A study of tearing modes via electron cyclotron emission from tokamak plasmas

The tearing mode is an important resistive magnetohydrodynamic (MHD) mode. The magnetic island structure which it nonlinearly produces can degrade the plasma confinement and reduce fusion reactions. This thesis studies several tearing mode problems from both theoretical and experimental points of view.; A major part of this thesis is to demonstrate that Electron Cyclotron Emission (ECE) is an excellent diagnostic for studying an MHD mode structure and its properties in a tokamak plasma. It is shown that an MHD mode can be detected from the electron temperature fluctuations measured by ECE.; The ECE fluctuation phase profile indicates the magnetic island deformation due to the combination of sheared flow and viscosity. A model is presented to relate qualitatively the observed phase gradient to the local magnetic field, flow velocity shear and viscosity in a 2D slab geometry, using an ideal Ohm's law and the plasma momentum equation including flow and viscosity. Numerical solution of the resultant Grad-Shafranov-like equation shows that the experimentally observed value of the phase gradient can be obtained under realistic parameters for the shear in the flow velocity and viscosity.; The tearing mode stability parameter, Delta', can be measured from the ECE fluctuation amplitude profile [Ren et al., Phys. Plasmas 5, 450 (1998)]. A fit function which has Delta' as one of the fitting parameters is derived for the ECE fluctuation amplitude profile. The theoretical function is then fitted to the experimental data from the Tokamak Test Fusion Reactor. The obtained values of Delta' for 3/2 and 4/3 modes are clearly negative. These results represent the first direct determination of this key tearing mode parameter from internal plasma diagnostics.; Also presented is a new approach to the tearing mode stability boundary and saturation level, using the "almost ideal MHD" constraint [Ren et al., Phys. Plasmas 5, 2574 (1998)]. The numerical results show that the obtained linear stability boundary is the same as that obtained from Delta'-theory [Furth et al ., Phys. Fluids 6, 459 (1963)] and the saturation level is smaller than that of White et al. [Phys. Fluids 20, 800 (1977)].