Turbulence-driven Current Proved for the First Time in EAST Recent Experiment

ASIPP research team published their work in the journal of Physical Review Letter.

How to confine the high temperature ball of plasma at the core of Tokamak facility is an essential and key problem fusion scientists have to tackle. And the plasma current is considered key to high performance confinement. Turbulence is theoretically predicted to generate a drive force to modify the current, However, which has never been observed in tokamak experiments.

During the past campaign of EAST that has realized long pulse plasmas operation with a super high electron temperature over 100 minions Celsius, We observed something that excited them.

The real time data from the experiment showed a modulation of plasma current when electron temperature gradient went up over threshold.

Moreover, as the turbulence increased, the team observed that turbulence-driven current flew into the opposite direction of bootstrap current, which enabled the identification of these two types of current.

In addition to direct observation during the experiment, scientists also bring in gyro-kinetic simulation for further help.

The calculation told scientists the turbulence observed during the experiment was actually electron temperature gradient mode (ETG), by which a residual stress was generated to drive the turbulent current. Then kink mode was triggered leading to the formation of self-regulation among the turbulence, the turbulence-driven current and the kink mode, which worked to keep gradient of electronic temperature at the core stationary.

This physical process was considered by the team as the key to hold stable the long-pulse operation at super-high electron temperature.

ASIPP research team also pointed out effects of the turbulent current on the plasma macroscopic instability and even disruption.

This work was supported by the Youth Innovation Promotion Association Chinese Academy of Sciences under Grant No.2018483 and partly by National Key R&D Program of China (Grant No. 2019YFE03010002).

Figure. Evolution of Turbulence-driven current and Bootstrap current (Image by EAST Team)

                                                                   By ZHOU Shu, LI Erzhong, ZHANG Bin, XU Liqing