Reduced critical rotation for resistive-wall mode stabilization in a near-axisymmetric configuration |
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Authors: | Reimerdes H Garofalo A M Jackson G L Okabayashi M Strait E J Chu M S In Y La Haye R J Lanctot M J Liu Y Q Navratil G A Solomon W M Takahashi H Groebner R J |
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Institution: | Columbia University, New York, New York 10027, USA. |
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Abstract: | Recent DIII-D experiments with reduced neutral beam torque and minimum nonaxisymmetric perturbations of the magnetic field show a significant reduction of the toroidal plasma rotation required for the stabilization of the resistive-wall mode (RWM) below the threshold values observed in experiments that apply nonaxisymmetric magnetic fields to slow the plasma rotation. A toroidal rotation frequency of less than 10 krad/s at the q=2 surface (measured with charge exchange recombination spectroscopy using C VI) corresponding to 0.3% of the inverse of the toroidal Alfvén time is sufficient to sustain the plasma pressure above the ideal MHD no-wall stability limit. The low-rotation threshold is found to be consistent with predictions by a kinetic model of RWM damping. |
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