Speaker
Cecilia Bruhn
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1089.pdf
Core boron transport studies using CXRS at ASDEX Upgrade
C. Bruhn1,2 , R.M. McDermott1 , C. Angioni1 ,
J. Ameres3,1 ,V. Bobkov1 , M. Cavedon1 , R. Dux1 , A. Kappatou1 ,
A. Lebschy1,2 , R. Ochoukov1 , P. Manas1 , and the ASDEX Upgrade Team
1 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany
2 Physik-Department E28, Technische Universität München, D-85748 Garching, Germany
3 Zentrum Mathematik M16, Technische Universität München, Garching, Germany
Impurities in fusion plasmas arise from many different sources including the erosion and
sputtering of material from plasma facing components, the intentional injection of impurities
for divertor cooling and core radiation control, and the production of helium from the fusion
process itself. To achieve optimum fusion performance, future fusion reactors need to control
the build up of both high- and low-Z impurities in the plasma core. Therefore, it is important
to develop and validate our theoretical understanding of impurity transport in fusion plasmas.
At ASDEX Upgrade (AUG), a novel method of studying the core boron transport has been de-
veloped and is being used to validate the theoretical understanding as well as the mechanisms
behind low-Z impurity transport. This method utilizes the fact that a modulation of the power
from the ion cyclotron resonance frequency (ICRF) antennae induces a modulation of the boron
density, which can be measured with high spatial and temporal resolution by the charge ex-
change recombination spectroscopy (CXRS) diagnostics. From a time perturbed boron density
signal the transport coefficients, D and v, can be separately determined with high radial reso-
lution by solving an inverse problem, and this is in contrast to what is usually being done for
low-Z impurities. This method, thus, combines the advantages of a transient transport analysis
performed on modulated signals over many periods, as often applied for heat transport stud-
ies, with the high radial resolution enabled by the CXRS diagnostic. It has been applied to a
wide variety of AUG H-mode plasmas, and from this, a database of core boron transport coeffi-
cients has been assembled. This database and how the transport coefficients depend on the local
plasma parameters will be presented in this contribution as well as an in-depth comparison to
theory. For the bulk of the database, there is a strong scaling of the transport coefficients with
the electron cyclotron resonance heating (ECRH) power and consequently with Te /Ti . Addi-
tionally, there is a quantitative agreement between the measured and the predicted theoretical
diffusion coefficients. However, in all cases the convection is predicted to be more inward than
is measured, resulting in an over-prediction of the peaking of the impurity density profiles.
These results and explanations to the discrepancy will be presented in this contribution.
