(TH/1-2) A Comprehensive Theory-Based Transport Model

G.M. Staebler1), J.E. Kinsey2), R.E. Waltz1)
 
1) General Atomics, San Diego, California, United States of America
2) Lehigh University, Bethlehem, Pennsylvania, United States of America

Abstract.  A new theory based transport model with comprehensive physics (trapping, general toroidal geometry, finite beta, collisions) has been developed. The core of the model is the new trapped-gyro-Landau-fluid (TGLF) equations which provide a fast and accurate approximation to the linear eigenmodes for gyrokinetic drift-wave instabilities (trapped ion and electron modes, ion and electron temperature gradient modes and kinetic ballooning modes). This new TGLF transport model removes the limitation of its predecessor GLF23 and is valid for the same conditions as the gyrokinetic equations. A theory-based philosophy is used in the model construction. The closure coefficients of the TGLF equations are fit to local kinetic theory to give accurate linear eigenmodes. The saturation model is fit to non-linear turbulence simulations. No fitting to experiment is done so applying the model to experiments is a true test of the theory it is approximating. The TGLF model unifies trapped and passing particles in a single set of gyrofluid equations. A model for the averaging of the Landau resonance by the trapped particles makes the equations work seamlessly over the whole drift-wave wavenumber range from trapped ion modes to electron temperature gradient modes. A fast eigenmode solution method enables unrestricted magnetic geometry. Electron-ion collisions and full electromagnetic fluctuations round out the physics. The linear eigenmodes have been benchmarked against comprehensive physics gyrokinetic calculations over a large range of plasma parameters. The deviation between the gyrokinetic and TGLF linear growth rates averages 11.4% in shifted circle geometry. The transport model uses the TGLF eigenmodes to compute quasilinear fluxes of energy and particles. A model for the saturated amplitude of the turbulence completes the calculation. The saturation model is constructed to fit a large set of nonlinear gyrokinetic turbulence simulations. The TGLF model is valid in new physical regimes that GLF23 was not. For example, the low aspect ratio spherical torus which has both a high trapped fraction and strong shaping of magnetic flux surfaces. The TGLF model is also valid close to the magnetic separatrix so the transport physics of the H-mode pedestal region can be explored.
* Work supported by US DOE under DE-FG03-95ER54309 and DE-FG02-92ER54141.

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