Mario, Isabella (2016) IR thermography analysis of the powerful hydrogen beam at ELISE. [Magistrali biennali]
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Thermonuclear fusion will supply the world with a safe, environmentally friendly energy source. Neutral beam injectors (NBI) provide a heating system and a current drive system for thermonuclear plants. The deuterium-tritium mixture that consists in the fuel of such thermonuclear reactors is in a plasma state and it is magnetically confined in a toroidal-shaped vessel. In ITER, the international thermonuclear experimental reactor, under realisation in Cadarache (FR), two NBI of 16.5 MW each will be installed. The ITER-like neutral beam injector described in section 1.3 is based on H-/D- RF source whose design was developed at the Max-Planck Institut fur Plasmaphysik (IPP). The use of negative ions is mandatory to reach high neutralisation efficiencies in case of beams of 1MeV energy (ITER requirements). In the source a plasma is ignited by means of RF coils, then the beam is formed and accelerated by a grid system. The extraction and acceleration stages consist in potential steps applied to grids disposed perpendicularly to the beam-line. At the IPP are present a 1/8 ITER-size prototypes and the test facility ELISE (1/2 ITER-size source) that aims to investigate the physics behind the ion sources with an extraction area is about 1000 cm2. ELISE, whose design and beam diagnostics are described in chapter 2, is an important step between small-scale prototypes and the full size ITER source. This thesis aims to characterize the beam properties of ELISE, in particular the beam width and the beam deflection, in different operational conditions by means of the IR analysis of the beam profile on a diagnostic calorimeter. The analysis described in 3.2 is automatized and the beam parameters measured from the beam imprint on the calorimeter are automatically collected in a database. The emissivity calibration was performed using the temperature measured by thermocouples embedded on the calorimeter. In section 3.3 a initial cross-check with other beam diagnostics is performed in order to test the reliability and the robustness of the analysis. The beam parameters retrieved from the IR analysis are investigated as a function of operational parameters in chapter 4. The effects of the beam optics, acceleration potential and the pressure on the beam are studied in sections 4.1, 4.2 and 4.3. The plasma in the source is modified by means of applied electric and magnetic fields and by external magnets installed inside the source. The IR evaluation results as a function of operational parameters corresponding to the electric and magnetic field are discussed in sections 4.5, 4.6 and 4.4. The beam emission spectroscopy (BES) is a beam diagnostics that provides the beam divergence by means of the analysis of the Hα Doppler peak. The beam width retrieved by the beam imprint on the calorimeter and the beam divergence measured by the BES are compared. The spectra of BES indicate the presence of an additional broad component in the beam divergence that is investigated by means of the external portions of the diagnostic calorimeter. The cross-checks and analyses are described in section 4.7.
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