| Popis: |
The research work described in this thesis has been dedicated to the subject of the magnetic diagnostic for ITER and neutron & y-ray detection for the RFX experiment. The main topic has been focused on the design of a novel concept of magnetic pick-up coil, based on the Low- Temperature Co-fired Ceramic (LTCC) technology, which had been proposed during the conceptual design phase for the ITER in-vessel magnetic diagnostic system. The design has been developed up to the preliminary design level in the framework of an international collaboration, led by Consorzio RFX and supported by the European Agency Fusion for Energy (F4E) and by ITER Organization (ITER-O). The activities carried out during the doctoral period concerned several aspects of plasma diagnostic design: from thermo-mecanical to neutronic numerical analyses; from vacuum technology studies to the setting-up and execution of thermo-electrical tests on sensor prototypes. In the final part of the doctoral period the competence gained has been applied to the setting-up and the exploitation of a neutron and photon detection system for RFX-mod. The major results obtained in the various thematic areas are described in the following chapters: Theoretical framework and background (Chapters 1, 2 and 3): In these chapters, after a basic introduction about fusion science, the theoretical bases and the main arguments that motivated this study are described, with specific emphasis on magnetic diagnostics. This phase is supported by an extensive literature review and a summary of results from previous R&D activities on pick-up coils based on Low Temperature Co-fired Ceramic (LTCC) technology, which lead to the design of a new set of prototypes improved in order to achieve the ITER requirements. LTCC sensor prototypes characterization (Chapter 4): This chapter describes a series of tests to characterize the magnetic sensor prototypes, developed in order to finalize the detailed design of sensors for ITER magnetic diagnostic. For this purpose a formal test protocol for a full characterization of the sensors is reported. In particular these tests have been focused on dimensional and planarity analysis, electrical, magnetic and thermo-electrical characterization, executed on a new set of 40 LTCC sensor prototypes (third generation). Vacuum compatibility (Chapter 5): This chapter describes the main issues related to the vacuum compatibility of the in-vessel components, such as magnetic sensors. The design proposal of a test rig for outgassing rate measurements has been developed. A detailed description of the system, cost estimation and CAD assembly design is reported. Mechanical sensor assembly (Chapter 6): This chapter describes the thermo-mechanical aspects related to the support structure designed to attach the sensors inside the vacuum vessel. Several topics have been investigated with proper thermo-mechanical fem analyses and experimental tests, such as: assessment of temperature gradients within sensor assembly, to minimize possible measurement noise due to thermoelectric sensitivity; mechanical optimization of stress and deformation induced by welding; technical feasibility study for a suitable method of welding for LTCC electrical connections. Simulations of LTCC sensors under n irradiation (Chapter 7): This chapter is focused on the estimation of the nuclear heat [W/cm^3 ] induced by neutron reactions within LTCC sensors, considering a set of expected neutron flux spectra [n/cm^2/s] under the Blanket modules of ITER. For this propouse a set of Monte Carlo neutron interaction simulations have been carried out using a detailed model of the sensor and two potential locations for installation. RFX-mod as n and gamma source (Chapter 8): This chapter summarises the activities of installation of two scintillator detectors (Nal Scintillator and NE213 Liquid Scintillator) executed during the experimental campaign (January-September 2014) at RFX experiment, as part of the first experimental measurements of neutron and photon production in RFX-mod deuterium plasmas. A total of 1185 shots have been monitored over 7 months of experimental campaign, background particle detection and magnetic shielding, as well as data acquisition and calibration issues are reported |
