Speaker
W. Zhang
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.102.pdf
Plasma edge modelling with ICRF coupling
W. Zhang , D. Aguiam3, R. Bilato1, V. Bobkov1, D. Coster1, Y. Feng4, P. Jacquet5, T. Lunt1,
1,2
J.-M. Noterdaeme1,2, W. Tierens1, the ASDEX Upgrade team1, the EUROfusion MST1
Team6
1
Max-Planck-Institut für Plasmaphysik, Garching, Germany
2
Applied Physics Department, University of Ghent, Ghent, Belgium
3
Instituto de Plasmas e Fusão Nuclear, IST, Universidade de Lisboa, Lisboa, Portugal
4
Max-Planck-Institut für Plasmaphysik, Greifswald, Germany
5
CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
6
see http://www.euro-fusionscipub.org/mst1
wei.zhang@ipp.mpg.de
This contribution mainly addresses two important issues of plasma heating with waves in
the Ion Cyclotron Range of Frequencies (ICRF): i) improving the ICRF power coupling; ii)
understanding the ICRF – edge plasma interactions.
The coupling of ICRF power to the plasmas depends sensitively on the scrape-off layer
(SOL) density in front of the antennas because the fast wave is evanescent below the cut-off
density. Previous experiments on ASDEX Upgrade and JET indicate that by shifting the
fuelling gas source from the divertor to the main chamber, the density in front of the antennas
and thus the ICRF coupling can be greatly increased. To understand this, the 3D edge plasma
fluid and neutral particle transport code EMC3-EIRENE was used to calculate 3D SOL
density, and the FELICE and RAPLICASOL codes were used to calculate the antenna
coupling resistances. Good qualitative agreements are found between simulations and
experiments. They indicate that midplane gas puffing close to the antennas increases the
ICRF coupling most significantly (by ~120%) and top gas puffing increases the coupling
only to a moderate level (by 20%-40%). Calculations for ITER also show that midplane gas
valves close to the antennas are most effective in increasing ICRF coupling in ITER.
There is a mutual influence between ICRF waves and plasma density at the edge, and in
particular the measured density convection at the plasma edge is likely influenced by ICRF
waves. This density convection is simulated with EMC3-EIRENE code by supplying the
sheath potential as input in two different modalities: i) measured (forced problem); ii)
calculated by running in an iterative loop - RAPLICASOL code for E||, SSWICH code for the
sheath potential, and EMC3-EIRENE itself for the plasma density (consistency loop). The
calculated density convection is in qualitative agreement with the measurements from
reflectometers embedded in the antenna or reciprocating probe. The results indicate that large
convective cells develop in the top and bottom of the antennas when operated with
unfavorable phasing and power ratio between the straps. In comparison to the conventional
2-strap antenna, the novel 3-strap antennas installed in ASDEX Upgrade decrease the sheath
potential and the associated E×B convection when operated with the proper phasing and
power ratio.
