Rotational and magnetic shear stabilization of magnetohydrodynamic modes and turbulence in DIII-D high performance discharges

Abstract

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Physics of advanced tokamaks

“…In linear theory, the decorrelation rate can be approximated by the maximum linear growth rate, ymax (Waltz 1995). The stabilization of microturbulence by ExB sheared flow is consistent with reduced e t t e transport observed in H-mode, reduced transport observed in VH-mode and high Pi, and the reduced core transport observed in NCSERS discharges (Burrell 1997;Lao 1996; LA Haye 1995;Synakowski 1997a;1997b;Beer 1997). Although the experimental observations are generally consistent with this paradigm, a General Atomics Report GA-A22704number of questions remain which indicate additional physics mechanisms are important or the need for more complete fully non-linear treatment of microturbulence stabilization by sheared flow.…”

“…First, there is a spatial correlation between the region where % x~ > ymax and the region of reduced transport as is ilfstrated in Fig. 9 (Lao 1996;Rice 1996;Levinton 1996;Rewoldt 1996Rewoldt , 1997Schissel 1996;Greenfield 1997;Burrell 1997). It is also noted by a number of authors, that modeling of the transport by gyrokinetic and gyrofluid calculations can reproduce the observed temperature profiles, but only if the sheared ExB flow is included (Waltz 1996).…”

“…It is also noted by a number of authors, that modeling of the transport by gyrokinetic and gyrofluid calculations can reproduce the observed temperature profiles, but only if the sheared ExB flow is included (Waltz 1996). In DIII-D H-mode discharges with negative or weak central magnetic shear, the ion thermal transport is observed to be near neoclassical values across the entire discharge cross section (Lao 1996;Lazarus 1996aLazarus , 1997bGreenfield 1997) and in these discharges, > y?,"", across the same region, the entire discharge, as shown in Fig. 10.…”

“…Dashed trajectory is for an Gmode NCS discharge, solid trajectory is for H-mode NCS discharge (Lao 1996). Insets are exp.…”

“…In DIII-D NCS discharges the internal transport barrier is observed clearly in the ion temperature and toroidal rotation profiles. With an increase in power, and strong negative central shear, a clear barrier is seen in the electron density, and sometimes a modest reduction in electron transport (factor of 2 to 5 ) is calculated (Strait 1995b;Rice 1996aRice , 1996cLao 1996;Greenfield 1997;Schissel 1997). In Tore Supra LH heated discharges, the transport barrier is seen very clearly in the electron temperature only, with a decrease of almost two orders of magnitude in the central electron transport (Litandon 1996~).…”