Zanini, Marco (2016) First extraction and acceleration operations of negative ion beams produced in NIO1 experiment. [Magistrali biennali]
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The research and the development of a Neutral Beam Injector as an auxiliary heating system is fundamental for ITER, the experimental reactor under construction in Cadarache (France) as a worldwide collaboration. This thesis work was performed on NIO1 experiment, developed at Consorzio RFX in collaboration with INFN-LNL. It consists in a radiofrequency negative ion source, with a maximum extracted current of 130 mA in H- ions, accelerated up to 60 kV by a three-grids system and it constitutes the testbed for the source of ITER neutral beam injector. In this work, the first NIO1 operation with beam extraction is described and analysed, in order to provide a beam characterization, using expecially electrical measurements. In chapter 1 a brief introduction about fusion physics and ITER is presented, with more emphasis regarding the external heating systems, while in chapter 2 an overview of NIO1 experiment is proposed. The following chapters review the effect of radiofrequency power and gas pressure on total extracted current. The analysis treats separately the current of negative ions and of electrons, extracted from the beam source together with the ions. Operations with oxygen as a filling gas are reported in chapter 3, while hydrogen operations are described in chapter 4. At the end of this chapter a comparison between the two gasses will be performed. In chapter 5 two ways are used to estimate the electron density: the first is based on a spectroscopical analysis of oxygen-argon emission lines. An alternative method, based on the Langmuir probe physics was developed and a comparison with spectroscopy measurements was performed. In chapter 6 conclusions are reported.
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