Speaker
Yevgen Kazakov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1047.pdf
Application of three-ion species ICRH scenarios for ITER operation
Ye.O. Kazakov1, M. Schneider2, J. Ongena1, R. Bilato3, J.M. Faustin4, E. Lerche1,
D. Van Eester1 and J.C. Wright5
1
Laboratory for Plasma Physics, LPP-ERM/KMS, Brussels, Belgium
2
ITER Organization, Route de Vinon-sur-Verdon, St. Paul-lez-Durance Cedex, France
3
Max-Planck-Institut für Plasmaphysik, Garching, Germany
4
Max-Planck-Institut für Plasmaphysik, Greifswald, Germany
5
Plasma Science and Fusion Center, MIT, Cambridge, USA
E-mail: kazakov@chalmers.se
The application of heating and current drive scenarios, including ion cyclotron resonance heating
(ICRH), has been recently reassessed for each of the four operational stages in the revised ITER
schedule [1]. Recently, it has been shown that a small amount of minority particles injected into a two-
ion plasma mixture can very efficiently absorb (nearly all) of the deposited RF power [2].
The application of these so-called three-ion species ICRH scenarios can be further extended to using
impurity ions as part of the plasma mix or as resonant ions, as well as using beam ions as resonant
species [3]. In this contribution, we give an overview of various three-ion ICRH scenarios that hold
promise for ITER operations and also highlight their possible applications beyond heating.
1) Heating full-field H plasmas, including impurities with (Z/A)imp < 1/2 such as 9Be, 40Ar and 22Ne,
with 4He as absorbing species (f ≈ 40 MHz) in the non-active phase. Since (Z/A)imp < (Z/A)4He < (Z/A)H,
the optimal 4He concentration for plasma heating depends strongly on the amount of intrinsic 9Be
impurities. In H-9Be plasmas, wave absorption by the 4He ions at very small concentrations is
maximized at n9Be/ne ≈ 2%. Additional injection of Ar or 22Ne impurities with a similar (Z/A)imp as for
9
Be has been proposed for further optimizing wave polarization and depositing ICRH power to 4He
minority ions [4].
2) Heating H-4He plasmas with 3He as absorbing species in the non-active phase. This scenario relies
on adding ~5–15% of 4He ions into H plasma, and a tiny amount of 3He ions (< 1%) to absorb RF
power. For full-field ITER operation, central 3He heating is achieved at f ≈ 54 MHz. The advantages
of this scheme in ITER include: i) more ICRH power is available at this frequency than at
f ≈ 40 MHz [5]; ii) reduction of the L-H power threshold by ~20% in H-4He mixtures (w.r.t. H plasma)
was reported in JET-ILW [6]. The lack of an efficient IC scenario at half-field ITER hydrogen
plasmas also led to the proposal to apply off-axis 3He heating in H-4He plasmas at 3T and 3.3T [4].
Note that off-axis 3He heating in equivalent H-D plasmas has been recently successfully shown in
AUG experiments [7].
3) Bulk ion heating in D-T plasmas with 9Be as absorbing species. The T-(9Be)-D heating scheme can
be exploited to enhance off-axis RF power absorption by 9Be impurities in full-field D-T plasmas in
ITER at f ≈ 40 MHz. Due to their higher mass, 9Be ions will effectively deposit absorbed RF power to
bulk D and T ions via Coulomb collisions, a feature particularly attractive for a fusion reactor. This
ICRH scenario is applicable for D:T=50:50 plasmas without the need to inject extra ions into the
plasma (an intrinsic concentration n9Be/ne < 1% would be sufficient). Central plasma heating with 9Be
impurities requires somewhat lower RF frequencies, f ≈ 38 MHz. Whether the ITER ICRH system can
operate at this frequency without too strong power degradation still needs to be assessed.
4) Using NBI ions as resonant species for ICRH heating of mixture plasmas. Efficient ICRH heating
of H-D plasmas with the fast injected deuterium NBI ions as resonant ‘third’ species was recently
demonstrated on JET [3]. Those ions in the beam distribution that have a Doppler-shifted cyclotron
resonance close to the ion-ion hybrid layer resonate with the excited fast wave and absorb RF power.
The ITER NBI heating system foresees injection of H and D neutrals at energies 0.87 MeV and
1 MeV, respectively. This allows to exploit NBI+ICRH synergies using the 4He-(HNBI)-H heating
scenario in 4He-H plasmas [8]. In a similar way, deuterium NBI absorption can be further enhanced
using the T-(DNBI)-D scenario to contribute to efficient heating of D-T plasmas in ITER.
[1] M. Schneider et al., Proc. 44th EPS Conf. on Plasma Physics, P5.153 (2017)
[2] Ye.O. Kazakov et al., Nature Physics 13, 973-978 (2017)
[3] J. Ongena et al., EPJ Web Conf. 157, 02006 (2017)
[4] M. Schneider et al., EPJ Web Conf. 157, 03046 (2017)
[5] P.U. Lamalle et al., AIP Conf. Proc. 1187, 265 (2009)
[6] J. Hillesheim et al., Proc. 26th IAEA Fusion Energy Conference, EX/5-2 (2016)
[7] A. Kappatou et al., this conference
[8] R. Bilato et al., this conference
