The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition from a nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 in the large helical device. This flow damping and resulting profile flattening are much stronger than expected from the Rechester–Rosenbluth model. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that the flow damping is due to the change in the non-diffusive term of momentum transport.
Plasma heating using fast waves was successfully performed on the Experimental Advanced Superconducting Tokamak (EAST) in the H minority regime in deuterium plasmas at 27 MHz and B
o = 2.0 T. With 1.0 MW of ion cyclotron range of frequency (ICRF) power injected at a line-averaged electron density of 4.0 × 1019 m−3, the electron temperature increased from 1.0 keV to above 2.0 keV and the loop voltage dropped. An increase in the stored energy by 30 kJ was obtained. The first H-mode plasma of 6.4 s was achieved with a combination of lower hybrid wave and ICRF heating. Density pump-out was observed during L-mode discharges at a high electron density of 4.0 × 1019 m−3. In these discharges, re-attachment of the plasma was observed when ICRF power was applied.
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