### Theory Weekly Highlights for November 2008

##### November 28, 2008

New fusion-gain calculations for solid-liner MTF indicate that gains of over 20 may be achieved if high density FRC plasma can be formed and compressed. From a new model of magnetized target decompression with heavy metal (incompressible) liner/tamper, calculations indicate gains of over 20 can be achieved if a high density (~ 2×10^{18} cm^{-3}) FRC plasma can be formed and compressed. These gains are vey attractive and far superior to the essentially “epsilon” gains possible for Plasma Jet MTF.

Phil Snyder and Emili Belli gave invited talks at the 50th American Physical Society Division of Plasma Physics meeting in Dallas Texas. Snyder present his recent work on “Development and Validation of a Predictive Model for the Pedestal Height”. Belli described her work on “Drift-Kinetic Simulations of Neoclassical Transport”.

##### November 21, 2008

Stability analysis of a DIII-D QH -mode discharge with Edge harmonic Oscillation (EHO) using MARS-F indicates that rotational shear can have both a stabilizing and also a de-stabilizing effect on the edge plasma. For the conventional external kink or resistive kink, when unstable, the effect of rotational shear has been found to moderately stabilizing in the sense of reducing their growth rates. For a stable equilibrium near the marginal stability point of the ideal external kink, a weak ideal instability has been found driven by the rotation shear. In this case, the mode is further destabilized by rotational shear with the computed growth rate proportional to the rotation shear. Many properties of this latter mode suggest that it could correspond to the observed EHO.

##### November 14, 2008

A comparison between the particle following code ORBIT-RF and the full wave code AORSA, which assumes zero orbit width, shows that finite drift orbit effects are important in modeling high harmonic ICRF beam heating experiments in DIII-D. For a model problem with a neutral beam Maxwellian fast particle distribution, ORBIT-RF qualitatively reproduces the local ICRF wave power damping predicted by AORSA. However, the ORBIT-RF simulation shows a significant quantitative effect from the finite banana orbits of highly energetic beam ions on the edge loss and the RF heating near the magnetic axis that is not reproduced in AORSA. More accurate modeling of the phase information between the electric field amplitudes for the polarizations E_{+} and E_{-} is also required since the E_{-} polarized term becomes comparable to E_{+} in high harmonic ICRF heating simulations. This is being considered under the RF SciDac project.

The last publicly available ASP website for the experimental group has been retired on d3dnff.gat.com. The website has been translated into PHP and placed on diii-d.gat.com. This finalizes the process of synchronizing the user access experience and content maintenance on DIII-D websites. Users will be able to access all DIII-D websites under the same server with a single login as all access control will be done on one machine.

##### November 07, 2008

A MATLAB computer code has been written to calculate the matrix elements of the Fokker Planck operator in the basis functions composed of the products of Legendre polynomials and generalized Laguerre polynomials of arbitrary orders. The algorithm is based on recursive relations among generating functions for these basis functions that have been derived in the past. The code has been used to calculate the neoclassical parallel flows of plasmas with or without impurities, showing that the inclusion of four or five of these basis functions for the first and second order Legendre polynomials yield accuracy better than one part in a thousand. Avoiding the use of model collision operators, the code should be useful for accurately solving the neoclassical transport problem in arbitrary regime of collisionality and general magnetic geometry.

**Disclaimer**

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

*
*