Tearing mode structure in the DIII-D tokamak through spectrally filtered fast visible bremsstrahlung imaging

Time evolved measurements of the detailed 2D poloidal structure of rotating tearing modes in the DIII-D tokamak are obtained for the first time using spectrally filtered fast imaging of broadband visible bremsstrahlung emission (N B). Measurements are made along 256 × 256 different sightlines and show excellent agreement with simulations assuming a rotating helical m/n = 2/1 island structure superimposed on the equilibrium N B profile. The method described here is capable of imaging with high resolution the structure of coherent oscillations in the core of current and next-step fusion plasma experiments such as ITER and can be applied to virtually any mode with a finite perturbed N B and frequency in the laboratory frame provided sufficient signal level and detector bandwidth are available.