Turbulence-driven current first proved in recent EAST experiment

In a recent campaign of Experimental Advanced Superconducting Tokamak (EAST), researchers from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) and their partners managed to prove experimentally, for the first time, the current driven by turbulence, via observed data during the experiment and simulations after. 

The turbulence-driven current, according to the researchers, was also an important factor to sustain the 100 million degrees of electron temperature stationary long-pulse plasma on EAST. Results were published on Physical Review Letters.

How to confine the high temperature ball of plasma at the core of Tokamak facility is a key problem fusion scientists have to tackle. Plasma current is considered key to high performance confinement. Turbulence is theoretically predicted to generate a drive force to modify the current, but this 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 ℃, the researchers 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, they found that turbulence-driven current flew in the opposite direction to the bootstrap current, enabling them to identify the two types of current.

In addition to direct observation during the experiment, they also introduced gyro-kinetic simulation for further help.

The calculation showed that the turbulence observed during the experiment was actually electron temperature gradient mode, through which a residual stress was generated to drive the turbulent current. Then kink mode was triggered to form a self-regulation among the turbulence, the turbulence-driven current and the kink mode, keeping gradient of electronic temperature at the core stationary.

This physical process was considered by the researchers as the key to maintaining stable operation of long pulses at ultra-high electron temperature.

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