Speaker
Michael Fitzgerald
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.102.pdf
Losses of fusion products due to fishbones on JET and predictions for
burning plasmas.
M. Fitzgerald, J. Buchanan, S. E. Sharapov, V. G. Kiptily, M. Sertoli, G. Szepesi, J. Boom,
R. Akers, D. King, and JET contributors*
EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
Fishbones are ubiquitous in high performance JET plasma and are typically considered
benign. However, in recent high-performance hybrid experiments, sporadic and explosive
fishbones have been observed which correlate with decreases in performance and main
chamber hotspots. Additionally, recent unambiguous measurements obtained with a 2D
scintillator probe and fast acquisition show coherent losses of fusion product protons and
tritons due to these explosive fishbones
[1]. This is particularly of note due to the
velocities of fusion products being much
too large to resonate with the fishbone.
Using careful MHD marker constrained
EFIT reconstructions, we can show that
the orbits of the lost fast fusion products
are due to barely trapped/confined
Figure 1: HALO predictions of TRANSP fusion product
particles being ejected by the mode. Modelling numbers in equilibrium (left) and with the fishbone
(right). Calculated losses are completely due to FLR
the fishbone as a conventional n=1 MHD effects.
internal kink oscillation we use HAGIS and the newly developed HALO (HAgis LOcust)
code to confirm the non-resonant losses of fusion products. In the HAGIS drift calculations,
the energy content of those losses is insufficient to explain the observed hotspots, however
full-orbit HALO calculations show that a combination of magnetic-moment scattering, and
wall proximity cause fishbones to produce a 25% loss of D-D fusion products at the
experimentally observed location of the hotspot (Figure 1). A breakdown in magnetic moment
conservation leads to a rapid diffusion in pitch-angle space.
Extrapolations to JET DT and ITER will be presented that show the implications for alpha
particle losses due to this previously neglected FLR mechanism for fishbone induced
losses. Losses of this type on ITER are expected to be substantially less than 1%
[1] V. G. Kiptily et al. Nucl. Fusion, vol. 58, no. 1, p. 14003, Jan. 2018.
*
See the author list of “X. Litaudon et al. 2017 Nucl. Fusion 57 102001”
