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 (NB). 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 NB 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 NB and frequency in the laboratory frame provided sufficient signal level and detector bandwidth are available.