Theory Weekly Highlights for August 2011

August 26, 2011

An improved model for the radial wave number in TGLF based on the spectral average wave number has resulted in a much better agreement between TGLF and GYRO toroidal stress and the fluxes when both a parallel and a Doppler shear are present. This new model was used in TGLF plus NEO simulations of particle, energy, and momentum transport in the XPTOR code for a DIII-D discharge with a torque scan. This is the most complete multi-moment multi-species simulation ever done with TGLF and the first time that NEO has been used in XPTOR. The predicted density, temperature and toroidal rotation profiles in the core were in good agreement with the data for the unbalanced neutral beam phase of the simulated discharge with high torque in the direction of the plasma current. The balanced beam phase of the same discharge had a predicted carbon toroidal rotation that was somewhat below the data but had a similar shape. The shear in the diamagnetic velocities has not yet been fully integrated into TGLF and is known from recent GYRO simulations to be an important source of toroidal stress.

August 19, 2011

A NIMROD simulation of an Ohmic DIII-D discharge with n = 1 magnetic perturbations applied with 1 kA of C-coil current finds amplification of the 3/1 island and a reduction in edge density. The simulation agrees with measurements made by a fast probe extending across the 3/1 island in the plasma edge showing lower density at the island O-point than the X-point, as well as reversal of the sign of poloidal electric field between the X- and O-points. Both the density and poloidal electric field responses exhibit an m = 6 poloidal mode number in the NIMROD simulation, rather than the m = 3 of the applied magnetic perturbations.

Dr. Wenfung Guo of ASIPP-Hefei arrived at GA to start a 6-month visit to collaborate on the IMFIT integrated modeling project and Dr. Srinivasan Radhakrishnan of IPR-India arrived at GA for a 1-month visit to collaborate on 3D equilibrium analysis.

August 12, 2011

A fully three-dimensional, nonlinear plasma response to an imposed non-axisymmetric field has been calculated using M3D-C1. The calculation obtained the saturated, non-axisymmetric equilibrium of DIII-D discharge #126006 with an imposed n=1 I-coil field. The plasma model included thermal conductivity, viscosity, and Spitzer resistivity. Future runs will include two-fluid plasma rotation. It is known that nonlinear effects may be important in calculations of non-axisymmetric equilibria even when the applied fields are small relative to the total field, due to the strong resonant response of the plasma, especially at high beta. This nonlinear capability, now proven, will therefore allow more accurate determination of the plasma response. Furthermore, this capability opens up the possibility of quantifying the effect of non-axisymmetric equilibrium perturbations on instabilities such as peeling-ballooning modes.

August 05, 2011

Micah Buuck, a National Undergraduate Fellowship (NUF) student working in the GA Theory Group, has significantly enhanced and generalized a collection of PYTHON classes and methods originally contributed to the GACODE project by Luc Peterson (PPPL). These tools simplify and unify the reading, plotting and analysis of data from NEO, GYRO, TGYRO, as well as profile input data as generated by the PROFILES_GEN tool. In addition to the classes and methods which can be used to make custom plots (using MATPLOTLIB and NUMPY), user-level routines are also supplied which can provide summary plots for all codes easily from the command line.

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