7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

First-time demonstration of the three-ion scheme for radio-frequency heating indeuterium-tritium plasmas at the Joint European Torus
M. Nocente1,2, Y. Kazakov3, J. Garcia4, V. Kiptily5, J. Ongena3 Z. Stancar5, K. Crombe3, A. DalMolin2, E. De La Luna6, J. Eriksson7, Z. Ghani5, G. Gorini1, C.F. Maggi5, P. Mantica2, G. Marcer1,M. Maslov5, O. Putignano2, D. Rigamonti2, M. Salewski8, S. Sharapov5, P. Siren5, M. Tardocchi2
and JET Contributors91
Department of physics, University of Milano-Bicocca, Italy
2Institute for Plasma Science and Technology, National Research Council, Italy
3
Laboratory for Plasma Physics, LPP ERM/KMS, Belgium
4CEA, IRFM, France
5
United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, United Kingdom
6
Laboratorio Nacional de Fusion CIEMAT, Spain
7Uppsala University, Sweden
8
Technical University of Denmark, Denmark
9
See the author list of J. Mailloux et al 2022 Nucl. Fusion 62 042026
e-mail (speaker): massimo.nocente@unimib.itThe three-ion schemes have recently emerged as aneffective method for plasma heating by radiofrequency(RF) waves in plasmas predominantly made by deuterium
or hydrogen [1]. The schemes rely on the acceleration ofa minority absorber (with a typical concentration of lessthan 1%) when the main plasma is made by two majority
species, for example D-3He or H-D, and that determine thewave polarization.
An important application of the schemes, as predicted bytheory, is the capability to efficiently accelerate heavy
impurity ions, such as 9Be in a machine with a beryllium
wall, and in reactor relevant deuterium-tritium plasmas.
Due to their large critical energy, the fast impurity ions arethen expected to transfer their energy predominantly tobulk ions by Coulomb collisions, resulting in an increaseof the ion temperature and, hence, in an enhanced fusion
rate by thermonuclear reactions.
In this talk, we present the first-time demonstration ofheavy impurity heating with the three-ion scheme indeuterium-tritium plasmas of the Deuterium Tritium 2
experimental campaign (DTE2) of the Joint European
Torus (JET). The experiments were conducted in 2021 andconsisted in 5 successful pulses in plasmas of deuteriumwith a concentration of tritium in the range 50% to 75%,
at a core magnetic field BT=3.7 T and plasma currents
between 2 MA and 2.5 MA. Neutral Beam Injection (NBI)
at a moderate power in the range 2 MW to 8 MW was used
to sustain the plasmas and was complemented with ion
cyclotron resonance heating (ICRH) at power levels ofabout 2 MW with core deposition on 9Be impurities.
Evidence of the successful energy transfer from the fastheavy impurities to bulk plasma ions was shown by
several signals. The plasma stored energy was found toincrease by about 0.28 MJ/MW when ICRH was applied,
as compared to 0.20 MJ/MW in NBI only phase. This wasaccompanied by a steepening of the ion temperature (T i)
profile as measured by charge exchange recombination
spectroscopy (CXRS) and which extrapolates to anincrease of the core ion temperature from 4 keV to 5 keV
for phases with NBI only and with combined NBI andICRH, respectively. Further evidence of increased thermal
ion heating induced by ICRH was provided by neutron
diagnostics. A ≈40% increase of the global neutronemission in the ICRH phase was observed together with apeaking of the neutron profile in the core, as determinedby the neutron cameras. Novel synthetic diamonddetectors [2] were used to measure the thermal and beamtarget contributions to the neutron emission and showed
an increase of the former component in the ICRH phase,in agreement with the enhancement of Ti. As counterproofof 9Be acceleration, we have performed discharges wherethe D:T ratio was varied from 50:50 to 75:25 which,according to theory, makes the RF power absorbed
predominantly by the tritium beam in lieu of 9Be. This wasexperimentally demonstrated by the observed variationsof the thermal and beam-target contributions to theneutron spectrum measured by diamond detectors. As asecond goal of the experiment, we were also able todemonstrate measurements of the fusion power by meansof the detection of the spectrum of 17 MeV gamma-rays
produced by d+t→5He+ reactions, which has an interestin view of developing an alternative method to neutron
diagnostics for the determination of the fusion power in areactor.
The implications of these results for bulk ion heating of
deuterium-tritium plasmas of next step tokamaks will
finally be discussed, especially with reference to the useof extrinsic impurities in lieu of 9Be as the ICRH absorberin machines that do not have beryllium as their first wallmaterial.
References[1] Y. Kazakov et al. Physics of Plasmas 28 020501(2021)[2] M. Nocente et al. Rev. Sci. Instrum. 93 093520(2022)