Modelling of a plasma break-down for the SMART tokamak

Abstract

Achieving controlled nuclear fusion on Earth could be a decisive step on the quest towards green energy production since it would bring a virtually renewable energy source without CO2 emissions. The Plasma Science and Fusion Technology group of the University of Seville is currently designing a magnetic fusion device, a spherical tokamak for controlled nuclear fusion research, called SMall Aspect Ratio Tokamak (SMART). This thesis will model the first phase of the initiation of a tokamak (tokamak start-up), the break-down phase, in which the fuel will transition from the gas state to the plasma state, making use of the Fiesta toolbox. The fundamental of tokamak physics and tokamak start- up will also be reviewed. The current waveforms of the SMART coilset have been optimized to achieve the desired plasma equilibrium and allow the break-down of the pre-fill gas by reducing the stray poloidal magnetic field and maximizing the loop voltage induced by the inductor solenoid. Several criteria have also been applied to test the feasibility of the break- down phase, such as the Paschen’s break-down curve, the estimation of the avalanche time, and the calculation of the connection length. The electric potential gained by the electrons as they follow the magnetic field lines has been computed to estimate where the gas will break-down. Break-down of the gas without the use of any auxiliary heating method has been achieved, lasting few milliseconds for gas pressures about 10−4Torr.