Speaker
Benedikt Geiger
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1081.pdf
Fast-ion transport in advanced tokamak scenarios with qmin close to two
at ASDEX Upgrade
B. Geiger1 , R. Akers2 , A. Bock1 , M. Dunne1 , L. Giannone1, J. Hobirk1 ,
A.S. Jacobsen1 , P. Lauber1 , P. Zs. Pölöskei1 , M. Salewski3, P. A. Schneider1 ,
A. Snicker4 , A.J. van Vuuren1 , M. Willensdorfer1 and the ASDEX Upgrade Team
1 MPI für Plasmaphysik, D-85748 Garching, Germany
2 CCFE, Culham Science Centre, Abingdon, Oxon, United Kindom
3 PPFE, Department of Physics, DTU, DK-2800 Kgs. Lyngby, Denmark
4 Department of Applied Physics, Aalto University, FI-00076 AALTO, Finland
Steady state operation of tokamaks is demanding since the toroidal plasma current needs to
be sustained by non-inductive means [1]. Although external current drive sources are available,
their extensive use would yield an unacceptably high recirculated power fraction in future fu-
sion power plants. Thus, advanced tokamak scenarios are needed that feature high fractions
of the intrinsic bootstrap current. The latter can be maximized in discharges with off-axis cur-
rent distributions (low central poloidal fields) and internal transport barriers (strong gradients).
Such discharge conditions are, however, difficult to maintain since they are prone to impurity
accumulation [2] and ideal modes [3].
Recently, a stable advanced scenario with a current hole [4] in the plasma center and inter-
nal transport barriers in the electron and ion temperature channels was maintained for several
confinement times in ASDEX Upgrade. The discharges are almost non-inductive even though
counter electron cyclotron current drive (ECCD) was used for current-profile tailoring in the
plasma center. However, the high plasma pressure and the exotic safety factor profile (qmin
close to two) yield a variety of magneto-hydrodynamic modes that might reduce the confine-
ment of suprathermal particles. The corresponding fast-particle transport will be discussed to-
gether with the analysis of the stability and performance of the new discharge scenario. This
involves detailed diagnostic measurements and their interpretation, as well as modelling results
of the thermal and fast-ion transport.
References
[1] WENNINGER, R. et al., Nuclear Fusion 57 (2017) 016011.
[2] DUX, R. et al., Nuclear Fusion 44 (2004) 260.
[3] WESSON, J. et al., Nuclear Fusion 25 (1985) 85.
[4] FUJITA, T. et al., Nuclear Fusion 43 (2003) 1527.
