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TOFTOF

Cold neutron time-of-flight spectrometer

TOFTOF scheme TOFTOF scheme

TOFTOF is a direct geometry multi-chopper time-of-flight spectrometer operated with incident neutrons from the undermoderated cold source of the reactor.
The 60 m long s-shaped curved primary neutron guide acts as a wavelength filter for the incident neutrons with a cutting edge at λi = 1.38 Å leading to a continuously high neutron flux over a wide wavelength range. Selecting an adequate incident wavelength and adjusting the chopper rotational frequency the resolution can be adapted to the needs of the experiment between 2 μeV and 3 meV. The scattered neutrons are detected by 1000 3He counting tubes mounted around the sample at distance of 4 m. The time-of-flight for each detected neutron is measured by the detector electronics with an accuracy up to 50 ns.
The prototype of a focusing neutron guide, parabolically shaped, has been recently installed, as alternative option to the final stage of the existing neutron guide. Its design combines the advantages of a supermirror coating with the leading-edge Adaptive Optics technology.

Typical Applications

TOFTOF represents a versatile instrument combining high energy resolution, high neutron flux (also at short wavelengths) and an excellent signal-to-background ratio. It is perfectly suited for both inelastic and quasielastic neutron scattering and a variety of scientific topics like:

  • molecular magnetism, quantum criticality in heavy fermion compounds, low energy excitations in multiferroic materials and novel magnetic phases (crystal field levels, phonons, magnons, polarons)
  • diffusion in liquid metals and alloys, simple liquids, colloids, disordered systems
  • aging effects in disordered media and low frequency dynamics in glasses
  • hydrogen storage materials
  • confined dynamics in nanostructures
  • energy-resolved QENS on proteins, vescicles and biological materials
  • biological activity and functionality of proteins and cells under pressure
Sample Environment

FRM II standard sample environment:

  • CCR / CryoFurnace (4 K – 600 K)
  • Circulation thermostat furnace (CTF 1)
  • (255 K – 450 K)
  • High temperature furnace (RT – 1800 °C)
  • CCR Cryostat (4 – 450 K)
  • 3He insertion device (down to 0.5 K)
  • circulation thermostat furnace (255 – 450 K)
  • high temperature furnace (25 – 1800 °C)

Sample environment provided by collaborators:

  • electromagnetic levitator
  • electrostatic levitator
  • hydraulic pressure cells (up to 3.5 kbar)
  • clamp pressure cells (few GPa)

Technical Data

Primary Beam

  • Neutron guide: NL2au
  • Number of chopper discs: 7
  • Chopper frequency range: 400 min-122000 min-1
  • Diameter of chopper disc: 600 mm
  • Cross section of neutron guide at the entrance: 44 × 100 mm2
  • Cross section of neutron guide
    20 cm in front of sample position: 23 × 47 mm2

Main Parameters

  • Adjustable range of incident neutrons: 1.4 – 16 Å
  • Elastic energy resolution: 2 µeV – 3 meV
  • Range of energy transfers: -30 meV – 50 meV
  • Integral neutron flux of the white beam at sample position: 1010 n cm-2 s-1
  • Angular range of the detector bank: -15° to -7° and 7° to 140°

Instrument Scientists

Dr. Giovanna Giulia Simeoni
Phone: +49.(0)89.289.14975
E-Mail:

Dr. Wiebke Lohstroh
Phone: +49.(0)89.289.14735
E-Mail:

TOFTOF
Phone: +49.(0)89.289.14881

Operated by

TUM

Gallery

Elastic resolution
Elastic resolution

Figure 1: Elastic resolution as a function of the incident neutron wavelength for selected chopper rotational frequencies.

Dynamic range of the TOFTOF spectrometer
Dynamic range of the TOFTOF spectrometer

Figure 2: Dynamic range of the TOFTOF spectrometer for different
incident wavelengths.

Neutron flux
Neutron flux

Figure 3: Incident differential white neutron flux at the sample position as measured by a calibrated beam monitor.

TOFTOF
TOFTOF

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