Speaker
Kieran Joseph McCarthy
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.112.pdf
Pellet Injection in the Stellarator TJ-II
K. J. McCarthy1, N. Panadero1, S. K. Combs2, N. Tamura3, J. L. Velasco1, E. Ascasíbar1, J.
Baldzuhn4, E. de la Cal1, T. Estrada1, J.M. Fontdecaba1, R. García1, J. Hernández1, F. Koechl5,
M. Liners1, A. López-Fraguas1, A. V. Melnikov6, M. Navarro1, D. Silvagni7, J. L. de Pablos1,
I. Pastor1, A. Soleto1, A. Zhezhera8, TJ-II team1, LHD experimental group3, and W7-X team4
1
Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain
2
Fusion & Materials for Nuclear Systems Division, ORNL, Tennessee, USA
3
National Institute for Fusion Science, Toki, Japan
4
Max-Planck-Institut für Plasmaphysik, Greifswald, Germany
5
Atominstitut, Technische Universität Wien, Vienna, Austria
6
National Research Centre ‘Kurchatov Institute’, Moscow, Russia
7
Max-Planck-Institut für Plasmaphysik, Garching, Germany
8
Institute of Plasma Physics, NSC KIPT, Kharkov, Ukraine
Cryogenic pellet injection (PI) is a standard tool on most medium- and large-sized
magnetically confined plasma devices. Technologies are well developed and PI systems are
earmarked as critical items in future reactors. Despite significant progress, a complete
comprehension of ablation, enhanced ablation, and particle drift/diffusion remains to be
achieved. Indeed, understanding these is essential to improve codes and to optimize fuelling.
In contrast, in some devices, other pellet types are also often injected, e.g. impurities. Given
the similar ablation physics, etc., comparative studies may help extend current knowledge.
A cryogenic PI system is used for low-field side injections into the TJ-II, a highly flexible,
medium-sized, stellarator. TJ-II is fitted with a wide range of diagnostics, making it a
powerful tool for pellet physics studies [1, 2]. Good agreement is found between experimental
and predicted profiles (ablation/deposition) when using a new stellarator version of the HPI2
code [3]. For instance, fast-frame imaging of the ablation process finds outward plasmoid
drifts that concur with simulations. This has permitted benchmarking HPI2 for W7-X and has
provided input for related studies [3]. Moreover, comparative studies, using a TESPEL (C8H8)
system piggybacked to the up-stream end of the TJ-II PI, substantiate the influence of pellet
particle mass on plasmoid drift, deposition profile peaking and deposition efficiency [4].
Finally, TJ-II studies reveal a strong penetration depth/fuelling efficiency relationship, and
show that Er changes are consistent with effective ion charge variations and that density
fluctuations are strongly reduced over a short time scale immediately after an injection.
[1] J. L. Velasco et al., Plasma Phys. Control. Fusion 58 (2016) 084004.
[2] K. J. McCarthy et al., Nucl. Fusion 57 (2017) 056039.
[3] N. Panadero et al., Nucl. Fusion 58 (2017) 026025.
[4] K. J. McCarthy et al., Europhys. Lett. 120 (2017) 25001.
