B. Jenninger

Industrial surfaces behaviour related to the adsorption and desorption of hydrogen at cryogenic temperature

The determination of the hydrogen adsorption capacity on different industrial surfaces has been carried out by measuring isothermal adsorption. First results show that the adsorption capacity is mainly determined by surface porosity. Therefore, the samples may be classified into two categories: smooth and porous surfaces. Thermal desorption spectra reveal two adsorption energy levels for hydrogen physisorbed on porous materials, but only a single one on smooth samples. The value of the lowest energy level seems to be independent of the substrate nature. The physisorption process studied at low coverage, well below a monolayer, shows that these two levels are not well defined but an energy distribution exists for each of them. The influences of the isotherm temperature and an annealing at 7 K of an adsorbed monolayer on hydrogen adsorption capacity have been studied.

Performances of various types of benders for sagittally focusing crystals on ESRF synchrotron beamlines

Different types of crystal bending devices have been developed at the ESRF in the past few years for sagittal focusing of relatively wide bending magnet and wiggler synchrotron x-ray beams and of more tightly collimated undulator radiation. Their basic features and performances are presented, together with practical experience. A new bender for dynamical microfocusing of undulator beams down to micrometer spatial resolution with high efficiency is described.

Characterisation of net type thermal insulators at 1.8 K low boundary temperature

The Large Hadron Colliders superconducting magnets are cooled by superfluid helium at 1.8 K and housed in cryostats that minimise the heat inleak to this temperature level by extracting heat at 70 K and 5 K. In the first generation of prototype cryostats, the radiative heat to the 1.8 K temperature level accounted for 70% of the total heat inleak. An alternative to enhance the cryostat thermal performance incorporates a thermalised radiation screen at 5 K. In order to avoid contact between the 5 K radiation screen and the cold mass, insulators are placed between both surfaces. Sets of commercial fibre glass nets (spacers) are insulator candidates to minimise the heat inleak caused by any accidental contact between the two temperature levels. A model to estimate their performance is presented. A set-up to thermally characterise them has been designed and is also described in the paper. Finally, results as a function of the number of nets forming the spacer, the boundary temperatures and the compressive force in the spacer are presented.