Speaker
Fabien Widmer
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1058.pdf
Modelling of NTM Stabilization by RF Heating and Current Drive in
Plasma with a Stiff Temperature Profile
F. Widmer1 , P. Maget1 , O. Février2 , X.Garbet1 , H.Lütjens3
1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
2 EPFL-SPC, CH-1015 Lausanne, Switzerland.
3 CPhT, Ecole polytechnique, CNRS, Université Paris-Saclay, Palaiseau, France.
Neoclassical Tearing Modes (NTM) are a class of MHD instability whose non-linear growth
is driven by the perturbation of the bootstrap current. Such instabilities must be controlled or
suppressed to prevent a degradation of the energy confinement for future devices. This can be
done applying RF-current (ECCD) or -heating (ECRH) at the rational surface where the instabi-
lity appears. We report on the modelling of NTM stabilization by the combined effects of ECCD
and ECRH depositions using the XTOR-2F code [1]. To consider the impact of the ECRH on
the NTM decay rate, it is necessary to take into account the Tokamaks turbulent transport pro-
perties related to a critical temperature gradient [2, 3]. Such properties are considered through
a heat diffusivity model depending on the stiffness σ only [4]. The stiffness and the ECRH
consequence on the NTM decay rate is highlighted by a scan in PRF /Peq with PRF the additi-
onal heat source centered at the O-point and Peq the power injected inside the island position.
Numerical simulations show that the island response to ECRH is on a short time scale. Also,
1/σ
the ECRH contribution to the NTM decay rate decreases as PRF /Peq . On the contrary, the
NTM reaction to ECCD acts during a longer time scale with a lasting effect on the island decay
rate. A good agreement between the ECRH and ECCD efficiencies deduced from the simulati-
ons and the theoretical predictions is found. Furthermore, the results show that the ECCD and
ECRH effects add up to contribute to the island decay. Finally, a generalized criteria for NTMs
stabilization by RF that integrates the heating effect in a plasma with stiff temperature profile is
derived.
References
[1] H. Lütjens and J.-F. Luciani, Journal of Computational Physics 229, 8130 (2010); O. Février, P. Maget, H.
Lütjens, et al., Plasma Physics and Controlled Fusion 58, 045015 (2016).
[2] W.A. Hornsby et al.,Physics of Plasmas 17, 092301 (2010); K. Ida et al., Phys. Rev. Lett. 109, 065001 (2012);
[3] A. M. Dimits et al., Physics of Plasmas 7, 969 (2000); X. Garbet et al., Plasma Physics and Controlled Fusion
46, B557 (2004). F. Imbeaux et al, Plasma Physics and Controlled Fusion 43, 1503 (2001).
[4] P. Maget et al., Physics of Plasmas (1994-present) accepted, (2018); P. Maget et al., (European Physical
Society, Prague (Czech Republic), 2018).
