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A. Kirschner, S. Brezinsek, A. Huber, A. Meigs, G. Sergienko, D. Tskhakaya, D. Borodin, M. Groth, S. Jachmich, J. Romazanov, S. Wiesen, C. Linsmeier, JET Contributors:
"Modelling of tungsten erosion and deposition in the divertor of JET-ILW in comparison to experimental findings";
Nuclear Materials and Energy, 18 (2019), 239 - 244.

The erosion, transport and deposition of tungsten in the outer divertor of JET-ILW has been studied for an HMode
discharge with low frequency ELMs. For this specific case with an inter-ELM electron temperature at the
strike point of about 20 eV, tungsten sputtering between ELMs is almost exclusively due to beryllium impurity
and self-sputtering. However, during ELMs tungsten sputtering due to deuterium becomes important and even
dominates. The amount of simulated local deposition of tungsten relative to the amount of sputtered tungsten in
between ELMs is very high and reaches values of 99% for an electron density of 5E13 cm−3 at the strike point
and electron temperatures between 10 and 30 eV. Smaller deposition values are simulated with reduced electron
density. The direction of the B-field significantly influences the local deposition and leads to a reduction if the
E×B drift directs towards the scrape-off-layer. Also, the thermal force can reduce the tungsten deposition,
however, an ion temperature gradient of about 0.1 eV/mm or larger is needed for a significant effect. The
tungsten deposition simulated during ELMs reaches values of about 98% assuming ELM parameters according to
free-streaming model. The measured WI emission profiles in between and within ELMs have been reproduced by
the simulation. The contribution to the overall net tungsten erosion during ELMs is about 5 times larger than the
one in between ELMs for the studied case. However, this is due to the rather low electron temperature in
between ELMs, which leads to deuterium impact energies below the sputtering threshold for tungsten.
1. Introduction
Tungsten (W) is used in present fusion devices and is foreseen for
future ones as plasma-facing material as it has a high melting point and,
compared to other wall material candidates, low sputtering yields and
high threshold energy for sputtering. However, eroded tungsten particles
will not be fully ionised within the core plasma and therefore even
small amounts can lead to plasma dilution and radiation cooling, which
finally can result in the termination of the discharge [1]. Thus, the
processes determining the net erosion source from tungsten wall components
have to be understood adequately to minimise the tungsten
concentration in the core plasma.
As a high-Z material, the deposition of eroded tungsten is expected
to be high [2, 3], which can lead to significantly smaller net erosion
compared to the gross erosion. The measurement of the tungsten.

Erosion & Deposition Tungsten Sputtering Impurity transport JET-ILW

http://dx.doi.org/10.1016/j.nme.2019.01.004