Speaker
Damian Bryan King
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1067.pdf
Neutral Beam Injection on JET : Effect on Neutron Discrepancy and Energy
Balance
D.B. King1, C.D. Challis1, E.G. Delabie2, D. Keeling1, G.F. Matthews1, S. Silburn1
and JET contributors*
Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1
Culham Centre for Fusion Energy, UK, 2ORNL, USA,
The dependence of JET neutron discrepancy and energy balance on neutral beam (PINI) selection
has been investigated experimentally.
There has been a consistent discrepancy between neutrons predicted and measured during JET
pulses, with the measured neutrons typically being lower than interpretive simulation results. A
number of investigations into this have been carried out [1] with many explanations excluded.
Further to this the energy balance on JET has shown a discrepancy of ~25% [2]. The neutron
production on JET is split between thermal fusion reactions and beam-target reactions, with
beam-target reactions making the larger contribution in most deuterium-deuterium discharges.
Given this dominance of beam-target reactions and the ubiquity of NBI heating in JET plasmas it
is important to have a good understanding of both the behaviour of JET NBI in the plasma and
the NBI power calibration. To improve this understanding a series of experiments were carried
out involving a single PINI at a time into a stable, L-mode plasma. These pulses were then
analysed using the TRANSP [3] code to determine how the predicted & measured neutrons varied
with PINI selection. To further aid the analysis beam emission spectroscopy was also carried out
and the change in plasma stored energy at beam turn-on was analysed and compared with the
beam power.
The variation of neutron discrepancy with PINI selection will be shown, with some off-axis PINIs
showing a 50% or higher difference in the discrepancy. Other PINI positions showed ~5%
variation in both neutron discrepancy and energy balance. Where possible a comparison between
the same PINI positions on different beamlines will be shown to indicate any separation between
technical and plasma physics causes of a deficit. The details of the method used for NBI power
calibration will also be shown with the systematic errors recalculated to be ~10%. First results of
the stored energy analysis show no disagreement with the beam power calibration within these
errors.
*See the author list of “Overview of the JET results in support to ITER” by X. Litaudon et al. to be published in
Nuclear Fusion Special issue: overview and summary reports from the 26th FEC (Kyoto, Japan, 17-22 Oct 2016)
[1] H. Weisen et al, Nuclear Fusion 57, 7 (2017)
[2] G.F. Matthews et al, Nuclear Materials and Energy 12, 227-233 (2017)
[3] R.J. Goldston et al, J. Comp. Phys 43 (1981) 61
