Soft x-ray measurement of internal tearing mode structure in a reversed-field pinch

The structure of internally resonant tearing modes has been studied in the Madison Symmetric Torus reversed-field pinch with a soft x-ray detector system consisting of an imaging array at one toroidal location and several detectors at different toroidal locations. The toroidal mode numbers of m = 1 structures are in the range n = -5, -6, -7. The modes propagate with phase velocity v = 1--6 x 106 cm/s, larger than the diamagnetic drift velocity vd ∼ 5 x 105 cm/s. Phase locking between modes with different n in manifested as a beating of soft x-ray signals which is found to be strongest near the resonant surfaces of the modes (r/a = 0.1 -- 0.5). 15 refs., 5 figs