An automatic ultrasonic welding process for interconnecting superconducting wires of the CERN Large Hadron Collider (LHC)

The Large Hadron Collider (LHC), the next research tool for particle physics at CERN, is due to start operation in 2005. The main components of the LHC are the superconducting twin-aperture magnets, operating at a temperature of 1.9 K. A large number of auxiliary superconducting wires have to be interconnected in series to electrically feed, at 600 A, the main dipole and quadrupole corrector magnets. To interconnect these wires, an ultrasonic welding process has been developed and compared to the former soft-soldering technique. An industrial ultrasonic welding machine has been adapted and automated to satisfy the reliability and reproducibility. A high strength mechanical junction between wires has been obtained over the operating range from 293 K to 1.9 K. Results of mechanical and electrical validation tests are presented

Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography

The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was established by simulatio

EPR INVESTIGATIONS OF SIZE EFFECTS IN THE CRYSTAL FIELD OF SMALL DIELECTRIC PARTICLES OF Gd3+-DOPED SrCl2

Des petits amas (~ 100 Å de diamètre) de SrCl2 dopé avec des ions Gd3+ ont été préparés par évaporation d'un échantillon massif dans une faible atmosphère d'argon. Des mesures de résonance paramagnétique électronique (RPE) ont été effectuées en bande X et à température ambiante. Les petits amas présentent un spectre différent de celui observé dans le cas d'un échantillon massif sous forme de poudre. Premièrement, une augmentation du paramètre de champ cristallin cubique |b4| de 1,6 ± 0,l % a été observée et interprétée comme étant due à une contraction de la maille du réseau d'environ 0,27 %. Deuxièmement, les raies correspondant aux transitions RPE sont considérablement élargies dans le cas des petits amas. Un recuit à 400 °C pendant 1 min. provoque la coalescence des amas et après recuit, le paramètre b4 et les largeurs de raie sont identiques à ceux mesurés dans l'échantillon massif.Small particles (~ 100 Å in diameter) of Gd3+-doped SrCl2 have been prepared by evaporating a bulk sample in a low-pressure argon atmosphere. EPR measurements were made at X-band and room temperature. In the case of small particles, the observed Gd3+ spectrum exhibits two significant differences relative to the bulk powder spectrum. First, the cubic crystal-field parameter |b4| is increased by 1.6 ± 0.1 % for the small-particle sample. This effect is interpreted as due to a lattice-parameter contraction of approximately 0.27 % as compared to the bulk material. Second, the line widths of the EPR transitions are consistently larger in the small-particle case. Annealing at 400 °C for 1 min. coagulates the small particles and, following this anneal, the parameter b4 and the line widths are equal to those of the bulk material