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Rotating Plasma Finding is Key for ITER


Tokamak turbulence showing inward-propagating streamers from normalized electrostatic potential fluctuation (red is positive and blue is negative fluctuation). Simulations at NERSC using the XGC1 gyrokinetic code show that the inward propagation of turbulence power from tokamak plasma edge brings the plasma momentum with it.

Key Challenges: Multiscale plasma simulation over the entire volume of a realistic tokamak device are possible only with petascale computing resources. 

Why it Matters:  Stabilization of tokamak plasma by external rotation sources has been demonstrated experimentally, but ITER is too large to have an external rotation source so it’s important to understand how to stabilize it via intrinsic rotation.  The origin of ntrinisic rotation is not well understood but ITER success may depend on it.

Accomplishments:  The SciDAC XGC1 gyrokinetic code was used to model relevant multi-scale physics over the entire plasma volume of the DIII-D fusion reactor.  Findings point to the plasma edge as a source of rotation and strongly support the model of turbulence driven intrinsic torque as the origin of intrinsic rotation.  The results suggest that ITER could achieve adequate spin up by utilizing this understanding.  

NERSC Contribution:  Simulations resulting in the publication below were performed on Hopper using over 10 million hours on about one-half of the system.  It is one of several achievements made by this group in 2012 using NERSC resources.  During AY2012, the repo consumed 78M hours (100% of allocation), running 22,200 jobs total, with 84% at concurrency of 16k cores or above and 48% at 64k or above.

Investigators: C. S. Chang (PPPL)

More Information:   C.S. Chang, et al., “Physics of intrinsic rotation in flux-driven ITG turbulence,” Nucl. Fusion 52 (2012) 063013