Theory Weekly Highlights for October 2011

October 28, 2011

Recent GYRO simulations have likely ruled out symmetry breaking induced by the fast ion diamagnetic drift as an explanation of the poloidal shearing observed in ECE images of fast ion-excited Alfvén eigenmodes in DIII-D discharge 142111. The shearing is not predicted by a pure MHD model. Three gyrokinetic codes (GYRO, GTC, and TAEFL) correctly predict this shearing near the mode peak, but sometimes disagree on the shearing direction in the tail. The GYRO simulations show that the shearing magnitude of a TAE, as represented by the phase shift between the interior simulation domain and the mode peak, does not change even as the fast ion population is reduced to the level of near-marginal stability. The findings imply that heating beam profile shape is not as important to the mode structure as previously expected, a prediction that can be tested by comparing on and off axis beam injection cases.

October 21, 2011

Version 5.4 of the ONETWO transport code is ready for public release. All known corrections are in place and regression testing was done. One of the primary additions is the inclusion of the new parallel version of the PNFREYA neutral beam model (see March 11 highlight), and additional enhancements to accommodate the new DIII-D 14 beamlet experimental setup with four individually addressable sources in the 150 degree beam line and two individual sources for the remaining beams. PNFREYA normally runs with 14 parallel processors to efficiently simulate the increased number of Monte Carlo pseudo particles needed to obtain smooth deposition profiles with 14 independent sources. To shield users from the complexities of running the PNFREYA parallel code on a remote machine, an external configuration file was created which is customizable on a per user basis. Fast ion diffusion was added by modifying the birth and deposition profiles using the NUBEAM parabolic diffusion coefficient parameterization. A routine to solve for the steady state fast ion density given the Monte Carlo birth rate of ions is part of this scheme. An update user manual, reflecting the latest updates will be available on the DIII-D WIKI page.

October 14, 2011

Phil Snyder and Gary Staebler attended the 13th International Workshop on H-Mode Physics and Transport Barriers, held in Oxford, UK October 10-12. Dr Snyder gave a presentation on “The EPED Pedestal Model: Model Extensions and Validation,” and Dr. Staebler gave a presentation on “A Deeper Understanding of ExB Velocity Shear Stabilization and the Role of Radial Mode Structure.” The previous week, Dr. Snyder, Dr. Staebler, and Dr. Valerie Izzo attended ITPA Meetings on Pedestal Physics, Transport and Confinement and MHD, respectively.

October 07, 2011

The driver for GENRAY is now implemented as an RF heating and current drive module in the IMFIT framework. GENRAY computes the power deposition and driven current in the plasma by lower hybrid, electron cyclotron, and ion cyclotron RF waves. In the GENRAY configuration file, users can specify the RF model and related variables such as RF frequency and the number of rays. Template input files corresponding to the three different RF models are set up in the template directory. Under IMFIT, the configuration file copies the chosen template file to the working directory, updates the namelist input variables using input variables specified by the user, and runs the GENRAY simulation. Test runs under the IMFIT framework reproduce identical results to those produced from a standalone simulation.

A new computational node, METIS, ( was set up and put into production by the DAAG Group to be dedicated to between shot MDSplus data analysis codes. The server runs a 64-bit CentOS 5.7 operating system and supports IDL analysis via a single node-locked license for 64-bit IDL 8.1. Between shot MDSplus analysis codes that have previously run on the LSF cluster have been ported from HP-UX and 32-bit Linux to 64-bit Linux and are now running in production on METIS, including: Confinement, ECE, Filterscope, NB, Pedestal, Spred, PRAD Quick, etc.

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