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TOPAS (under construction)
Thermal time-of-flight spectrometer with polarization analysis
TOPAS will be a thermal time of flight spectrometer featuring polarization analysis. It is optimized for high flux and good energy resolution.
It features a 45 m elliptic neutron guide, which focuses the neutrons onto the sample in the new eastern neutron guide hall. The guide is designed to provide an intense neutron beam at the sample, and to keep the background low, which can arrive in the experimental area.
A beam stop at the centre of the ellipse blocks the direct line of sight to the reactor and a small
The chopper system consists of two Fermi choppers, which provide very short neutron pulses even for large neutron windows, which are a consequence of the elliptic neutron guide. We emphasize, that the Fermi choppers also provide high repetition rates up to
An additional disk chopper removes contamination pulses of unwanted neutron velocities.
The neutron beam can be polarized by a continuously operated spin exchange optical pumping 3He filter cell, which provides a constant polarization efficiency.
The final choppers and the flight path volume haven’t any window to keep parasitic scattering low. The vacuum system is designed to reach cryogenic vacuum to allow low temperature applications without additional neutron windows. The volume around the sample can be separated from the rest of the flight path volume for the exchange of the sample or sample environment.
The sample can be rotated by 360º to map the full dispersion relation in single crystalline materials.
The TOPAS detector consists of 289
By the use of thermal neutrons, a large range in energy and momentum transfer can be probed. In the direct time-of-flight geometry, the measurement of the momentum transfer is decoupled from the measurement of the energy transfer.
Time-of-flight spectroscopy from single crystals explores simultaneously the Q, ω space and maps a variety of excitations by covering a large solid angle with detectors.
Accordingly, TOPAS can be used for a wide range of applications, particularly for novel materials:
For many of the intended instrument applications polarization analysis will provide unique opportunities e.g. for the study of magnetic excitations or the separation of the spin incoherent scattering in hydrogen containing materials.