Wall conditioning throughout the first carbon divertor campaign on Wendelstein 7-X

Wauters, Tom; Brezinsek, Sebastijan; Alonso, Arturo; Brakel, Rudolf; Dinklage, Andreas; Baldzuhn, Juergen; Matveev, Dmitry; Ford, Oliver P.; Vanó, Lilla; Grote, Heinz; Stange, Torsten; Laqua, Heinrich; Goriaev, Andrei; Fellinger, Joris; König, Ralf

doi:10.1016/j.nme.2018.11.004

Journal Article

FZJ-2018-07202

Wall conditioning throughout the first carbon divertor campaign on Wendelstein 7-X

Wauters, T. (Corresponding author)FZJ* ; Goriaev, A.FZJ* ; Alonso, A. ; Baldzuhn, J. ; Brakel, R. ; Brezinsek, S.FZJ* ; Dinklage, A. ; Grote, H. ; Fellinger, J. ; Ford, O. P. ; König, R.FZJ* ; Laqua, H. ; Matveev, D.FZJ* ; Stange, T. ; Vanó, L.

2018
Elsevier Amsterdam [u.a.]

Nuclear materials and energy 17, 235 - 241 (2018) [10.1016/j.nme.2018.11.004]

This record in other databases:

Please use a persistent id in citations: http://hdl.handle.net/2128/20364 doi:10.1016/j.nme.2018.11.004

Abstract: Controlling the recycling of hydrogen and the release of impurities from the plasma facing components proved to be essential and challenging throughout the first divertor campaign on W7-X. This paper discusses the conditioning requirements throughout the first divertor campaign on Wendelstein 7-X. Baking at 150°C and glow discharge conditioning (GDC) in H2 is performed after the initial pump down of the vacuum vessel. Experimental programs in hydrogen are interlaced with He discharges to desaturate the wall from hydrogen, recover good recycling conditions and hence establish plasma density control. Optimized He ECRH wall conditioning procedures consisted of sequences of short discharges with fixed duty cycle. He-GDC remained however needed before each experimental day to fully offset the hydrogen inventory build-up. A significant increase in the divertor temperature is observed throughout an operational day, enhancing outgassing of CO and H2O. Preliminary recombination-diffusion modelling of hydrogen outgassing suggests enhanced diffusion to deeper surface layers with increasing wall temperature, which results in better wall pumping. This indicates that the experienced plasma performance degradation throughout an operational day results from increased impurity outgassing at higher wall temperature rather than hydrogen saturation of the wall.

Classification: