Direct magnetocaloric characterization and simulation of thermomagnetic cycles.

An experimental setup for the direct measurement of the magnetocaloric effect capable of simulating high frequency magnetothermal cycles on laboratory-scale samples is described. The study of the magnetocaloric properties of working materials under operative conditions is fundamental for the development of innovative devices. Frequency and time dependent characterization can provide essential information on intrinsic features such as magnetic field induced fatigue in materials undergoing first order magnetic phase transitions. A full characterization of the adiabatic temperature change performed for a sample of Gadolinium across its Curie transition shows the good agreement between our results and literature data and in-field differential scanning calorimetry.

Hexapod control for an active secondary mirror: general concept and test results.

Active control of the secondary mirror, mainly for correction of the decentering coma, is an essential tool for an active-optics telescope. The Italian Telescopio Nazionale Galileo is equipped with a secondary mirror supported by an hexapod mechanical structure, providing a positioning control with six degrees of freedom. The hexapod system has been built and tested to characterize its performance. The results show that the errors in the positioning of the secondary mirror lead to an aberration image well below the diffraction figure of the telescope.

Optical performances of the Ultraviolet Coronagraph Spectrometer of the Solar Heliospheric Observatory.

The optical performances of the spectrometer assembly for the Ultraviolet Coronagraph Spectrometer of the Solar and Heliospheric Observatory mission have been tested. The flight unit of the spectrometer assembly, consisting of the structure equipped with the entrance slits assembly, the grating drive mechanisms mounting two toroidal gratings, and the photon-counting detectors, has been integrated and aligned; also the flight unit of the White Light Channel has been integrated and aligned in the spectrometer assembly. Tests with both visible and UV radiation have been performed. Aberration and stray-light measurements have shown that the instrument performs satisfactorily, almost in compliance with the scientific requirements; also some measurements of the polarimeter modulation curve and the relative error have shown performances within the specified requirements.