Theory Weekly Highlights for February 2008

February 29, 2008

A new analysis of the iteration algorithm used in most equilibrium codes for finding axisymmetric plasma equilibria shows that linear axisymmetric stability of the equilibrium obtained is closely related to the numerical stability of the iterations. The equilibrium boundary conditions are generally specified by points where the flux is fixed; these are then regarded as representing an ideal conductor in the physical stability problem. The analysis showed that the iteration process is equivalent to solving the ideal axisymmetric stability problem with a slightly increased current density profile where the margin of increase is related to the iteration convergence rate. The numerical procedure then mimics the amplification or reduction of small errors in force balance at each iteration step in the same way as the linearized physical forces. The use of fictitious currents inside the plasma to keep the numerical iterations stable in some schemes is equivalent to axisymmetric feedback of the physical system.

February 22, 2008

A TGLF website at http://fusion.gat.com/theory/TGLF is being set up, patterned after the GYRO site http://fusion.gat.com/theory/Gyro which has over 6000 hits to date. The site presently has a one page description, a list of publications, and a link to the transport simulation database used to benchmark TGLF. A download and release page will soon be established. Trial versions have been privately distributed to GA collaborators at PPPL, Culham-UK, and IPP-Garching.

February 15, 2008

The TGYRO gyrokinetic transport solver now has the ability to call the TGLF model in addition to GYRO to compute particle and energy fluxes. This flexibility will be used to speed up local TGYRO calculations near threshold and in other situations where the GYRO fluxes are too expensive to be practical. TGYRO is being developed as part of the SciDAC-funded Steady-State Gyrokinetic Tranport Code (SSGKT) project. A new URL for the GYRO code home page is provided at http://fusion.gat.com/theory/gyro with a link to the TGYRO transport module at http://fusion.gat.com/theory/tgyro

February 08, 2008

As part of the SWIM project for self-consistent coupling of ORBIT-RF and the 2-D full wave code AORSA, the spatial local power absorption (Pabs) profile from ORBIT-RF/AORSA was shown to be in qualitative agreement with that from AORSA and CQL3D. The comparison was a simulation of C-Mod hydrogen minority ICRF heating experiments and agreement was obtained when the interactions of ions with multiple wave modes in different spatial locations are realistically modeled. A code was written to map the AORSA wave electric fields in cylindrical coordinates to Boozer coordinates needed for the ORBIT-RF quasi-linear operator. Since AORSA does not provide a decomposition of the (toroidal n, poloidal m) spectrum required to decide the local resonance locations, the local parallel component of the wavevector k// is modeled using a random number generator with either a uniform or gamma distribution probability function. Preliminary comparison results indicate that the modeling using the gamma distribution yields better agreement with AORSA/CQL3D. This is attributed to the fact that antenna code calculates a weighted toroidal mode spectrum peaked around n = 10. However, ORBIT-RF/AORSA produces quantitatively larger Pabs than Pexp and AORSA/CQL3D since the spatial averaging of the full wave fields over a perpendicular wavelength, consistent with a quasilinear formulation, is ignored. Simulations with spatially averaged AORSA wave fields with k// modeled with a gamma distribution are in progress.

February 01, 2008

CERAUTO analysis has been run routinely on plasma shots since near the beginning of operations this year. The automated process also includes rerunning theZIPFIT, IMPCON, and AutoONETWO codes with CERAUTO data. The analysis is performed in the late evening on the Star cluster, and data for the day's shots is available in MDSplus by the next morning.

Paul Parks attended the DOE/OFES-sponsored Plasma Jet Workshop held at LANL, January 24-25, 2008 and gave a 40 minute talk entitled: ‚ÄúPlasma Jet Driven Magneto-Inertial Fusion: Ignition considerations‚ÄĚ.



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