PUMA

Insrumentscheme PUMA

Three axes spectrometers allow the direct measurement of the scattering function S(Q, ω) in single crystals at well-defined points of the reciprocal lattice vector Q and frequency ω and thus represent the most general instrument type.

PUMA is characterised by a very high neutron flux as a result of the efficient use of focussing techniques. Three different vertical openings and a horizontal slit with a maximum opening of 40 mm define the virtual source, which is two metres before the monochromator. To reduce the primary beam’s contamination by epithermal neutrons, a sapphire filter can be placed in front of the monochromator. PUMA has a remote controlled monochromator changing unit, which allows placing of one out of four different monochromators PG(002), Cu(220), Cu(111), Ge(311) inside the drum. High-precision mechanical couplings for mounting the individual monochromators on the monochromator table ensure optimum adjustment after the monochromator change without additional readjustment. All monochromators are equipped with double focussing devices that allow optimum focussing conditions over a wide range of incident wavevectors ki.

On the secondary spectrometer, PG(002) and Ge(311) analysers are also available with a focussing option. The horizontal divergence of the beam can be defined using a series of four Soller collimators. The two inside the drum, before and after the monochromator, can be changed remotely, whereas the two in the analyser housing can be changed manually. The orientation of the sample can be checked using a tilt and translation goniometer (+/- 20°, +/- 12 mm). This has a load capacity of up to one ton and allows the use of heavy sample environments. Alternatively, an Euler cradle with higher tilt angles can be provided (+/- 90°).

An innovative option of the spectrometer is the multianalyser/ detector system. It allows a unique and flexible type of multiplexing. Using this option, a scattering angle range of 16° can be measured simultaneously, and flexible Q-ω paths can be realised without repositioning the instrument. Mapping of excitations is equally well possible as kinetic single-shot experiments on time scales that have not been accessible so far.

A unique feature of the instrument is the possibility to perform stroboscopic, time resolved measurements of both elastic and inelastic signals on time scales down to the microsecond regime. Using this technique, the sample is periodically perturbed by an external variable such as temperature, electric field, etc. The signal is then recorded not only as a function of momentum and energy transfer but also given a time stamp relative to the periodic perturbation.