### Theory Weekly Highlights for January 2006

##### January 27, 2006

A new collision model for use with the TGLF transport model has been developed. The previous model based on a straightforward moment equation approach to the pitch angle scattering operator did not give accurate results. In the new model, the trapped boundary terms are replaced with simple damping terms. The effective damping rate of these terms is a non-linear function of the ratio of the collision frequency to the electron drift frequency. This model was tested and found to agree very well with the parameter dependence found for GKS runs. Some additional testing is needed but this is looking very encouraging.

Dr. Klaus Hallatschek was awarded the 2005 Rosenbluth Prize in a ceremony at GA on January 26. He subsequently presented a seminar on his work and it's context entitled: “When little whirls make larger whirls, and larger whirls a river …”

##### January 20, 2006

Two new collaborative technologies - SharedAppVNC and Multicursor Window Manager - were installed in the DIII-D control room and demonstrated to physics staff. Multicursor allows multiple users to control the display wall simultaneously from their own stations, as opposed to the display wall console. SharedAppVNC allows users to share selected windows with the display wall or with other users, instead of their entire desktop. Further details are available at: http://shared-app-vnc.sourceforge.net Both SharedAppVNC and Multicursor Window Manager were developed as part of the National Fusion Collaboratory and will be used in the upcoming DIII-D run campaign to support plasma operations.

John M. Greene received the 2006 AMS Leroy P. Steele Prize, one of the highest distinctions in mathematics. The prize was awarded by the American Mathematical Society on January 13, 2006, in San Antonio, Texas. John shared the prize with three co-authors for their 1974 joint paper: “Korteweg-deVries equation and generalizations. VI. Methods for exact solution”, (Commun. Pure and Applied Math., 27, 97, 1974). See the announcement at: http://fusion.gat.com/theory/announcements/John_Greene.pdf

##### January 13, 2006

Recent studies of the effects of plasma shaping on the E x B shear quench rule found the quench point varies considerably from the rule γE/γmax = 2.0. In previous shifted circle studies, it was found that the E x B shear quench point was robustly at γE/γmax = 2.0 for both ITG and TEM dominated cases. In the GYRO simulations with kinetic electrons using the Miller equilibrium model for real geometry, however, it was found that less E x B shear is needed to quench the transport for high elongation. The E x B shear quench point also varies with aspect ratio, A, at fixed plasma elongation and triangularity. Here, the quench point follows an offset linear dependence on A with low aspect ratio needing less E x B shear to quench the transport. A power law fit of (γE/γmax)quench ~ A0.65 fits the GYRO results equally well over a range of 2 < A < 4. A summary of the variation in quench point with elongation and aspect ratio can be seen at: http://fusion.gat.com/theory/weekly_highlights/attachments/quench_point.pdf

Paul Garabedian from the Courant Institute of NYU visited from January 5 through 12 to discuss various issues with GA and DIII-D staff on confinement in 3D configurations, with a focus on the issues of alpha confinement in ITER.

##### January 06, 2006

In a burning plasma, the alpha-particle population will be localized within the core (r/a < 0.6), whereas turbulence levels are generally weak for r/a < 0.4 and increase towards the edge. GYRO simulations in the vicinity of r/a=0.5, where an overlap of alpha particles with ITG turbulence occurs, indicate that for ITER-like plasmas the turbulent alpha fluxes (both density and energy) can be as strong (per particle) as the turbulent D-T fluxes. This violates the common wisdom that the effects of turbulence on large-gyroradius alphas are averaged out. This research ultimately indicates that in the outer band, 0.4 < r/a < 0.6, alpha particle modeling codes may need to account for profile modification due to interaction with ITG turbulence.

**Disclaimer**

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

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