ECM Observed to Provide Continuous Transport in Long-pulse H-mode Plasma

An elctronstatic coherent mode (ECM) near the electron diamagnetic frequency (20-90 kHz) is observed in the steep-gradient pedestal region of long pulse H-mode plasma in EAST, using a newly developed dual gas-puff-imaging system and diamond-coated reciprocating probes, and the mode provides a channel for continuous particle and heat exhaust across the pedestal, which is essential for the maintenance of long pulse H-mode plasmas. The research result is recently published in Physical Review Letters. 

In 2012, a record 30-second long pulse H-mode plasma had been achieved in EAST experiment. To explain how to keep long pulse H-mode plasma, Dr Guosheng Xu and his team spent more than one year to study the mechanism in sustaining the long pulse H-mode. They observed ECM, and found that the mode propagates in the electron diamagnetic direction in the plasma frame with poloidal wavelength of ~8 cm, and the mode drives a significant outflow of particles and heat as measured directly with the probes, thus greatly facilitating long pulse H-mode sustainment. The team conclude the electrostatic coherent mode will provide a new approach to long pulse H-mode plasma sustainment. (Zhao Nan reports)