ABSTRACT
IAEA-F4-TM-42581
IAEA Technical Meeting on Atomic, Molecular and Plasma Material Interaction Data for
Fusion Science and Technology
Determination of absolute erosion yields and S/XB values via Cavity
Ring-Down Spectroscopy in the Pilot-PSI linear device
T. W. Morgana, V. Kvona
a
FOM Institute DIFFER, Nieuwegein, The Netherlands
E-mail address of main author: t.w.morgan@differ.nl
The large heat exhaust expected in DEMO (estimated between 600-1000 MW [1]) produces
extreme challenges for plasma facing components (PFCs) in accommodating and controlling
the resultant high heat fluxes, and motivates investigating innovative materials for the divertor
region. Liquid metals offer several potential advantages over a solid PFC, such as the ability to
replenish the eroded surface, immunity to the effects of neutron embrittlement and the potential
to act as a self-regulating source of radiating impurities to shield the surface from excess heat
loads. As low melting point metals lithium, gallium and tin are the leading candidates but,
especially for the latter two, atomic data is incomplete or non-existent in current databases
orientated around fusion research.
One of the crucial questions in using any PFC is what its erosion flux into the plasma will be.
Generally a standard technique for tokamak research is to determine this spectroscopically
using inverse photon efficiencies (so-called S/XB values [2]) relating photon and particle
fluxes. However, without calculations from collisional radiative models or determination
experimentally of S/XB values this methodology remains unavailable for tin and gallium. At
FOM DIFFER a Cavity Ring Down Spectroscopy (CRDS) system has been installed to
determine absolutely the density of neutrals in the plasma eroded from a liquid tin target. The
system can also be used in principle with other species with ground-excited transitions in the
near UV and visible wavelengths, offering a new methodology for erosion measurements. This
system has been connected to the Pilot-PSI linear device [3] a high flux low temperature linear
plasma device which produces conditions which well replicate those expected in the ITER and
DEMO divertors. In combination with optical emission spectroscopy or filtered camera
observations the CRDS system can be used to determine gross erosion yields and S/XB values
for a variety of plasma densities and temperatures. This can therefore provide valuable
information on surface erosion levels under divertor conditions as well as atomic data useful to
plasma diagnosticians. Initial results from the implementation of the CRDS system in Pilot-PSI
will be presented.
[1] D. Maissonier et al. Nucl Fusion 47 (2007) 1524-1532
[2] A.Pospieszczyk “Diagnostic of edge plasmas by optical method”, in “Atomic and plasmamaterial processes in controlled thermonuclear fusion”, Elsevier, Amsterdam (1993), 213.
[3] van Rooij et al. Appl. Phys. Lett. 90 (2007) 121501
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