1,721,200 research outputs found
Optimization and control of the field quality, the mechanical structure and the quench protection of superconducting dipoles for future accelerators
No full textFuture particle accelerators will require future magnets, this work addresses most of the problems involved in designing and building state-of-the-art superconducting magnets for particle accelerators. These issues are field quality control, mechanical design, and quench protection. This thesis includes, for each of these three topics, a general introduction, a case study, and the specific solutions implemented for it. In particular, in the case of field quality and quench protection analysis the case study is the MBRD separation/recombination dipole (Main Bending Recombination Dipole, or D2 for short) for the high luminosity upgrade of the LHC, while for the optimization of the mechanical design it is the FalconD magnet (Future Accelerator post-LHC Cos-theta Optimized Nb3Sn Dipole), which is a prototype that represents an intermediate step between the high-field magnets obtainable with today's technology and the magnets that will be required for the Future Circular Collider (FCC), a 100 TeV hadron accelerator. As regards the analysis of the quality of the field, it was possible to define the stability of the magnetic design of D2 the magnet by evaluating the sensitivity of the harmonic content of the field generated as the tolerances of the components involved in the coils varied. In addition, the optimal shimming strategy needed to finalize production of the D2 prototype and another one to meet the field quality acceptance criteria for the series magnets was found. For what concerns the studies on quench protection, one of the most recent computational tools specialized in the simulation of quench phenomena (LEDET) was used, calibrated, and validated both by using another older software (ROXIE) and by the measurements carried out on the short model of the D2 magnet. Thanks to this simulation campaign it was possible to set up the tests that will be performed on the D2 prototype and to update the quench protection strategy, since these simulations demonstrated that the previous one did not comply with the safety limits imposed on the project. The forthcoming measurements on the D2 prototype will validate both the quality of the construction process, the simulation models used and the design choices that have been made. Finally, the mechanical optimization work (performed with the f.e.m. software ANSYS) consists of the design of both the 2D and 3D mechanical structure of the Falcon Dipole, which is both a high field magnet (12 T of bore field) and a brittle superconductor (Nb3Sn). For these reasons, the success of the project strongly depends on the optimal management of the high Lorentz forces generated in the coils
Microwave clocks and fountains
No full textIn this lecture a brief presentation of the physical principle of operation of microwave clocks is given. The three most important commercial microwave clocks (Cs beam, Rb cell, and H-maser) are briefly described, and the accuracy evaluation of a Cs fountain primary frequency standard is presented
Coherent microwave emission in cesium under coherent population trapping
No full textMicrowave emission has been observed at the ground-state hyperfine transition frequency of a cesium atomic vapor driven into a nonabsorbing state by means of coherent population trapping. The coherent emission observed is due to the oscillating magnetization generated by the coherence, which is induced between the ground-state hyperfine levels when they are coupled to an excited state by means of two laser radiations via a Λ scheme. The experiments described were done in a quartz cell containing buffer gases such as neon and nitrogen, reducing the linewidth through the Dicke effect. The cell was placed inside a microwave cavity tuned at 9.2 GHz, the ground-state hyperfine frequency of cesium, and a power output of the order of 100 fW was measured in the case where nitrogen was used as the buffer gas
Pulsed optically pumped frequency standard
No full textWe reconsider the idea of a pulsed optically pumped frequency standard conceived in the early 1960s to eliminate the light-shift effect. The development of semiconductor lasers and of pulsed electronic techniques for atomic fountains and new theoretical findings allow an implementation of this idea which may lead to a frequency standard whose frequency stability is limited only by the thermal noise in the short term and by the temperature drift in the long term. We shall also show both theoretically and experimentally the possibility of doubling the atomic quality factor with respect to the classical Ramsey technique approach
Slow light and superluminality in the coherent population trapping maser Aldo Godone, Filippo Levi, and Salvatore Micalizio
No full textThe propagation of a band-limited light pulse through an atomic medium under a Λ excitation scheme is theoretically analyzed in this paper. We consider in particular the case where the light pulse is detected through the coherent microwave emission of the atomic ensemble (coherent population trapping maser). Significant differences are predicted with respect to the more usual optical detection (electromagnetically induced transparency signal) and found in agreement with the experimental results. Higher signal delays were observed in the microwave emission than in the optical signal with an equivalent group velocity of 6 m/s as well as highly superluminal propagation under a proper modulation scheme. The experiments were performed with a thermal 87Rb vapor in buffer gas
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