Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich
Logo

MLZ (eng)

Lichtenbergstr.1
85748 Garching

PUMA

Thermal three axes spectrometer

PUMA Scheme PUMA Scheme

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 characterized 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 meters before the monochromator. To reduce the contamination of the primary beam by epithermal neutrons, a sapphire filter can be placed in front of the monochromator. PUMA has a remote controlled monochromator changing unit, which allows to place one out of four different monochromators inside the drum. At present two different monochromators (PG (002) and Cu (220)) are available, covering an energy transfer up to 100 meV — Cu(111) and Ge(311) are in preparation. All monochromators are equipped with doubly focussing devices that allow for optimum focussing conditions over a wide range of incident wavevectors ki. The horizontal divergency of the beam can be defined using a series of four Soller collimators. The two inside the monochromator drum, before and after the monochromator, can be remotely changed, whereas the two in the analyzer housing can be changed manually.
An Eularian 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 flexible type of multiplexing. Using this option a scattering angle range of 16° can be measured simultaneously and flexible Q-ω paths can be realized without the need to reposition 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.

Typical Applications

Phonons

  • Electron / phonon interaction
  • Phonon anharmocities
  • Soft mode phase transitions

Magnons

  • Spin waves in antiferromagnets
  • Kinematic / dynamic interaction
  • Electron-magnon interaction
  • Unconventional superconductors
  • Crystal fields

Time resolved / stroboscopic measurements

  • Temperature cycling (excitations during demixing processes)
  • Electrical field cycling (polarization processes in ferroelectrics)
  • Temperature / pressure cycling

Diffraction; purely elastic signals

  • Superstructures / satellites
  • Diffuse scattering

Sample Environment

Aside from the FRM II standard sample environment the following dedicated devices are provided:
Closed-cycle cryostates 3.5 – 300 K;

  • -650 K with adaptable heating device
  • Cryofurnace 5 K – 750 K
  • Paris-Edinbourgh type pressure cell p < 10 GPa

Along with the detector electronics required for time resolved measurements, special sample environment for the rapid cycling is available:

  • Furnace for fast temperature jumps (~ 5 K/s cooling rate; < 620 K; ambient atmosphere)
  • Mirror furnace (~ 5 K/s; < 1270 K; vacuum/ inert gas (Ar/ N2) atmosphere); under development
  • Switchable HV power supply (< 500 Hz; +/- 10 KV)

Technical Data

Primary beam:

  • Beam tube SR 7 (thermal)
  • Beam tube entrance: 140 × 90 mm2
  • Virtual source dimensions:
    • horizontal: 0 – 40 mm
    • vertical: (90, 110, 130 mm)

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

Collimation:

  • Remote controlled:
    • α1: 20’, 40’, 60’
    • α2: 14’, 20’, 24’, 30’, 45’, 60’
  • Manually changeable:
    • α3: 10’, 20’, 30’, 45’, 60’
    • α4: 10’, 30’, 45’, 60’

Monochromators:

  • Crystals: PG(002), Cu(220), Cu(111); size: 260 × 162 mm2
  • Focus vertically and horizontally adaptable to incident energy

Analyzer:

PG(002), Ge(311); 210 × 150 mm²; vertical fixed focus; horizontally adaptable to incident energy

Sample table:

  • Diameter 800 mm
  • Max. load 900 kg
  • Amagnetic goniometer (± 15°)
  • Z translation (± 20 mm)
  • Optional Eularian cradle

Main parameters:

  • Monochromator take off angle:
    -15° < 2Θ < -115°
  • Scattering angle sample:
    -70° < 2Θ < 120°
    (dependent on monochromator take off angle)
  • Analyzer scattering angle:
    -120° < 2Θ < 120°
  • Incident energy range: 5 meV – 160 meV
  • Momentum transfer range: < 12 Å-1
  • Energy transfer: < 100 meV

Instrument Scientists

Dr. Jitae Park
Phone: +49.(0)89.289.13983
E-Mail:

Dr. Oleg Sobolev
Phone: +49.(0)89.289.14754
E-Mail:

Dr. Anke Teichert
Phone: +49.(0)89.289.14756
E-Mail:

PUMA
Phone: +49.(0)89.289.14914

Cooperation team

Götz Eckold (Project leader)
Georg August University Göttingen
Institute for Physical Chemistry (IPC)
Phone: +49.(0)551.39.33143
E-mail:

Volker Meyer and staff (Mechanics workshop IPC Göttingen)
Georg August University Göttingen
Institute for Physical Chemistry (IPC)
Phone: +49.(0)551.39.33157
E-mail:

Andreas Knorr and staff (Electronics workshop IPC Göttingen)
Georg August University Göttingen
Institute for Physical Chemistry (IPC)
Phone: +49.(0)551.39.33159
E-mail:

Operated by

Uni Göttingen
TUM

Gallery

PUMA
PUMA

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich