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Study on the production of a high-power negative ion beam and its photoneutralization for use in Tokamaks

Perrakis Konstantinos

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Summary

In order to heat the plasma confined in a clean energy fusion reactor power plant, like ITER and DEMO, large amounts of energy are required. One method to achieve this is to inject a neutral beam into the plasma. This thesis contributes to the development of a method to create a neutral hydrogen beam through the formation, acceleration and extraction of a negative ion hydrogen beam from a magnetically insulated diode. This work involves modeling the operation of the diode and performing numerical calculations for the acceleration and extraction of the negative ions. The cathode plasma from which the ions are extracted can be produced by laser-cluster interaction, while the concept of magnetic insulation is used to separate negative ions from electorns. An 2-fluid 1-D code in cylindrical geometry describes the spatio-temporal evolution of the ions and the electrons inside the diode. Results from the code are tested against available experimental data from the international literature concerning pulsed-power devices with high current and high energy negative ions, in order to investigate the natural processes of the formation and extraction of the beam. The numerical results of the code are in good agreement with the experimental data using the appropriate physical and the geometrical parameters of the devices. The use of a laser is also proposed as a means to neutralize the negative ion beam with photodetachment, in order to achieve greater efficiency and cut down costs by reusing equipment. The innovation of this work is that while the relative technologies are long-established, they have not been proposed for use in Tokamaks despite the fact that they offer significant advantages compared to others when it comes to plasma heating. The contribution to science is constituted by proving via simulations that the magnetically insulated diode is a device that can produce a high energy and high current negative ion beam.

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