Single layer metamaterial lens with frequency dependent focus for efficient NTM control in fusion plasmas -

Abstract

Fusion energy is achieved on Earth through heating deuterium and tritium, the two types of hydrogen atoms, which are combined, to very high temperatures (100 million degrees Celsius). At 100 million degree Celsius, the plasma, ionized gas, would be moving very fast, in a way that keeps its density very low if it is left alone, hence decreasing the number of collisions. Huge Electromagnets were used to keep the density of the plasma high enough for sufficient collisions to occur, leading the plasma to circulate within a ring-shaped vessel called the Tokamak. Yet, Magnetic islands naturally form in the plasma, mostly in low current regions, preventing plasma confinement. Electron Cyclotron Emission (ECE) measurements provide data about the location of Neoclassical Tearing modes (NTMs) in Plasma. Collected signals are then modulated and passed to gyrotrons, which emit waves targeting magnetic islands. Oblique ECE radiometry applied to the modulation of Electron Cyclotron Current Drive (ECCD) proved to be successful for NTM stabilization in fusion Plasma. To achieve efficient NTM control in plasma, the data must be collected from the radiometer with high resolution, and hence specifying locations of magnetic islands in the Plasma accurately guiding the alignment between waves emitted by gyrotrons through ECCD and magnetic islands. Lenses with frequency dependent focus were proposed in the literature to replace the Gaussian lens used to focus emissions from the plasma to the radiometer. The proposed design was based on layer capacitive patched and inductive wire grids, which appeared to be complex in design and manufacture. In this thesis, single layer metamaterial lenses with frequency-dependent focal points are investigated to replace the design in the literature, leading to high resolution temperature profile measurements . Two designs are proposed, and in the two designs, the surface of the single layer lens is divided into zones where each zone is optimized for a specific frequency and provides a spec