SPHERES is a third-generation neutronbackscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Jülich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 μeV, a dynamic range of ± 31 μeV, and a signal-to-noise ratio of up to 1750:1.
Building and commissioning SPHERES has been funded by the German Bundesministerium für Bildung und Forschung (Project Nos. 05NX8CJ1 and 03RI16JU1). Foundations for SPHERES were laid by former project scientists Oliver Kirstein and Peter Rottländer, and by former project engineer Tadeusz Kozielewski. Many other colleagues from the Forschungszentrum Jülich contributed to this project. We would like to acknowledge Ulrich Probst, Helga Straatmann, and Thomas Koppitz for the development of the chopper rotor, Ulrich Giesen and Ulrich Pabst for a vibrational analysis thereof, Christoph Tiemann for his contribution to the Doppler drive, Gerd Schaffrath for the instrument housing, Manfred Bednarek for the electrical installations, Peter Stronciwilk and Marco Gödel for mechanical constructions, Vu Thanh Nguyen for the accurate gluing of the silicon crystals, Harald Kusche, Andreas Nebel, and Björn Poschen for technical support, and Alexander Ioffe for coordinating the JCNS outstation at FRM II. Sergej Manoshin and Alexander Ioffe contributed a simulation of the convergent neutron guide. Michaela Zamponi, the new instrument responsible since fall 2011, contributed to the last Au activation measurement.
We are grateful to Winfried Petry, Jürgen Neuhaus, and all the staff of FRM II for their hospitality. We thank Harald Türck for generous help at all levels of engineering, Christian Breunig for the neutron guide, Philipp Jüttner for the shutter construction, Helmut Zeising, Birgit Wierczinski, and their entire team for the smooth handling of the radioprotection necessities, and Ralf Lorenz for sensibly supervising our safety. We thank our colleagues and friendly concurrents Bernhard Frick, Tilo Seydel, and Lambert van Eijck of the ILL for stimulating discussions and the open exchange of experiences and ideas. Victoria García Sakai, Goran Gasparovic, and Dan A. Neumann kindly showed us HFBS at NIST, and Andreas Meyer provided insights from his commissioning experience.
I. INTRODUCTION II. INSTRUMENT DESIGN A. Instrument layout B. Crystal choices C. Time-of-flight logic III. INSTRUMENT COMPONENTS A. Neutron guide and velocity selector B. Phase-space transform chopper C. Monochromator and analyzers D. Monochromatordoppler drive E. Backscatteringdetectors F. Diffraction detectors G. Instrument housing with argon filling H. Sample environments IV. INSTRUMENT CONTROL AND DATA ACQUISITION A. High-level user interface B. Instrument-control daemons C. Spectral acquisition electronics D. Spectral acquisition daemon E. Safety instrumentation and slow control V. DATA PROCESSING A. Raw-data postprocessor B. Raw-data reduction with SLAW C. Instead of a monitor VI. PERFORMANCE A. Flux and count rates B. Dark counts C. Chopper modulation of count rates D. Resolution and signal-to-noise ratio VII. COMPARATIVE STATUS AND PERSPECTIVE