Theory Weekly Highlights for May 2008

May 30, 2008

In collaboration with Dr. Y. Liu of Culham Laboratory, a full drift-kinetic version of the MARS-F code based on the kinetic formulation of MHD response has been developed. The kinetic integrals are evaluated in a general toroidal geometry with flow and self-consistently incorporated into the MHD formulation. The energy and momentum fluxes across the plasma surface are expressed in terms of the MHD perturbations. The new kinetic MARS-F has been exercised to show that self-consistent inclusion of the kinetic effect in RWM calculations modifies the eigenfunction and the kinetic stabilization effect is less than that deduced from the perturbation treatment which uses the unperturbed eigenfunction.

May 23, 2008

A high-moment Legendre polynomial numerical solution method for the kinetic response function with pitch angle scattering collisions has been developed that will provide a target for fitting a more accurate collision model for use with TGLF. The new method uses some of the techniques developed for the NEO code. Numerical kinetic response functions can now be generated with a Mathematica program. A new gyro-fluid closure model is being developed in order to fit the gyro-fluid response to the kinetic response. The new closure method should provide a more accurate collision model than to the present model used in TGLF, which was fit to a database of linear growth rates.

May 16, 2008

The drift-kinetic neoclassical code NEO has been upgraded to include the effects of rapid toroidal rotation, which is believed to play an important role in explaining enhanced confinement phenomena, such as the formation of transport barriers. The new formulation, which is based on the theory of Hinton and Wong (PoP 1985, vol 28, p.3082), generalizes the standard neoclassical theory that assumes the diamagnetic ordering, to allow for flow speeds of arbitrary size. Successfully benchmarks of the ion energy flux and momentum flux with analytical theory have been done for the case of a single ion species with adiabatic electrons in the banana regime of collisionality, including the rotation shear. Studies of the neoclassical transport of impure rotating plasmas are in progress.

C. Holland attended the “Multiscale methods for fluid and plasma turbulence: Applications to magnetically confined plasmas in fusion devices'” workshop organized by M. Farge and K. Schneider at the Centre International de Rencontres Mathematiques in Marseille, France, April 21 to 25, where he gave an invited talk titled “Validation of Nonlinear Transport Codes for Core Tokamak Turbulence: Current Status and Future Directions.”

May 09, 2008

A Newton-type scheme has been developed for use with the TGYRO gyrokinetic transport code. The scheme was optimized for use with TGLF, but preliminary tests with GYRO have been successful. Mixed simulations, with calls to TGLF at interior radii and calls to GYRO at outer radii, give roughly converged electron and ion power flows after approximately 10 Newton iterations. We are now in the process of optimizing the method specifically for GYRO calls.

Vincent Chan, Lang Lao and Dave Schissel attended the Fourth US-China Magnetic Fusion Collaboration Workshop at UT-Austin, May 5-6. An overview of the DIII-D five year research plan and status on the IMFIT integrated modeling project were presented. The workshop was attended by 15 Chinese scientists, including the two major fusion facilities, ASIPP and SWIP.

May 02, 2008

The standard quasilinear (Q-L) diffusive heating models implemented in ORBIT-RF and AORSA were benchmarked for the ICRF wave – fundamental minority ion cyclotron harmonic interaction regime in Alcator C-Mod. ORBIT-RF is a Monte-Carlo 5-D ion guiding center code and AORSA is a 2-D full wave code. By not updating the particle orbit after a resonant interaction, the ORBIT-RF result for the heating of a Maxwellian plasma reproduces quantitatively the linear model AORSA result. However, the on-axis spatial profile of absorbed power calculated by ORBIT-RF is increased over that from AORSA; ORBIT-RF calculates Q-L diffusion coefficients using a velocity dependent interaction time, while AORSA assumes it to be constant. This first benchmark result indicates that the interaction time plays an important role and requires a more accurate calculation to improve the accuracy of the power absorption spatial profile. Inclusion of possible interaction of the ions at their banana tips, currently not modeled in ORBIT-RF, may also enhance the accuracy. Robust numerical modeling of this is currently being considered.

These highlights are reports of research work in progress and are accordingly subject to change or modification