Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma

TLDR

Fluctuation reduction asymmetry is linked to flux expansion and magnetic field pitch, while neutral particle charge exchange damping adversely affects confinement. The study applies a two‑point nonlinear analysis to examine turbulence suppression by E×B and parallel flow shear in an arbitrary‑shaped finite‑aspect‑ratio tokamak. Only E×B flow shear suppresses flute‑like fluctuations, independent of rotation direction, making it relevant for both VH core and H‑mode edge plasmas. Citation: Plasmas 1, 2940 (1994).

Abstract

The suppression of turbulence by the E×B flow shear and parallel flow shear is studied in an arbitrary shape finite aspect ratio tokamak plasma using the two point nonlinear analysis previously utilized in a high aspect ratio tokamak plasma [Phys. Plasmas 1, 2940 (1994)]. The result shows that only the E×B flow shear is responsible for the suppression of flute-like fluctuations. This suppression occurs regardless of the plasma rotation direction and is, therefore, relevant for the very high (VH) mode plasma core as well as for the high (H) mode plasma edge. Experimentally observed in–out asymmetry of fluctuation reduction behavior can be addressed in the context of flux expansion and magnetic field pitch variation on a given flux surface. The adverse effect of neutral particles on confinement improvement is also discussed in the context of the charge exchange induced parallel momentum damping.