2:00 PM–5:00 PM, Monday, November 17, 2008
- Landmark A
Chair: Piero Martin, Consorzio RFX - Associazione EURATOM-ENEA sulla fusione, Padova (Italy)
Abstract ID: BAPS.2008.DPP.CI1.3
3:00 PM–3:30 PM
C.T. Holcomb
(Lawrence Livermore National Laboratory)
Recent studies on DIII-D have elucidated key aspects of the dependence of stability, confinement, and density control on the plasma magnetic configuration, leading to noninductive operation (i.e., total inductive flux change $\approx\,$0) for $>$1$\,$s with pressure 30\% above the free boundary limit. Achieving fully noninductive operation requires high $\beta$, good confinement, and density control through divertor operation. Plasma geometry affects all of these. Ideal MHD modeling of the $n=1,2,$ and 3 external kink stability suggests it may be optimized by adjusting the shape parameter known as squareness ($\zeta$). Experiments confirm stability varies strongly with $\zeta$ in qualitative agreement with the modeling. Optimization of $n=1$ stability also seems to raise pedestal stability. Adjusting $\zeta$ above and below the midplane independently allows for small changes in the magnetic divertor balance about a double-null (DN) configuration. Energy confinement is found to be sensitive to this balance, with 20\% higher confinement observed in a balanced DN compared to a slightly unbalanced case. However, adequate density control requires a small imbalance to achieve densities necessary for efficient external noninductive current drive. The best density control (20\%-30\% below the balanced DN case) is obtained with a slight imbalance toward the divertor opposite the ion grad(B) drift direction. Consistency of modeling with these observed effects requires inclusion of $E\times B$ drifts in the divertor. Simultaneous optimization has been applied to achieve noninductive current fractions near 1 for over 1$\,$s with $\beta_N \sim\,$3.5-3.7, bootstrap fraction $>$65\%, and good confinement.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.DPP.CI1.3