Speaker
Massimo Nocente
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.103.pdf
A quantitative comparison between confined fast ion data and models from
radio frequency heating experiments with the three ion scenarios at JET
M. Nocente1, Ye. O. Kazakov2, V.G. Kiptily3, T. Craciunescu4, J. Eriksson5, L. Giacomelli1,
G. Gorini1, C. Hellesen5, E. Lerche2, M. Mantsinen6, J. Ongena2, S. Sharapov3,
M. Tardocchi1, D. Van Eester2 and JET Contributors*
1
Dipartimento di Fisica and Istituto di Fisica del Plasma, Milano, Italy
2
Laboratory for Plasma Physics, LPP-ERM/KMS, TEC Partner, Brussels, Belgium
3
Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, UK
4
National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania
5
Department of Physics, Uppsala University, Uppsala, Sweden
6
Barcelona Super Computing Centre and ICREA, Barcelona, Spain
*See the author list of X. Litaudon et al 2017 Nucl. Fusion 57 102001
Electronic mail: massimo.nocente@mib.infn.it
Ion cyclotron resonance heating (ICRH) by radio frequency waves is a commonly adopted tool to
tailor the plasma discharge and boost the fusion performance. A recent breakthrough in this field has
been the theoretical discovery [1] and subsequent experimental demonstration [2] that radio frequency
power can be more efficiently absorbed by exploiting the favorable polarization properties of the
wave electric field in vicinity of the left handed cut-off layer compared to conventional minority
heating. This is possible in the so called 3 ion scenarios, where the plasma mixture is carefully
adjusted so that two majority species, say hydrogen and deuterium, define the propagation properties
of the wave, while a third species, at typical concentrations of few percents or less, absorbs the power
with virtually 100% efficiency.
Experiments at JET on the 3 ion scenarios have so far focused on D and 3He acceleration and have
provided unambiguous qualitative evidence of the acceleration of fast ions to the MeV range. This
ranges from the excitation of Alfvén eigenmodes to the observation of a rich gamma-ray emission
from a variety of nuclear reactions between MeV range fast ions and 9Be impurities in the plasma (see
figure 1).
In this work, we present a quantitative study of confined fast ion data from 3 ion scenario
experiments at JET and a comparison with predictions from advanced radio frequency codes that
solve the wave propagation in the plasma and calculate the distribution function of the fast ions by
means of a Monte Carlo kick operator. Synthetic diagnostics are used as means to bridge the gap
between simulations of the fast ion phase space and indirect experimental data on the nuclear
emission spectra from 3 ion plasmas. Although the enhancement of ICRH in the 3 ion scheme
compared to minority heating is unambiguous, we find that data suggest mean fast ion energies which
are significantly lower than predictions. Possible additional physics effects that might be needed to
reconcile simulations and the experimental findings, such as the role of Alfven eigenmodes in
effectively ejecting the most energetic ions or the super-adiabaticity of the fast ions as they get
progressively accelerated by the wave electric field, are discussed.
Figure 1. Gamma-ray spectrum from reactions
between fast 3He ions and 9Be impurities in 3 ion
ICRH experiments at JET. A detailed analysis of the
complex gamma-ray spectrum born in these reactions
resolves the individual contributions to the emission,
which are used to determine the 3He ion energies for
comparison with models.
[1] Ye.O. Kazakov et al., Nucl. Fusion 55, 032001 (2015)
[2] Ye.O. Kazakov et al., Nature Physics 13, 973 (2017)
