Journal of large-scale research facilities, 1, A13 (2015) http://dx.doi.org/10.17815/jlsrf-1-36 Published: 19.08.2015 PUMA: Thermal three axes spectrometer Heinz Maier-Leibnitz Zentrum Georg-August-Universität Göttingen Technische Universität München Instrument Scientists: - Oleg Sobolev, Institute of Physical Chemistry, Georg-August-Universität Göttingen at Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany, phone: +49(0) 89 289 14754, email: oleg.sobolev@frm2.tum.de - Jitae T. Park, Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, Germany, phone: +49(0) 89 289 13983, email: jitae.park@frm2.tum.de Abstract: Three axes spectrometers allow the direct measurement of the scattering function S(Q, ω ) in single crystals at well de�ned points of the reciprocal lattice vector Q and frequency ω and thus rep- resent the most general instrument type. PUMA, which is jointly operated by the Institute of Physical Chemistry, Georg-August-Universität Göttingen and the Technische Universität München, is charac- terised by a very high neutron �ux as a result of the e�cient use of focussing techniques. 1 Introduction Three di�erent vertical openings and a horizontal slit with a maximum opening of 40 mm de�ne the virtual source, which is two meters before the monochromator. To reduce the primary beam’s contam- ination by epithermal neutrons, a sapphire �lter can be placed in front of the monochromator. PUMA has a remote controlled monochromator changing unit which allows to place one out of four di�erent monochromators inside the drum. All of them are equipped with double focussing devices that allow for optimum focussing conditions over a wide range of incident wavevectors ki. The horizontal diver- gency of the beam can be de�ned using a series of four Soller collimators. The two inside the drum, before and after the monochromator, can be remotely changed, whereas the two in the analyzer hous- ing can be changed manually. An Eulerian cradle can optionally be used to access the four dimensional Q-ω -space. An innovative option of the spectrometer is the multianalyzer/ detector system. It allows a unique and �exible type of multiplexing. Using this option a scattering angle range of 16° can be measured simultaneously and �exible Q-ω paths can be realised without repositioning the instrument. Mapping 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-1-36 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 1, A13 (2015) http://dx.doi.org/10.17815/jlsrf-1-36 Figure 1: Instrument PUMA (Copyright by W. Schürmann, TUM). 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 measure- ments 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 �eld, 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. 2 Typical Applications • Phonons Electron-phonon interaction Phonon anharmocities Soft mode phase transitions • Magnons Spin waves in (anti)ferromagnets Electron-magnon interaction Unconventional superconductors Crystal �elds • Time resolved/ stroboscopic measurements Temperature cycling (excitations during demixing processes) Electrical �eld cycling (polarisation processes in ferroelectrics) Temperature/ pressure cycling • Di�raction; purely elastic signals Superstructures/ satellites Di�use scattering 2 http://dx.doi.org/10.17815/jlsrf-1-36 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-1-36 Journal of large-scale research facilities, 1, A13 (2015) Figure 2: Schematic drawing of PUMA. 3 Sample Environment Besides standard sample environment, we provide: • Closed-cycle cryostates 3.5 – 300 K; – 650 K with adaptable heating device • Cryofurnace 5 K – 750 K • Paris-Edinburgh type pressure cell p < 10 GPa Along with the detector electronics required for time resolved measurements, special sample environ- ment for the rapid cycling is available: • Furnace for fast temperature jumps (∼ 5 K/s cooling rate; < 620 K; ambient atmosphere) • Switchable HV power supply (< 500 Hz; +/− 10 KV) 4 Technical Data 4.1 Primary beam • Beam tube SR-7 (thermal) • Beam tube entrance: 140 x 90 mm2 • Virtual source dimensions: horizontal: 0 – 40 mm vertical: (90, 110, 130 mm) 4.2 Distances • Beam tube entrance – monochromator: 5.5 m • Virtual source – monochromator: 2.0 m • Monochromator – sample: 2.0 (± 0.1) m • Sample – analyzer: 1.0 (± 0.1) m • Analyzer – detector: 0.9 m 3 http://dx.doi.org/10.17815/jlsrf-1-36 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 1, A13 (2015) http://dx.doi.org/10.17815/jlsrf-1-36 4.3 Collimation • Remote controlled: α 1: 20’, 40’, 60’ α 2: 14’, 20’, 24’, 30’, 45’, 60’ • Manually changeable: α 3: 10’, 20’, 30’, 45’, 60’ α 4: 10’, 30’, 45’, 60’ 4.4 Monochromators • Crystals: PG(002), Cu(220), Cu(111), Ge(311), size: 260 x 162 mm2; • Focus vertically and horizontally adaptable to incident energy 4.5 Analyzer • Crystals : PG(002), Ge(311); 210 x 150 mm2 vertical �xed focus horizontally adaptable to incident energy 4.6 Sample table • Diameter 800 mm • Max. load 900 kg • Amagnetic goniometer (± 15°) • Z translation (± 20 mm) • Optional Eulerian cradle 4.7 Main parameters • Monochromator take-o� angle: -15° < 2Θ < -115° • Scattering angle sample: -70° < 2Θ < 120° (dependent on monochromator take-o� angle) • Analyzer scattering angle: -120° < 2Θ < 120° • Incident energy range: 5 meV – 160 meV • Momentum transfer range: < 12 Å-1 • Energy transfer: < 100 meV 4 http://dx.doi.org/10.17815/jlsrf-1-36 https://creativecommons.org/licenses/by/4.0/ Introduction Typical Applications Sample Environment Technical Data Primary beam Distances Collimation Monochromators Analyzer Sample table Main parameters