Role of flow shear in enhanced core confinement regimes

Abstract

The importance of the ExB fla shear in arioi s enhanced confinement regimes is discussed in terms of the turbulence suppression criterion in toroidal geometry. This criterion is then further generalized to include the poloidal angle dependence of the equilibrium electrostatic potential. The implication of the recently observed in-out asymmetry in the fluctuation behavior in DIII-D VH-mode is discussed. DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-

Effect of the radial electric field on the fluctuation-produced transport in the H-1 heliac

“…Thus, our results do not contradict the E r shear suppression models [2][3][4][5] in the 'quiescent' high mode. It should be noted that fast oscillations in the radial electric field before the transition to the H-mode (figures 11 and 12) could reduce the effective shearing rate, as discussed by Hahm et al [32].…”

E×B shearing rate in quasisymmetric plasmas

“…30 The expression for the EϫB nonlinear term in flux coordinate is given by Frieman and Chen. 31 The two-point correlation evolution equation is then derived following the standard procedure 32 of symmetrization with respect to ( 1 ,␣ 1 ,␤ 1 ) and ( 2 ,␣ 2 ,␤ 2 ) followed by ensemble average,…”

“…Note that there is some evidence of larger EϫB shearing rate at the bad curvature side of tokamaks. 9,30 We can also write the EϫB shearing rate in terms of the poloidal flux d p ϵd and the magnetic safety factor q ϵ1/,…”

Symmetry breaking effects of density gradient on parallel momentum transport: A new ρs* effect

“…1 Mean E Â B shear, be it selfgenerated like zonal flow shear or by external radial electrode biasing, is well known to suppress turbulence. [2][3][4][5] Toroidal rotation couples dynamically to the E Â B shear and thus affects the turbulence suppression mechanism, which is believed to be important for the L-H transition as well as the formation of internal transport barriers (ITBs). 6 Toroidal rotation is also helpful in suppressing certain types of harmful magnetohydrodynamic (MHD) instabilities, such as resistive wall modes (RWM) (Refs.…”