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(CD2/EX9/3) Progress Towards Sustainment of Advanced Tokamak Modes in DIII-D

   
B. W. Rice , B. W. Stallard 
Lawrence Livermore National Laboratory, Livermore, California, U.S.A.
 
K. H. Burrell , J. R. Ferron , C. M. Greenfield , G. L. Jackson , L. L. Lao , R. J. La Haye , T. C. Luce , E. J. Strait , T. S. Taylor , A. D. Turnbull 
General Atomics, P.O. Box 85608, San Diego, California 92186-9784, U.S.A.
 
E. J. Synakowski 
Princeton Plasma Physics Laboratory, Princeton, New Jersey, U.S.A.
 
M. R. Wade 
Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.

Abstract
Improving confinement and beta limits simultaneously in long-pulse ELMy H-mode  discharges is investigated. The product $\rm\beta_NH_{98y}$ serves as a useful figure-of-merit for performance, where $\rm\beta_N \equiv \beta/(I/aB)$ and $\rm H_{98y}$ is the ratio of the thermal confinement time relative to the most recent ELMy H-mode confinement scaling established by the ITER confinement database working group. In discharges with $\rm q_{\mbox{min}} > 1.5$ and negative central magnetic shear , $\rm\beta_NH_{98y} \sim 4$ is sustained for $\sim$ 1 s. Although peaked profiles are observed, strong internal transport barriers are not present. Further increases in $\rm\beta_N$ in these discharges is limited by neoclassical tearing modes (NTM) in the positive shear region. In another recently developed regime, $\rm\beta_NH_{98y} > 6$ has been sustained during large infrequent ELMs in non-sawtoothing discharges with $\rm q_0 \sim 1$. This level of performance is similar to that obtained in ELM-free regimes  such as VH-mode . The limitation on $\rm\beta_N$ and pulse length in these discharges is also the onset of NTMs.

   

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