Speaker
Jannis Oelmann
(Forschungszentrum Jülich GmbH)
Description
Monitoring of material deposition on and fuel retention in the first wall plasma-facing components is a key diagnostic issue for the next step fusion devices in view of lifetime estimates and operational safety. Lifetime is determined by first wall erosion and in metallic components by the helium content (fusion ash), whereas operational safety is determined by tritium (fusion fuel) retention and dust production from thick layers. Laser-based diagnostics are suitable as in-situ as well as ex-situ diagnostics to access the critical quantities, and indeed, Laser-Induced Desorption (LID) is foreseen to measure in-situ the tritium content in ITER and monitor the inventory with respect to the safety limit and potential cleaning measures.
Whereas with a microsecond laser a significant fraction of fuel in the first wall might not be released with LID [1], we present a setup for depth-resolved post mortem and possible in-situ analysis of hydrogen content combing picosecond laser ablation with quadrupole mass spectroscopy. Using a 35 ps laser pulse duration and a wavelength of $\lambda$ = 355 nm (Nd:VO$_4$ 3rd harmonic), the thermal penetration depth is in the same order of magnitude as the optical penetration depth (𝒪(100 nm)) and avoids any matrix and smearing effects, but provides complete fuel release within the laser spot. The ablation rate of the laser pulse is $\Delta h \approx$ (50 – 200) nm, allowing also to measure several µm thick deposition layers. The residual gas analysis enables in addition a clear separation of hydrogen isotopes including tritium and deuterium in fusion devices. A comparison of the complex material deposition and retention in graphite tiles installed in the stellarator W7-X in the first experimental campaign by Laser-Induced Breakdown Spectroscopy (LIBS) and Short Pulse Laser Ablation Gas analysis (SPLAG) will be presented. The quantitative information acquired by these techniques will be discussed in order to demonstrate the capabilities of these methods. Additionally, hydrogen retention analysis by Laser-Induced Ablation Spectroscopy (LIAS) measurements is presented and compared to LIBS using graphite samples from the EAST tokamak.
[1]: G. De Temmerman et al., Nuclear Materials and Energy (2016),\\http://dx.doi.org/10.1016/j.nme.2016.10.016
*Corresponding author: tel.: +49 2461 613119, e-mail: *j.oelmann@fz-juelich.de*
Primary author
Jannis Oelmann
(Forschungszentrum Jülich GmbH)
Co-authors
C. Li
(Forschungszentrum Jülich GmbH)
C. P. Dhard
(Max-Planck-Institut für Plasmaphysik)
Ch. Linsmeier
(Forschungszentrum Jülich GmbH)
F Ding
(Institute of Plasma Physics, Chinese Academy of Sciences, Hefei)
G.-N. Luo
(Institute of Plasma Physics, Chinese Academy of Sciences, Hefei)
H Ding
(School of Physics and Optical Engineering, Dalian)
N. Gierse
(Forschungszentrum Jülich GmbH)
R. König
(Max-Planck-Institut für Plasmaphysik)
S. Brezinsek
(Forschungszentrum Jülich GmbH)
Z. Hu
(Institute of Plasma Physics, Chinese Academy of Sciences, Hefei)
