Core transport barriers predicted by drift wave models with flow shear
- General Atomics, San Diego, CA (United States)
A transport model which includes the suppression of turbulence by sheared E x B rotation has been successful in reproducing much of the phenomenology of the L/H transition. The VH-mode naturally follows from the model at high power. Other enhanced confinement modes with core transport barriers have also been predicted by the model. If the power deposition is strongly peaked at the center and the recycling is low at the edge, a transport barrier can form in the core and not at the edge. These predicted model discharges axe similar to the recently discovered enhanced core confinement regimes with weak or negative central magnetic shear. The previous model has been extended to include much more of the physics of drift wave energy, particle, and momentum transport. A rather comprehensive local quasilinear dispersion theoretic model fitted to gyrofluid nonlinear simulations as well as a simpler formula based model axe used to treat all transport channels. These models are applied to DIII-D negative central shear discharges. The predicted power threshold for the bifurcation to an interior transport barrier is lower if the density profile is more peaked which is suggestive of the pellet enhanced (PEP) confinement modes. Toroidal momentum injection counter to the current is predicted to be more favorable than co-injection. Negative central magnetic shear and finite Shafranov shift is found to lower the power threshold, but is not essential to the bifurcation caused by E x B rotational shear stabilization. Negative magnetic shear is essential to avoid MHD instabilities which would otherwise limit the pressure gradient in the transport barrier. The predicted scaling of the power threshold for core transport barriers to reactor scale devices like ITER at smaller relative gyroradius depends crucially on whether the E x B rotational shear is induced diamagnetically or by toroidal momentum input.
- OSTI ID:
- 489367
- Report Number(s):
- CONF-960354-; TRN: 97:011508
- Resource Relation:
- Conference: International Sherwood fusion theory conference, Philadelphia, PA (United States), 18-20 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 international Sherwood fusion theory conference; PB: 244 p.
- Country of Publication:
- United States
- Language:
- English
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