Speaker
C. Desgranges
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1018.pdf
VUV spectroscopy measurements on WEST first plasmas
C. Desgranges1, R. Guirlet1 ,O. Meyer1, J.L. Schwob2, S. Vartanian1 and the WEST team
1
CEA, IRFM, 13108 St-Paul-Lez-Durance, France
2
Racah Institute of Physics, The Hebrew University, 91904 Jerusalem, Israel
The WEST machine aims at testing actively cooled full W monoblock Plasma Facing
Units under long plasma discharge, with thermal loads of the same magnitude as those
expected for ITER. For the first operation phase, copper plasma facing components were
directly tungsten coated and carbonaceous components were coated with a molybdenum
sublayer covered by a tungsten layer. Ten seconds stable L-mode X-point plasma discharges
were routinely performed, including up to 2.5 MW LHCD. During the first plasmas, some
runaway electron control issues were the cause of plasma contamination by wall material. The
VUV spectroscopy measurements characterising this contamination are reported in this paper.
WEST as well as Tore Supra, is equipped with two VUV spectrometers providing
plasma impurity measurements. To perform tungsten spectroscopy measurements, various
spectral ranges were selected. The spectral feature around 5 nm wavelength has been
observed and allowed to show that the tungsten content increased on a pulse-to-pulse basis
correlated with the LHCD power ramp-up. It showed also that in the same phase of the
campaign, the core electron temperature was increased from 300 eV to more than 2 keV (as
confirmed by the ECE electron temperature measurements). Operational limitations due to the
tungsten content increase were also observed in some occasions and induced a modification of
the plasma control strategy. Higher tungsten ionization stages (W38+-W45+) have been
observed in the 11.5-15.5 nm wavelength range consistently with AUG observations [1]
In the same time, in view of a more effective impurity monitoring, a thorough line
identification of the VUV spectra has been performed: Copper and Molybdenum line
brightnesses have been identified and studied by comparing them with the sources deduced
from the visible spectroscopy diagnostics. Copper is correlated with the LH power while
Molybdenum is due to runaway electron damages on tungsten coated plasma facing
components. The latter cause might explain also why carbon, which was completely absent
from the spectra at the beginning, appeared later in the campaign.
[1] T. Pütterich et al. 2008 Plasma Phys. Control. Fusion 50 085016
