one of the planned instruments for the CSNS-II project. The scattering chamber, located at the instrument's end, features a semi‑fan shape covering an angular range of –30° to 138°, with a volume of ~75 m³, a height of ~4 m, and is made of stainless steel. The chamber provides interface for sample environment, supports installation of 1‑inch ³He tubes (3 m length), and maintains a high‑vacuum, low‑background environment at 5×10⁻³ Pa. Detectors operate in “airbox” mode: high‑voltage interfaces, preamplifiers, and digital circuit boards are housed in airtight boxes, connected externally via bellows; the tube high voltage is independent of chamber vacuum. Inside, 12 detector support bases (each accommodating 4 detector units, each unit containing 8 ³He tubes) and one circular guide rail are installed. A maintenance carriage on the rail rotates around the centre to facilitate installation and removal of detector units. Four DN400 top flanges allow crane‑assisted handling of detector units. Eleven isolating plates are mounted between the detector support bases. The detailed design is complete, and the chamber is currently under fabrication. This abstract presents the structural design, detector maintenance procedures, and vacuum system rationale.
Key Words
CNIS, Scattering chamber, Vacuum system, ³He detector, airbox, maintainability