Introduction

The S800 1) is a superconducting spectrograph used for reaction studies with high-energy radioactive beams produced at the NSCL Coupled-Cyclotron Facility (CCF) and the A1900 Separator 2). It was designed for high-precision measurements of scattering angles (ΔΘ=2 msr) and momentum (p/Δp=2×104), and large momentum and solid-angle acceptances (ΔΩ=20 msr, Δp/p=6%). The S800 layout shown in the next figure depicts the two parts of the S800: the analysis line and the spectrograph.

Layout of the S800

Analysis Line

The analysis line extends from the object position to the target station, with a total length of 22 m. It includes four 22.5° dipoles, five quadrupole triplets, and two vertically steering magnets, assembled in two segments with configurations QQQ-H-DD-QQQ (segment 6) and QQQ-DD-H-QQQ-QQQ (segment 7) symmetrically oriented around an intermediate image plane. The maximum rigidity is 5 Tm, although it depends on the tune of the quadrupoles. The acceptances of the analysis line depends on the optical mode. The sequence of pictures below include the object-box station at the “entrance” of the analysis line (left, top); section following the object station in front of the first pair of dipoles (right, top); section around the intermediate image station between the two pairs of dipoles (left, bottom); and the section following the intermediate image section with the last dipole of the second pair shown (right, bottom).

Object-station box (western side of top level of the of S3 vault). Section of analysis line following the object station (western side of top level of the of S3 vault). Section of analysis line covering the intermediate-image station (stairs connecting the middle level and the western side of the top level of the of S3 vault). Section of analysis line following the intermediate-image station (bottom level of the S3 vault).

Spectrograph

The spectrograph consist of two quadrupoles, a sextupole and two big dipoles assembled in a QQ-S-DD configuration (segment 8) that spans vertically from the target station to the focal plane, with a total length of 18 m. The sequence of pictures below show the quadrupole doublet at the “entrance” of the spectrograph (left); the side view of the spectrograph as seen from the south bottom level of the S3 vault; and the second dipole as seen from the top level.

Spectrograph quadrupole doublet (yellow chamber) as seen from the bottom of the S3 vault. Spectrograph as seen from the south bottom of the S3 vault. Note that only the second dipole can be seen. Second dipole of the spectrograph as seen from the top of the S3 vault.

The figures of merit of the spectrograph are summarized in the next table and figure below. Achieving the nominal angle and momentum resolution require the control of different conditions such as object size (less than 0.5 mm), target thickness, uncertainty of the incident angle on the target, intensity, and whether or not the incoming beam needs to be tracked.

Momentum Resolution (p/Δp) 2×104
Momentum Acceptance 5.8%
Angle Resolution 2 msr
Solid Angle Acceptance 7º×10º or 20 msr
Momentum Dispersion (x/δ) 9.5 cm/%
Angle Dispersion (y/b) 0.9 mm/mrad
Magnification(x/x) 0.74
Focal Plane Size (x × y) 55 cm ×15 cm
Maximum Rigidity 4 Tm
Detector Position Resolution (x) 0.3 mm
Detector Position Resolution (y) 0.3 mm
Weight 250 tons
Length Analysis Line 22 m
Length Spectrograph 18 m

Energy and Angle resolutions of S800

1)
D. Bazin, J.A. Caggiano, B.M. Sherrill, J. Yurkon, and A. Zeller, Nuclear Instruments and Methods in Physics Research B 204, 629 (2003)
2)
D.J. Morrissey, B.M. Sherrill, M. Steiner, A. Stolz, and I. Wiedenhoever, Nuclear Instruments and Methods in Physics Research B 204, 90 (2003)