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Edge stability and transport control with resonant magnetic perturbations in collisionless tokamak plasmas


A critical issue for fusion-plasma research is the erosion of the first wall of the experimental device due to impulsive heating from repetitive edge magneto-hydrodynamic instabilities known as 'edge-localized modes' (ELMs). Here, we show that the addition of small resonant magnetic field perturbations completely eliminates ELMs while maintaining a steady-state high-confinement (H-mode) plasma. These perturbations induce a chaotic behaviour in the magnetic field lines, which reduces the edge pressure gradient below the ELM instability threshold. The pressure gradient reduction results from a reduction in the particle content of the plasma, rather than an increase in the electron thermal transport. This is inconsistent with the predictions of stochastic electron heat transport theory. These results provide a first experimental test of stochastic transport theory in a highly rotating, hot, collisionless plasma and demonstrate a promising solution to the critical issue of controlling edge instabilities in fusion-plasma devices.

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Figure 1: ELM response to an applied magnetic perturbation.
Figure 2: Changes in the ELM response with increasing magnetic perturbation levels.
Figure 3: The value of the safety factor at the 95% magnetic flux surface (q95) influences the ELM response to the RMP.
Figure 4: Changes in the edge-plasma profiles with various magnetic perturbation levels.
Figure 5: ELM stability diagram.
Figure 6: Contour plot of the magnetic perturbation spectrum.

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We would like to thank R. J. La Haye for pointing out that magnetic shielding due to edge-plasma rotation may be a significant effect in these experiments. This work was supported by the US Department of Energy under DE-FC02-04ER54698,W-7405-ENG-48, and DE-FG02-04ER54758.

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Correspondence to Todd E. Evans.

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Evans, T., Moyer, R., Burrell, K. et al. Edge stability and transport control with resonant magnetic perturbations in collisionless tokamak plasmas. Nature Phys 2, 419–423 (2006).

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