Gyrokinetic simulations of the effect of negative magnetic shear on trapped particle drift instabilities
- Univ. of California, Los Angeles, CA (United States)
- Princeton Univ., NJ (United States)
Recent experimental results have shown that significant improvements in tokamak plasma confinement axe achievable in plasma configurations with negative magnetic shear. Here, we investigate the effects of local negative shear on anomalous thermal and particle diffusivities using a fully nonlinear gyrokinetic particle model in field-line-following coordinates including the effects of self-generated shear flows and proper toroidal periodicity. This model includes the nonadiabatic electron density response due to trapped electron dynamics. Trapped electrons use full dynamics and require only a factor of five reduction in timestep, with T{sub i} = T{sub e}. We use parameters from Enhanced Reverse Shear (ERS) discharges in TFTR and initialize the simulations with the local parameters before, during and after the transition from {open_quotes}RS{close_quotes} (regular transport) to {open_quotes}ERS{close_quotes} (improved confinement). The trapped electron gradient-driven drift instability is most strongly affected by negative shear and we present results of the saturation dynamics, quasi-steady state thermal and particle diffusivities and radial correlation lengths from the nonlinear simulations. Results from an alternative approach for modeling the electron response in toroidal geometry, based on the cut-off scheme, will be compared with those from the model presented above (where trapped particles use full dynamics and passing particles axe adiabatic). This method treats particles with a fast parallel velocity, v{sub {parallel}} > v{sub c}, as adiabatic, while slower particles use full dynamics.
- OSTI ID:
- 489383
- Report Number(s):
- CONF-960354-; TRN: 97:011524
- 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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