Publications in Scientific Journals:

A.C.C. Sips, M. Proschek et al.:
"Steady state advanced scenarios at ASDEX Upgrade";
Plasma Phys. Control. Fusion, 44 (2002), B69 - B83.

English abstract:
Recent experiments at ASDEX Upgrade have achieved advanced scenarios
with high betaN (>3) and confinement enhancement over ITER98(y, 2)
scaling, HH98y2 = 1.1-1.5, in steady state. These discharges have been
obtained in a modified divertor configuration for ASDEX Upgrade,
allowing operation at higher triangularity, and with a changed neutral
beam injection (NBI) system, for a more tangential, off-axis beam
deposition. The figure of merit, betaN*HITER89-P, reaches up to 7.5 for
several seconds in plasmas approaching stationary conditions. These
advanced tokamak discharges have low magnetic shear in the centre, with
q on-axis near 1, and edge safety factor, q95 in the range 3.3-4.5. This
q-profile is sustained by the bootstrap current, NBI-driven current and
fishbone activity in the core. The off-axis heating leads to a strong
peaking of the density profile and impurity accumulation in the core.
This can be avoided by adding some central heating from ion cyclotron
resonance heating or electron cyclotron resonance heating, since the
temperature profiles are stiff in this advanced scenario (no internal
transport barrier). Using a combination of NBI and gas fuelling line,
average densities up to 80 90% of the Greenwald density are achieved,
maintaining good confinement. The best integrated results in terms of
confinement, stability and ability to operate at high density are
obtained in highly shaped configurations, near double null, with delta =
0.43. At the highest densities, a strong reduction of the edge localized
mode activity similar to type II activity is observed, providing a
steady power load on the divertor, in the range of 6MWm-2, despite the
high input power used (>10 MW).

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