### Theory Weekly Highlights for May 2001

##### May 18, 2001

At the recent international RF conference at Oxnard, CA., results of our Orbit-RF simulation were in agreement with the averaged-orbit simulation of the Swedish group (Hellsten, et. al.) that finite drift orbit effect is responsible for the co-rotation in the ICRH simulation. Both calculations showed that with finite Doppler shift, the rotation can peaked off-axis which was shown in the preliminary result reported by JET.

##### May 11, 2001

The first simulations of the H-mode pedestal with the GLF23 driftwave based transport model were performed. It was found that the predicted pedestal temperature was higher than that measured in DIII-D H-mode discharges, but that the width was predicted reasonably well. In related work, stability analysis of intermediate n peeling-ballooning modes in a set of equilibria with limited second stability access found that peeling mode stability determined the height but not the width of the edge pedestal. These preliminary results suggest that transport due to driftwaves limits the pedestal width, whereas edge localized MHD modes limit the pedestal height. Work is underway to determine how generally this result applies. This initial analysis also revealed the need to improve the treatment of the magnetic geometry in GLF23 in order to be able to model the plasma edge more realistically.

##### May 04, 2001

The orbits of particles in the core region of a rotating tokamak plasma are analyzed. It is found that the phase space topologies of finite orbits differs significantly from those of thin orbit considerations. Both the fast ion and low energy ion trapped-passing boundaries are strongly modified. The finite orbit analysis also leads to improved analytic formulae for orbit averaged quantities useful for transport and fast ion instabilities applications.

**Disclaimer**

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