Speaker
David Shaw
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.307.pdf
Low-temperature plasma removal of deposits from fusion first mirrors
D. Shaw1 , A. Gibson1 , M. Kushner2 , E. Wagenaars1
1 York Plasma Institute, York, UK
2 University of Michigan, Ann Arbor, USA
Within a fusion device the optical component closest to the plasma is called the first mirror.
With the device in operation the high energy atoms within the plasma erode the plasma facing
material and redeposit it around the reactor. Mirrors suffer this erosion and re-deposition process
and it causes degradation in the quality of the signal reaching the diagnostics. Erosion is easily
overcome with single crystal or small scale crystal structures but the deposition is substantial
and with no easy solution [1].
The proposed method of removal of these deposits is using a low-temperature plasma in-situ
in order to maintain reflectivity. This involves creating a capacitively coupled plasma using the
mirror itself as the powered electrode. Experiments have been carried out to test this method
and they have yielded good results [2]. Due to the toxicity of the beryllium used in the con-
struction of the first wall the majority of experiments have used aluminium oxide as a proxy.
It is only recently that experiments using beryllium deposits have been conducted, and in lim-
ited numbers. In order to improve the removal process it has become prudent to use computer
simulations. The Hybrid Plasma Equipment Model has been used in order to investigate and
optimise the deposition removal process through simulating conditions and chemistry as close
to the working environment as possible. This has been done in comparison with experimental
results conducted in York and gathered from literature. In order to conduct this work a plasma
chemistry for beryllium has also been created so that both the aluminium oxide experiments
and beryllium experiments can be investigated.
References
[1] A. Costley, T. Sugie, G. Vayakis, et al., Fusion Engineering and Design 74, 74 (2005)
[2] L. Moser, R. Steiner, F Leipold, et al., Journal of Nuclear Materials 463, 463 (2015)
