CRYSTAL ORIENTATION EFFECTS DURING FABRICATION OF SINGLE OR MULTI-CRYSTAL NB SRF CAVITIES*

Abstract Single and large-grain Nb SRF cavities are of interest due to possible reduction of cost and problems associated with inconsistent texture and surface finish among batches of rolled polycrystalline Nb sheet. The effect of crystal orientation on dislocation density, surface quality, and recrystallization after plastic deformation and e-beam welding was investigated, as understanding of their interrelations is needed. These were evaluated for three samples of different orientations at steps similar to those in typical cavity forming, with deformation modeled using a crystal plasticity approach. Initial dislocation density was higher than expected, increased with deformation, after welding was reduced in recovered areas, and was similar to initial density in recrystallized grains; there was also evidence that Nb has a higher tolerance for dislocations than other metals. Surface quality depends on a complex relation of crystal orientation, slip system activity, and prior surface treatment. Recrystallization nucleated outside the melt pool, and the new orientations grew both epitaxially into the weld as it solidified, and away until heat and time were insufficient to continue growth

Neutrino interactions at few MeV: results from Borexino at Gran Sasso

Borexino, at the I.N.F.N. Gran Sasso Underground Laboratory in Italy, is an experiment designed to detect, in real-time, low energy solar neutrinos. After a brief presentation of the Borexino physics and detector, we illustrate some recent results and their physics implications. Borexino perspectives are also discussed