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TASSE

The IN20/TASSE is a Spin Echo (SE) option to be mounted on the IN20 thermal polarised neutron three-axis spectrometer (TAS). The purpose of this instrument is to measure excitations with a μeV resolution.

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This page gathers information about the capabilities and the scope of the IN20/TASSE Spin Echo option.
In order to obtain beam time, contact E. Farhi <farhi(at)ill.fr>, M. Enderle <enderle(at)ill.fr> for proposal submissions

TASSE scope

The IN20/TASSE is a Spin Echo (SE) option to be mounted on the IN20 thermal polarised neutron three axis spectrometer (TAS). Essentially, the TAS spin-echo technique provides an accuracy equivalent to the Raman and Brillouin light scattering at zone center (q=0) or zone border, but for any q and energy value.


The purpose of TASSE is to measure excitations :

  • damping/life times/line width with μeV resolution
  • energy shifts with μeV resolution (for inelastic scattering).

As a complement, some additional usage may be envisaged :

  • depolarisation effects (magnetic samples)
  • phase shift effects and spin rotation at the sample
  • interference effects between close excitations to appear in the echo enveloppe, which enables in principle to measure small gaps.
The TASSE option installed on IN20
A closer view on one of the magnetic coils

Limitations of IN20/TASSE

Presently, the instrument is not designed for studies of very dispersive excitations even though gradient coils have been designed to perform a slope and curvature focusing of the echo (which usually tends to blur with dispersive excitations). These coils are unfortunately responsible for a high loss in intensity.
However, in standard configuration (without gradient coils), if the dispersion remains limited, the echo bluring appears as an effective instrumental damping which is to be substracted to the overall measured damping in order to extract the excitation damping. The phase shift is less affected by this effect, as long as the dispersion sheets do not change dramatically.