DIII-D Research in Support of ITER
E.J. Strait, (E. Schuster), et al. (Collaboration Paper)
IAEA Fusion Energy Conference
Geneva, Switzerland, 13-18 October 2008
Abstract
|
|
DIII-D research is providing key information for the design and
operation of ITER. Discharges that simulate ITER operating scenarios
in conventional H-mode, advanced inductive, hybrid, and steady state
regimes have achieved normalized performance consistent with ITER’s
goals for fusion performance. Stationary discharges with high beta_N
and 90% noninductive current that project to Q=5 in ITER have been
sustained for a current relaxation time (~2.5 s), and high-beta
wall-stabilized discharges with fully non-inductive current drive have
been sustained for more than one second. Detailed issues of plasma
control have been addressed, including the development of a new
large-bore startup scenario for ITER. A broad research program
provides the physics basis for predicting the performance of ITER.
Recent key results include the discovery that the L-H power threshold
is reduced with low neutral beam torque, and the development of a
successful model for prediction of the H-mode pedestal height in DIII-D.
Research areas with the potential to improve ITER’s performance include
the demonstration of ELM-free "QH-mode" discharges with both co and
counter-injection, and validation of the predicted torque generated by
static, non-axisymmetric magnetic fields. New diagnostics provide
detailed benchmarking of turbulent transport codes and direct
measurements of the anomalous transport of fast ions by Alfvén
instabilities. DIII-D research also contributes to the basis for
reliable operation in ITER, through active control of the chief
performance-limiting instabilities. Recently, ELM suppression with
resonant magnetic perturbations has been demonstrated at collisionality
similar to ITER’s, while simultaneous stabilization of NTMs (by
localized current drive) and RWMs (by magnetic feedback) has allowed
stable operation at high beta and low rotation. In research aimed at
improving the lifetime of material surfaces near the plasma, recent
experiments have investigated several approaches to mitigation of
disruptions, including injection of low-Z gas and low-Z pellets, and
have shown the conditions that minimize core impurity accumulation
during radiative divertor operation. Investigation of carbon erosion,
transport, and co-deposition with hydrogenic species, and methods for
the removal of co-deposits, will contribute to the physics basis for
initial operation of ITER with a carbon divertor.