The challenging optics ofXtremeD– a neutron diffractometer for high pressures and magnetic fields at ILL developed by Spain

Abstract

Abstract. The Spanish community of neutron scatterers and the ILL are considering the construction of a CRG "eXtreme conditions Diffractometer (XtremeD)" for both single crystals and powders, operating at high pressures (up to 50 GPa) and high magnetic fields (up to 15 Tesla). High pressure studies require reduced sample volumes. This makes the focusing optics a crucial part of the instrument, in order to have increased flux and to avoid the scattering from the sample environment. The different solutions at different levels of the instrument, which are being studied, will be discussed in this paper. IntroductionOver the last few years, there has been a regain in the interest on scientific problems related to the behaviour of matter under extreme conditions of pressure, magnetic field and temperature [1]. Neutron diffraction has unique capabilities for this kind of research and the interest for this technique, in particular in the Spanish scientific community, has led to the proposal for the construction at ILL of a new neutron diffractometer optimized for high pressure and high magnetic field studies for both single crystals and powders, which will be developed by Spain. At the present time we are finalizing the technical project, and the construction phase is expected to start in 2011.There are fundamental differences between synchrotron X-ray beams, which are intrinsically small and well collimated, and neutron sources, which are both large in size and have a large divergence [2]. The neutron phase space is approximately 1000 times less dense than X-ray phase space. On the other hand, the lower fluxes of neutrons and the lower interaction of neutrons with matter compared with Xrays makes necessary the use of much bigger samples than in synchrotron X-ray experimentation. For these reasons, the experimentation with very high pressures is a challenging field for neutrons. The small sample size -around 1mm 3 -required in order to reach pressures above 10GPa implies that the focalization of the beam is absolutely necessary in order to have increased flux to compensate for the small sample and to avoid the spurious scattering from the sample environment. Different solutions at different levels of the instrument are being studied and will be discussed in this contribution, such as a focusing guide, different types of focusing monochromators, collimators, or the possibility of