### Theory Weekly Highlights for August 2007

##### August 31, 2007

A new postdoctoral fellow, Thomas Fouquet, has arrived to participate in the SciDAC Steady-state Gyrokinetic Transport Code (SSGKT) project under the supervision of Jeff Candy. Thomas will work together with Drs. Kinsey, Staebler, Waltz and Candy on this project, enhancing the synergy between the TGLF and SSGKT efforts.

Jeff Candy gave a talk, “Status of Gyrokinetic Transport Modeling”, at the 2007 Rosenbluth Summer School in La Jolla CA.

##### August 24, 2007

Clemente Angioni is visiting GA for three weeks from the Max Planck Institute and ASDEX to work with Ron Waltz and Jeff Candy on turbulence simulation. He is also providing his extensive expertise on sawtooth modeling to the MHD group.

##### August 17, 2007

Numerical analysis of guiding center drift orbits using ORBIT-RF qualitatively agrees with the analytic stochasticity onset criterion in phase space obtained from the standard linear one-step mapping equation. For the analytic criterion, the orbit theoretically transitions from adiabatic to stochastic behavior when the stochastic onset parameter S=1. S is related to the product of the perturbation amplitude and the change in phase from each rf kick. In addition to the wave amplitude, S depends on finite parallel wavelength, k*, the finite Larmor radius, magnetic field inhomogeneity, pitch angle, and ion energy. All these parameters vary along the orbit in a realistic simulation and are expected to impact the threshold quantitatively. For fundamental harmonic heating, it is found that the threshold wave amplitude satisfying S≥0.5 is sufficient for onset of a stochastic trajectory, suggesting that the required threshold electric field might be smaller than the analytic prediction. A more rigorous criterion for the onset of stochasticity is being developed, which will be used to modify the quasi-linear model for wave interactions with energetic particles.
== August 10, 2007 ==
Jeff Candy won a 2008 “Anniversary Professorship” at Chalmers University in Gothenburg, Sweden. This will involve two visits of about 3 weeks per visit in 2008. Dr. Candy will be working with Tunde Fulop and Hans Nordmann on neoclassical and turbulent transport analyses for ITER. The honor is given annually in order to foster collaboration between Chalmers University and leading researchers from around the world. Each year, between three and five such awards are given in diverse areas of science and engineering.
Dr. K.I. You of Korea National Fusion Research Center visited GA for two weeks to collaborate on KSTAR equilibrium reconstruction and ideal stability modeling using the EFIT and the GATO codes.
== August 03, 2007 ==
Two student interns have recently joined the Data Analysis Applications Group to help with Web related projects. They are working on improving and organizing the web content to provide a cleaner web structure and a consistent user experience for GA fusion and DIII-D personnel. Additionally, they will be assisting in moving away from proprietary Microsoft ASP pages to open-source PHP-based pages. In the process, they have been gaining experience with web scripting languages, web graphics and databases.
Dr. Morrell Chance is visiting GA from PPPL for two weeks to work with Theory staff on the Normal Mode Approach code for studying active feedback.
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**Disclaimer**

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