No abstract available

[en] Magnetic tunnel junctions based on MgO(0 0 1) barriers and ferromagnetic electrodes, such as Fe/MgO/Fe, represent a very popular and widely investigated subject in the field of spin-electronics because of the large values of magnetoresistance shown by these systems. In this paper, the structural properties of MgO thin films grown onto Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O surfaces, with MgO thickness ranging from 2 to 14 equivalent monolayers, have been investigated by means of Auger electron diffraction. The structural order and the crystal quality of the MgO films result practically independent from the template, the latter being either the clean Fe(0 0 1) surface or the oxidized Fe(0 0 1)–p(1 × 1)O one. This is confirmed by numerical simulations, showing that, apart from the first two MgO layers close to the interface, the structure is unaffected by the choice of the starting surface. By a structural point of view, we can conclude that Fe(0 0 1)–p(1 × 1)O is a good candidate for the role of bottom electrode for the realization of MgO-based magnetic tunnelling junctions, also considering its higher chemical stability and reproducibility if compared to the clean Fe(0 0 1) surface.

[en] A superconducting wiggler magnet has been successfully tested at ANSALDO COMPONENTI works. The design field of 6 Tesla has been reached after limited training. The field of 6.025 ± 0.003 Tesla has been measured by means of a flip coil connected to an integrating magnetometer. Field profile measurements were made at 5.0, 5.75 and 6.025 Tesla, during which time, the magnet showed high stability. The overall cryogenic losses have been measured and they are consistent with the computed ones

[en] Conversion of an electron beam to a positron beam is obtained at the end of the first four accelerating guides of the Frascati linac, using an electron current of 200 mA peak, at 85 MeV, having a pulse width of 4 μs and a repetition rate variable between 3 and 250 pps. Two different fixed targets have been designed: a high average power target used to produce a high duty cycle (4μs, 250 pps) positron beam for nuclear physics experiments, and a high positron production efficiency, low average power target, used for injection of positrons into the storage ring, Adone, when a beam repetition rate of only 3 pps is allowed, but a high positron yield is required, to reduce the ring filling time. (Auth.)

[en] In this paper we present some design considerations for the LELA (Laser a Elettroni Liberi su Adone) undulator magnet (lambdasub(q) = 11.6 cm, K = 3.6, N = 20) now in construction. We also report the measurement performed on a two periods full scale prototype magnet built in the LNF. (orig.)

[en] Activities on RF superconductivity at INFN laboratories in Frascati, Genova, Milano are mainly oriented towards the realization of high gradient cavities and construction of test accelerators for high energy physics. The activities consist in the construction of a test 50 MeV accelerator (LISA) and in the development of SC RF cavity prototypes and low emittance RF guns. The interest is both in bulk Nb and in films sputtered on copper. Characterization of films of various materials is carried on. The construction of a 25 to 50 MeV linear SC accelerator (LISA) is in progress. The aims of the project are to study the problems of SC linacs with high quality, high peak current beams. Facilities have been set up for testing complete SC resonator cells with RF power. They consist of a vertical cryostat 2.7 meter deep, a 1 kW 500 MHz amplifier, electronic instrumentation and a data acquisition system for the temperature mapping. Moreover, basic handling tools such as a laminar flow panel wall arranged in a dedicated room, and an ultra-pure water system are now available. Studies on sputtered thin films are briefly outlined. (N.K.)

[en] To improve the performance of the Adone colliding beams the conventional transverse wiggler magnet is designed. The wiggler maqnet will be installed in one of the four available 2.5 m long interaction straights of Adone. The design aims are: 5 full poles, 2 half-poles; field at the centre of gap - 18 kOe. Effects of the wiggler on damping, momentum spread and beam emittances are calculated. It is shown that wigglers modify the beam emittance. The use of two wigglers is envisaged for two-beam operation. The expected behaviour of luminosity and current per bunch as a function of energy are shown

No abstract available

[en] In the DAΦNE Φ Factory, electrons and positrons circulate in two separate storage rings, whose top view is about elliptical, intersecting in the horizontal plane, giving rise to two interaction points. A hybrid, tunable, p.m. quadrupole prototype, 5.3 T/m, 45 mm bore radius, 280 mm in length, for DAΦNE has been designed and built. Magnetic calculation, constructive design and the first acceptance test results are briefly reported. The magnetic measurement program is not yet completed and a deeper investigation is still needed. (R.P) 5 refs.; 5 figs

[en] Full text: Since the discovery of superconductivity in alkali-doped solid C₆₀, the electronic structure of the host material (C₆₀) and the doped compounds (A_xC₆₀, where A is an alkali metal), has been the subject of a considerable amount of work, both theoretical and experimental. The spectroscopic investigations of the alkali-doped C₆₀ compounds has been mainly focussed on the valence states, while much less information is available on the unoccupied states. In particular, inverse photoemission data on the complete set of stable Rb_xC₆₀ compounds was, so far, still missing. We have performed Inverse Photoemission (IPE) spectroscopy on Rb_xC₆₀ compounds (x = 1, 3, 4, 6). IPE spectra were obtained using a band-pass photon detector (hv = 9.4 eV, FWHM = 0.7 eV) and scanning the kinetic energy of the electrons impinging on the sample. Rb was evaporated on C₆₀ films (thickness = 6-12 atomic layers) grown in situ on a Cu(100) substrate. The temperature of the substrate was kept equal to T = 100 deg C, which is lower than the C₆₀ sublimation temperature. The amount of Rb was checked by measuring the intensity of the C1s and Rb3d photoemission lines. After the required amount of Rb had been deposited, the samples were annealed to distillate the desired stable phase