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• W2908219098 abstract "The International Thermonuclear Experimental reactor (ITER), the world’s largest experimental facility in the realm of nuclear fusion for energy production, requires two Neutral Beam Injectors (NBI) rated for the total power of 33 MW for plasma heating and current drive. The ITER NBI includes an ion source which can produce 40 A of D¯ ions beams for 3600 s, accelerated at the energy of 1 MeV. The requirements for the ITER NBI are quite demanding and have never been achieved before all together in a single device. This specifically called for a development of the ITER Neutral Beam Test Facility (NBTF) called PRIMA (Padova Research on ITER Megavolt Accelerator) to carry out an international R&D program for the achievement of the ITER NBI requirements and the optimization of the operation in advance of the future use in ITER. The facility will host two experiments, SPIDER (Source for the Production of Ions of Deuterium Extracted from RF plasma), the full-size prototype of ITER RF ion source, and MITICA (Megavolt ITER Injector and Concept Advancement), the full-scale prototype of the ITER heating NBI. The NBTF in Padova, Italy, is ready, MITICA is currently under construction and SPIDER has been in operation since beginning of June 2018. The NBI ion source was initially based on filament type arc source, while for ITER the inductively coupled (IC) radio frequency (RF) ion source have been finally chosen in 2007. This is because RF sources present several advantages with respect to arc solutions; they have fewer parts and require less maintenance. In these ion sources, radio frequency plasma is generated at the frequency of 1 MHz and is characterized by high RF power density and low operational pressure (around 0.3 Pa).In the last decades, IC ion sources have been developed, studied and experimented at the Max-Planck-Institut fur Plasmaphysik (IPP) in Garching, Germany. The most recent one is ELISE (Extraction from a Large Ion Source Experiment), which is able to operate with both Hydrogen and Deuterium gas species and has half the size of ITER NBI source.Other accompanying activities have been recently launched at Consorzio RFX, Padova, Italy within the ITER NBI work program; one of them is a relatively small ion source called NIO1 (Negative Ion Optimization 1) working at 2 MHz, developed in order to gain experience on ion source operation and to study specific physics and engineering topics on a more flexible and accessible device than the SPIDER and MITICA. In addition, a small experimental test facility called HVRFTF (High Voltage Radio Frequency Test Facility) based on a high voltage resonance circuit that feeds a couple of electrodes in vacuum has been started at Consorzio RFX in 2014 to address and study the voltage holding capability of the RF components in the ion source at 1 MHz. The research endeavor during the three years of my PhD was carried out in the frame of the RF R&D task of the NBTF work-program at Consorzio RFX and during the mobility periods at the IPP.I have had the opportunity to work on two main lines: the first was dedicated towards the study of the RF power transfer efficiency of IC RF ion sources and the development of suitable models that will permit to explore possible improvements (in the future). In fact, the higher the efficiency, the lower can be the feeding power to the ion source and this may lead to a lower requirement both for cooling and for electrical insulation of the RF circuit components installed on the source. I have studied and analyzed several plasma heating mechanisms (like ohmic and stochastic heating in particular) and I have developed an electrical model which is responsible for describing the power transfer to the plasma. The first approach was based on a transformer model, and then a multi current filament model has been developed. This model is capable to account for the currents in the passive metallic structure within the driver region of the ion source and with this; it is able to overcome the main limitation of the transformer model. Furthermore, I have integrated all the models to develop a novel methodology to evaluate the efficiency of the RF power transfer to the hydrogen plasma in a cylindrical source. Then, I have implemented the methodology in a MATLAB® code and applied it to the driver of ELISE and NIO1 ion sources showing the results in terms of plasma equivalent resistance and power transfer efficiency obtained as a function of applied frequency and plasma parameters (electron density and gas pressure).The second part of my work was directed towards the design, construction and set-up of the HVRFTF. I gave an important contribution in terms of the electrical characterization of the RF resonance circuit components (mainly the two solenoid coupled inductor), thermal analysis of the electrodes placed inside the vacuum vessel, analyses and design of an efficient shielding from the electro-magnetic radiations foreseen during the operation of the test facility. All this contributed towards the success in the set-up of the test facility which is now in operation. The thesis is structured as follows:Chapter 1 and 2 are introductory chapters on the present energy scenario in the world, the role of the thermo-nuclear fusion and the main fusion experimental device called ITER. The requirement of additional heating systems in ITER along with the description of Neutral beam injection (NBI) system and relevant ion sources (SPIDER, ELISE and NIO1) are presented in these chapters.Then, the thesis is divided into two main parts: Part 1 – From Chapter 3 to Chapter 6 - describes my work on the power transfer efficiency to the plasma of the inductively coupled radio frequency ion sources. Part 2 – From Chapter 7 to chapter 10 - summarizes first the aim of the HVRFTF then reports my contribution to its design and set-up.Lastly, the overall conclusion highlighting the most significant results obtained from the research described in both the parts of the thesis is discussed and a further possible research activity is highlighted for the future work. Throughout the journey of the PhD, I have had the opportunity to grow and acquire different research competences ranging from conceptual studies, modeling activities, practice on several numerical codes and also experimental work, in an international context." @default.
• W2908219098 created "2019-01-11" @default.
• W2908219098 creator A5018581412 @default.
• W2908219098 date "2018-11-28" @default.
• W2908219098 modified "2023-09-24" @default.
• W2908219098 title "Studies and Experimental Activities to Qualify the Behaviour of RF Power Circuits for Negative Ion Sources of Neutral Beam Injectors for ITER and Fusion Experiments" @default.
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