Many investigations in quantum magnetism and in physics of highly correlated electrons deal with spin-1/2 systems; whose correlations are often short-ranged and short-lived. Their signals in the Q,ω space are, hence, intrinsically weak, broadened both in energy and in momentum transfer, making them much more  difficult to be distinguished from background as compared to classical collective excitations such as spin-waves or phonons. The energy scale of the magnetic Hamiltonians is often on the 0.1 to 10 meV scale. This implies on one hand the need to access low temperatures, often down into the 10 mK range, to explore the related ordering processes. On the other hand the relatively low energy scale opens the possibility to influence directly the spin Hamiltonian and to tune the magnetic dynamics by external parameters like pressure or magnetic field of the order of 10 to 15 T. Complex sample environment equipment such as high-field magnets, dilution fridges or pressure cells, and their combinations, are therefore indispensable for successful experiments. Although optimized for neutron spectroscopy, this equipment nevertheless attenuate neutron beams by absorption in the wall materials and impose geometrical constraints both on the sample size and on the beam geometry. The neutron losses can often be compensated by trading angular (momentum) resolution for neutron flux, while keeping a good energy resolution. In practice this means that it is imperative for ThALES to provide a flexible beam definition system offering the possibility to focus the neutron beam onto a small sample volume and to minimize the sources of parasitic scattering (background).

Thales will extend the incident neutron spectrum towards higher energies - E_i^max ≈ 25 meV as compared to the 12 meV at present on IN14. The largely extended kinematic range will provide an ample overlap with the energy and momentum transfers accessible on the thermal neutron TAS (IN8, IN20, IN22).

The demand in beam time for cold neutron polarized spectroscopy on IN14 increases steadily - from 10% in 2006 to 30% in the first half of 2009 - but is still limited by neutron count-rate losses of about an order of magnitude related to the lower efficiency of devices used to produce polarized neutron beams and to analyze the polarization of the scattered beam. ThALES will provide an important step forward by employing a state of the art doubly focusing polarizing monochromator and analyzer (Heusler alloy, analogous to those successfully used on IN20). Moreover there will be a possibility to employ the newly developed wide-angle polarized ³He-filter in connection with the FlatCone multianalyzer option. In both cases the luminosity of the polarization analysis set-up of ThALES should be comparable to that of the present unpolarized IN14 and, hence, make the polarization analysis technique accessible to a wide class of experiments.